Showing papers in "The Journal of General Physiology in 1960"

Regulation of cell volume by active cation transport in high and low potassium sheep red cells.

Abstract: A model cell which controls its cation composition and volume by the action of a K-Na exchange pump and leaks for both ions working in parallel is presented. Equations are formulated which describe the behavior of this model in terms of three membrane parameters. From these equations and the steady state concentrations of Na, K, and Cl, values for these parameters in high potassium (HK) and low potassium (LK) sheep red cells are calculated. Kinetic experiments designed to measure the membrane parameters directly in the two types of sheep red cells are also reported. The values of the parameters obtained in these experiments agreed well with those calculated from the steady state concentrations of ions and the theoretical equations. It is concluded that both HK and LK sheep red cells control their cation composition and volume in a manner consistent with the model cell. Both have a cation pump which exchanges one sodium ion from inside the cell with one potassium ion from outside the cell but the pump is working approximately four times faster in the HK cell. The characteristics of the cation leak in the two cell types are also very different since the HK cells are relatively more leaky to sodium as compared with potassium than is the case in the LK cells. Both cell types show appreciable sodium exchange diffusion but this process is more rapid in the LK than in the HK cells.

Thresholds and Plateaus in the Hodgkin-Huxley Nerve Equations

Abstract: ABS TR ncT Phase space methods and an analog computer are used to analyze the Hodgkin-Huxley non-linear differential equations for the squid giant axon membrane. V is the membrane potential, m the Na + activation, h the Na + inactivation, and n the K + activation. V and m change rapidly, relative to h and n. The (11, m) phase plane of a reduced system of equations, with h and n held constant at their resting values, has three singular points: a stable resting point, a threshold saddle point, and a stable excited point. When h and n are allowed to vary, recovery and refractoriness result from the movement with subsequent disappearance of the threshold and excited points. Multiplying the time constant of n by 100 or more, and that of h by one-third, reproduces the experimental plateau action potentials obtained with tetraethylammonium by Tasaki and Hagiwara, including the phenomena of abolition and of refractoriness of the plateau duration. The equations have, transiently, two stable states, as found in the real axon by these authors. Since the theoretical membrane conductance curves differ significantly from the experimental ones, further experimental analysis of ionic currents with tetraethylammonium is needed to decide whether the Hodgkin-Huxley model can be generalized to explain these experiments completely.

Na, Cl, and water transport by rat ileum in vitro.

Abstract: Interrelationships between metabolism, NaCl transport, and water transport have been studied in an in vitro preparation of rat ileum. When glucose is present in the mucosal solution, Na and Cl both appear to be actively transported from mucosa to serosa while water absorption is passive and dependent on net solute transport. Removal of glucose from the mucosal solution or treatment with dinitrophenol, monoiodoacetate, or anoxia inhibits active salt transport and as a result, water absorption is also inhibited. The dependence of water absorption on metabolism can be explained as a secondary effect due to its dependence on active salt transport. The relationship between salt and water transport has been discussed in terms of a model system.

Determination of equivalent pore radius for human red cells by osmotic pressure measurement.

Abstract: A new method has been developed to measure the equivalent pore radius in cellular membranes, and has been applied to human red cells. When red cells are suddenly introduced into a non-isosmolar concentration of non-lipid-soluble non-electrolyte molecules, water will enter or leave the cell. The rate of cell swelling or shrinking is determined and extrapolated to zero time to give the initial rate of volume change. By suitable adjustment of the concentration of the external solution the initial rate may be brought to zero. The transient equilibrium concentration, determined by interpolation from experimental data, gives a measure of Staverman's reflection coefficient, σ. The zero time method has enabled us to determine σ for nine permeant molecules. σ is directly related to the equivalent pore radius; the experimental data lead to a value of 4.2 A for the equivalent pore radius in man, in good agreement with the previous figure of 3.5 A given by Paganelli and Solomon. The zero time method offers a number of advantages over previous methods for determination of this parameter. It requires no measurement of the rate of water entrance into the cell, and is essentially independent of the kinetics of cell swelling. It may be applied to a variety of living cells so that many additional membranes may now be characterized in terms of their equivalent pore radius.

The influence of pH and ionic strength on the electrokinetic stability of the human erythrocyte membrane.

Abstract: The electrokinetic stability of washed normal human erythrocytes is discussed from the point of view of pH, ionic strength, and composition of the suspending medium. Many of the electrophoretic characteristics at low ionic strengths (sorbitol to maintain the tonicity), such as the isopotential points, are shown to arise principally from adsorption of hemolysate. The concept of electrokinetically stable, metastable, and unstable states for the red cell at various ionic strengths is introduced in preference to the general term "cell injury." In the stable state which exists around pH 7.4 for ionic strengths >0.007, no adsorption of hemolysate occurs, in the metastable state reversible adsorption of hemolysate occurs, and in the unstable state, in which ionic strengths and pH ranges are outside the metastable range, the membrane undergoes irreversible hemolysate adsorption or more general hydrolytic degradation. It is deduced from the equivalent binding of CNS, I, Cl, and F, the pH mobility relationships, and the conformation of the ionic strength data in the stable state to a Langmuir adsorption isotherm, that the membrane of the human erythrocyte behaves as a macropolyanion whose properties are modified by gegen ion association and in some instances by hemolysate adsorption. The experimental results are insufficient to establish conclusively the nature of the ionogenic groupings present in the membrane interphase.

Growth and Division of Single Cells of Higher Plants in Vitro

Abstract: The cultivation of single cells of Nicotiana tabacum L. var. "Samsun" and Phaseolus vulgaris L. var. "Early Golden Cluster" on a thin agar layer in Petri dishes is described. Under these conditions about 20 per cent of the cells divided repeatedly and established tissue clones which could be isolated and maintained as growing tissue cultures. It was possible also to follow the successive divisions of isolated cells and to observe their behavior during cytogenesis under the microscope.

The Response Properties of Single Ganglion Cells in the Goldfish Retina.

Abstract: A cross-section of any vertebrate retina shows a complex pattern in which many types of cells are interconnected. The functions of very few of these cell types are known in any detail. The rods and cones almost certainly absorb the light quanta and are responsible for the initiation of the train of events which culminates in the nerve impulse patterns of the ganglion cells whose axons form the optic nerve. This pat tern of nerve impulses is modified by the intensity, shape, and duration of the illumination falling on the retina. In a few types of vertebrate eyes it is also certain that the color of the stimulating light must modify the response patterns of different ganglion cells in a differential fashion. This is a requirement in any system of color vision, and it is fairly certain from behavioral experiments that these animals are able to distinguish colors. Many species of fish apparently can be trained to recognize colors. For this reason the fish retina is an appropriate place to find out how color information is encoded for transmission along the optic nerve. The response patterns of single ganglion cells of the vertebrate retina have been the subject of extensive study since Hartline's successful isolation of the ganglion cells of the frog retina. These response patterns were classified by Hartl ine (1938) into "on ," "off," and "on-off ' ' types according to the temporal relationship of the discharge to the illumination. These descriptive terms have been generally accepted by subsequent investigators and are in wide usage today. The response patterns of ganglion cells of a wide variety of other vertebrates have been examined by subsequent investigators. This work has indicated that the discharge patterns are basically similar. The "on-off ' ' type is most frequently seen and is looked on as playing the dominant role in the functional organization. The analysis of the response relationship

Color Vision Mechanisms in the Monkey

Abstract: The monkey, Macaca mulatta, was chosen as the experimental animal for the investigation of the physiological mechanisms of color vision for two reasons: there is excellent behavioral evidence that the rhesus monkey has color vision (this is not true for some of the animals which have been used in similar investigations); furthermore, its color vision system is undoubtedly very similar to, if not identical with, that of man. There is good evidence (Walls, 1942) that color vision systems have evolved several separate times, once in the insects, again in fish, reptiles, and birds, and still again within the primate order. If this is correct, it would be little more than a coincidence ff the way in which information about the wavelength of light is encoded in the visual system of monkey and man were the same as the manner in which it is accomplished in fish or birds. In any case, if one is interested in relating the ways in which various neural elements respond to different wavelengths of light under various conditions to the manner in which these lights are perceived, one cannot go wrong in studying an animal as similar as possible to man, for virtually all of the behavioral results from color discrimination have been obtained on the human observer. The macaque lateral geniculate nucleus (LGN), from which most of the recordings have been obtained, consists of six layers of cells separated by fiber layers. These cells receive connections from the axons of the ganglion cells of the retina and are thus the fourth-order neurons in the visual pathway. Anatomical studies (Glees and Le Gros Clark, 1941) have given little evidence for interconnections at this level; the types of responses recorded here may well be essentially the same as one would obtain from ganglion cells in the retina. However, the highly laminated structure of the LGN, in which the optic projection from each eye splits three ways, presents the possibility of some clues being present as to the nature of the organization of the visual system in the differential responses of cells in the various laminae. For this, as well as for certain technical reasons, the L G N rather than the retina was chosen as the recording site.

Osmotic Flow of Water across Permeable Cellulose Membranes

Abstract: Direct measurements have been made of the net volume flow through cellulose membranes, due to a difference in concentration of solute across the membrane. The aqueous solutions used included solutes ranging in size from deuterated water to bovine serum albumin. For the semipermeable membrane (impermeable to the solute) the volume flow produced by the osmotic gradient is equal to the flow produced by the hydrostatic pressure RT ΔC, as given by the van't Hoff relationship. In the case in which the membrane is permeable to the solute, the net volume flow is reduced, as predicted by the theory of Staverman, based on the thermodynamics of the steady state. A means of establishing the amount of this reduction is given, depending on the size of the solute molecule and the effective pore radius of the membrane. With the help of these results, a hypothetical biological membrane moving water by osmotic and hydrostatic pressure gradients is discussed.

Studies on the carrier function of phosphatidic acid in sodium transport. I. The turnover of phosphatidic acid and phosphoinositide in the avian salt gland on stimulation of secretion.

Abstract: Incubation of slices of the salt gland of the albatross with acetylcholine, which is the physiological secretogogue for this tissue, led to a 13-fold increase in the rate of incorporation of P32 into phosphatidic acid and a 3-fold increase in the incorporation of P32 and inositol-2-H3 into phosphoinositide. The incorporation of P32 into phosphatidyl choline and phosphatidyl ethanolamine was increased relatively slightly or not at all. Respiration was doubled. The "phospholipid effect" occurred in the microsome fraction, which is known to contain fragments of the endoplasmic reticulum. The enzymes, diglyceride kinase and phosphatidic acid phosphatase, which catalyze the stimulated turnover of phosphatidic acid in brain cortex, were also found in highest concentration in the microsome fraction. The phosphatides which respond to acetylcholine are bound to protein in the membrane. On the basis of these findings it appears that phosphatidic acid and possibly phosphoinositide participate in sodium transport. A scheme, termed the phosphatidic acid cycle, is presented as a working hypothesis, in which the turnover of phosphatidic acid in the membrane, catalyzed by diglyceride kinase and phosphatidic acid phosphatase, functions as a sodium pump.

Photoreactivation of transforming DNA by an enzyme from bakers' yeast.

Abstract: Ultraviolet-inactivated Hemophilus influenzae transforming DNA recovers its activity when mixed with cell-free extracts of bakers' yeast and exposed to visible light. The active agent in the extract is not used up in the reaction, and purification has not separated it into more than one non-dialyzable component. It differs from the agent in Escherichia coli extract, which produces very similar photoreactivation, but which can be resolved into non-dialyzable and dialyzable components, the latter being used up during illumination. The yeast agent can be salted out of solution and recovered quantitatively; it is inactivated by crystalline trypsin and chymotrypsin and by brief heating at 60 degrees C.-all facts suggesting that it is an enzyme for which ultraviolet lesions in the DNA serve as substrate. The kinetics of recovery are also consistent with such an assumption. This enzyme is unusual both because it is involved in a light-dependent reaction and because it has a non-destructive action on DNA outside an intact cell.

Ionic Current Measurements in the Squid Giant Axon Membrane

Abstract: The concepts, experiments, and interpretations of ionic current measurements after a step change of the squid axon membrane potential require the potential to be constant for the duration and the membrane area measured. An experimental approach to this ideal has been developed. Electrometer, operational, and control amplifiers produce the step potential between internal micropipette and external potential electrodes within 40 microseconds and a few millivolts. With an internal current electrode effective resistance of 2 ohm cm.(2), the membrane potential and current may be constant within a few millivolts and 10 per cent out to near the electrode ends. The maximum membrane current patterns of the best axons are several times larger but of the type described by Cole and analyzed by Hodgkin and Huxley when the change of potential is adequately controlled. The occasional obvious distortions are attributed to the marginal adequacy of potential control to be expected from the characteristics of the current electrodes and the axon. Improvements are expected only to increase stability and accuracy. No reason has been found either to question the qualitative characteristics of the early measurements or to so discredit the analyses made of them.

The surface of the washed human erythrocyte as a polyanion.

Abstract: The electrokinetic behaviour of normal erythrocytes is compared with that of trypsin-, N-bromosuccinimide-, and tosyl-treated erythrocytes. Reduction in the net negative charge with reduction in ionic strength of the suspending medium and also on treatment with N-bromosuccinimide and trypsin is discussed using a porous non-rigid polyanion as a model for the periphery of the cell membrane. It is deduced from the equivalent binding of chloride and thiocyanate ions and the absence of any effect on treatment of red cells with tosyl chloride, that normal, N-bromosuccinimide- and trypsin-treated cells are polyanionic in character. Reduction in erythrocyte charge on treatment with N-bromosuccinimide or trypsin is probably not due to the removal of phosphate groups from the interface, nor to physical adsorption of N-bromosuccinimide or trypsin. The charge reduction is probably produced by bond fission with possibly a net disappearance of carboxyl groups from the electrophoretic plane of shear either by loss from, or reorientation of, the membrane. The loss or reorientation of material associated with these carboxyl groups does not lead to any basic change in the character of the surface of the cell, nor to any obvious structural instability. The biconcave discoid form is maintained and there is no significant hemolysis of the erythrocytes even after contact with a solution of trypsin for 24 hours.

Na, Cl, and water transport by rat colon.

Abstract: Segments of the colon of anesthetized rats have been perfused in vivo with isotonic NaCl solutions and isotonic mixtures of NaCl and mannitol. Unidirectional and net fluxes of Na and Cl and the net fluxes of water and mannitol have been measured. Net water transport was found to depend directly on the rate of net Na transport. There was no water absorption from these isotonic solutions in the absence of net solute transport, indicating that water transport in the colon is entirely a passive process. At all NaCl concentrations studied, the lumen was found to be electrically negative to the surface of the colon by 5 to 15 mv. Na fluxes both into and out of the lumen were linear functions of NaCl concentration in the lumen. Net Na absorption from lumen to plasma has been observed to take place against an electrochemical potential gradient indicating that Na is actively transported. This active Na transport has been interpreted in terms of a carrier model system. Cl transport has been found to be due almost entirely to passive diffusion.

Neural photoreception in a lamellibranch mollusc.

Abstract: The pallial nerves of Spisula solidissima each contain a single afferent nerve fiber which responds directly to illumination of the nerve, and apparently mediates the "shadow" response of siphon retraction These units show constant-frequency spontaneous activity in the dark; illumination abruptly inhibits this discharge, and cessation of the light stimulus then evokes a prolonged burst of impulses at high frequency (the off-response) Impulses are initiated at a point near the visceral ganglion, and propagated unidirectionally toward it Stimulation with monochromatic light has revealed that more than one photoreceptor pigment is involved, since the discharge patterns evoked are wavelength-specific Inhibition is relatively prominent at short wavelengths, excitation at long wavelengths Following selective adaptation with blue light, "on" responses can be produced with red stimuli, demonstrating the unmasking of an excitatory event which takes place during illumination The two photoreceptor pigments may be segregated in two or more cells presynaptic to the recorded unit, or,—more likely—may both be contained in the same cell The spectral sensitivity function for inhibition shows a single maximum at 540 mµ, and is probably dependent upon a carotenoid pigment No photoreceptor function has been demonstrated for a hemoprotein, apparently identical with cytochrome h, which occurs in high concentration in Spisula nerve

Neuronal Activity in Cortical and Thalamic Networks : A study with multiple microelectrodes

Abstract: One of the major problems with which neurophysiological research has been confronted, in recent years, is the way in which the brain deals with the information that it receives over the sensory pathways. The study of this problem has been much enhanced by the development of techniques for the recording of the activity of single neurons. The use of such techniques has provided valuable information in two fields of investigation. One field, the electrophysiology of the brain cell: in this respect it has been found that electrical characteristics of cortical and thalamic neurons are very similar to those of neurons located elsewhere in the central nervous system (4, 5, 11, 16, 22), Another field, the study of the patterns of response of single brain cells to peripheral stimulation: in this respect it has been found that the latency of response, the number of spikes and the intervals between spikes generated by each individual neuron are related to the intensity, the frequency and the position of the peripheral stimulus (2, 3, 6, 7-10, 15, 17, 18, 23). Thus, cerebral neurons participate in the coding and the displaying of information upon the maps which, in the sensory receiving areas of the brain, represent the spatial, temporal, and other characteristics of events that occur in the outside world. Little is known, however, about the way in which the coded information displayed upon these maps is selected and organized in order to result in the processes which we call perception and integration. Whatever the mechanism of these processes may be, it is evident that, since it involves comparison, selection, and organization of sensory and memory data, it cannot be based on the activity of isolated neurons but it must be based on the interrelated activities of the large number of neurons which, with their connections, form the complex networks present in the brain stem and in the cortex. It is well known that some neurons in these networks are spontaneously

The Movement of Thallium Ions in Muscle

Abstract: Measurements have been made of the fluxes of thallous ions (Tl+) across the membrane of frog sartorius muscle fibers. These show that at an external concentration of 74 µM the influx is about 270 x 10-15 moles/cm.2 sec., while the efflux from a muscle with an internal concentration equal to the above is 5 x 10-15 moles/cm.2 sec. The efflux is increased of the order of 300-fold during a muscle twitch, and Tl+ reach a steady-state distribution between fiber water and Ringer solution that is very close to the corresponding ratio for K+. High concentrations of Tl+ depolarize the membrane about 58 mv. for a tenfold increase in external concentration. The results obtained are consistent with the view that the muscle fiber membrane cannot distinguish between the toxic heavy metal Tl+ and K+, provided that the concentrations of the former ion are kept low. High concentrations of Tl+, if allowed to act for an appreciable period of time, lead to irreversible damage to muscle.

The mechanochemistry of muscular contraction. I. The isometric twitch.

Abstract: The dependence of PC1 and ATP1 dephosphorylation on the number of isometric twitches in the iodoacetate-nitrogen-poisoned muscle has been examined. There is no net dephosphorylation of adenosinetriphosphate. PC dephosphorylation varies linearly with the number of twitches and produces equivalent amounts of C1 and P1i.1 Iodoacetate concentrations which block the enzyme, creatine phosphokinase, render the muscle non-contractile. A value of 0.286 µmole/gm. for the amount of PC split per twitch is obtained which gives a value of -9.62 kcal./mole for the "physiological" heat of hydrolysis of PC in agreement with expectations based on thermochemical data. In a single maximal isometric twitch it is estimated that 2 to 3 PC molecules are dephosphorylated per myosin molecule, or 1 per actin molecule. The results support the view that under the conditions of these experiments PC dephosphorylation is the net energy yielding reaction. The in vivo stoichiometry of the mechano-chemistry of contraction revealed by these studies on the one hand, and the known stoichiometry of actin polymerization and its coupling to the creatine phosphokinase system on the other are strikingly similar and strongly suggest that the reversible polymerization of actin is involved in a major way in the contraction-relaxation-recovery cycle of muscle.

Some Actions of Neurohypophyseal Hormones on a Living Membrane

Abstract: It has long been recognized that the antidiuretic hormone of the neuro hypophysis must have an action on the renal tubule which results in enhanced reabsorption of water. Ussing and Zerahn (1) have demonstrated in amphibian membranes that this hormone also stimulates active sodium transport. Whether it may in addition influence the reabsorption of other substances, however, has not been fully investigated. I should like to report some recent investigations which indicate: (a) that the hormone has a specific effect with respect to another major urinary constituent, urea, (b) that the cellular site of hormonal action can be localized, and (c) that a simple unitary hypothesis reasonably explains, at the present time, the observed actions of the hormone. Although our interest in this subject began with the mammal ian kidney, the difficulties inherent in studying that complex organ have led us to investigate an organ which is anatomically simpler, but which mimics the activities of the mammalian renal tubule in several important respects. Fig. 1 shows a histological section of the urinary bladder of the toad, Bufo marinus. The bladder is a bilobed structure which, in the intact animal, may occupy as much as one-half the abdominal cavity. Occasionally one sees a bundle of smooth muscle or a capillary in the bladder wall but most of the tissue appears, like that shown in higher magnification to the right, as a single layer of mucosal cells supported on a minimum of connective tissue.

The Binding of Mercury by the Yeast Cell in Relation to Changes in Permeability

Abstract: Yeast cells exposed to mercuric chloride suffer irreversible damage to the membrane, resulting in a loss of potassium and cellular anions to the medium. The maximal loss of K+, but not the time course of K+ loss is related to the mercury concentration, the relationship following a normal curve on a graph of log-concentration versus effect. It is concluded that the response is all or none for individual cells, and that with increasing concentrations of metal, the threshold is exceeded in an increasing proportion of the cells. Parallel studies of the binding of mercury by the cells indicate two distinct phases, only one of which is associated with the physiological response. The binding process is relatively slow but reaches an equilibrium state. Desorption is markedly dependent on temperature. No simple stoichiometric relationship exists between the binding of mercury and the physiological response (K+ loss).

Tracer exchange vs. net uptake of glucose through human red cell surface. New evidence for carrier-mediated diffusion.

Abstract: Previous kinetic studies of net sugar movements through the human erythrocyte surface (in response to concentration gradients) have led to postulation of a special "carrier" system for transfer of monosaccharides in these cells. But alternatively some sort of non-specific depression of cell permeability at high sugar concentrations has been suggested as a possible basis for the saturation kinetics and the competitive phenomena observed. New theoretical calculations show that these two interpretations predict entirely different orders of magnitude for the relative rate of tracer glucose exchange at such high sugar levels. Therefore, the speeds of gross chemical equilibration and of tracer glucose equilibration were compared by means of serial analyses on quickly separated cells and media, in thick red cell suspensions. Glucose was first added to glucose-free suspensions, and its entry into the cells followed; then C14-glucose was added after attainment of chemical equilibrium, and the tracer equilibration similarly followed. The speed of the tracer movement in relation to the speed of net uptake was on the order of 50 to 100 times greater than would be found in an uncomplicated diffusion process, regardless of what depressant effect might be occasioned by the high sugar levels. In contrast, the comparative rates observed are predicted by the previously proposed facilitated-diffusion mobile-carrier model for monosaccharide transfer, if the glucose-carrier complex is assigned a dissociation constant (at 20°C.) in the neighborhood of 1 mM.

The Nature and Significance of the Bohr Effect in Mammalian Hemoglobins.

Abstract: The oxygenation of hemoglobins is accompanied by the dissociation of protons. The number of protons discharged is inversely related to the size of the mammal from which the hemoglobin comes. The number of mercuric ions which are immediately bound by hemoglobins is approximately equal to the number of protons dissociated during oxygenation. Pretreatment of human hemoglobin by N-ethylmaleimide, which appears to bind only sulfhydryl groups prevents the binding of any mercuric ions under conditions when mercuric ions would otherwise be bound. These facts suggest that those mammals with higher metabolic rates will generally possess hemoglobins with a larger number of appropriately placed cysteine residues.

Evidences from Action Spectra for a Specific Participation of Chlorophyll b in Photosynthesis

Abstract: Rate of oxygen evolution in photosynthesis was measured as the current from a polarized platinum electrode covered by a thin layer of Chlorella. The arrangement gave a reproducibly measurable rate of photosynthesis proportional to light intensity at the low levels used and gave rapid response to changes in illumination. Two phenomena have been explored. The Emerson effect was observed as an enhancement of photosynthesis in long wavelength red light (700 mµ) when shorter wavelengths were added. Two light beams of wavelengths 653 and 700 mµ when presented together gave a photosynthetic rate about 25 per cent higher than the sum of the rates obtained separately. Large and reproducible transients in rate of oxygen evolution were observed accompanying change in illumination between two wavelengths adjusted in intensity to support equal steady rates of photosynthesis. The transients were found not to be specifically related to long wavelength red light. Both enhancement and the transients have identical action spectra which are interpreted as demonstrating a specific photochemical participation of chlorophyll b.

The action spectrum for shifting the phase of the rhythm of luminescence in Gonyaulax polyedra.

Abstract: The action spectrum for changing the phase of the rhythm of luminescence in the marine dinoflagellate Gonyaulax polyedra has been determined. Maxima in effectiveness were found at 475 and 650 mµ. The significance of these findings is discussed.

Red cell membrane structure and ion transport.

Abstract: The red cell in man is a biconcave disk, some 8.4/z in diameter, 2.4 # thick at its widest portion, and 1/z thick at its narrowest. I t is bounded by a membrane primarily composed of protein and lipid, the latter sufficient in amount to cover the red cell with a layer two molecules thick. The lipid layer is bounded on the outside, and possibly on the inside, by a layer of protein. The thickness of the membrane is not known accurately since the most reliable studies, those made with the electron microscope and by optical refraction, are necessarily made with dried material. The best estimates of membrane thickness lead to values of the order of 100/~. Within the human red cell, there is a high K concentration, 143 mu/ l i te r cell water, and a low Na concentration, 13.9 rn~/liter cell water. In the environment, the situation is reversed, since plasma contains 5.0 mM K and 154 mM Na/li ter plasma water (1-3). The present paper is concerned with the role of the cellular membrane in the creation and maintenance of these sharp differences in ionic composition across a barrier that is only a few molecules thick, a problem common to a wide variety of living cells. The conclusions are based on studies carried out in this laboratory in company with a number of associates, including R. Villegas, D. H. P. Streeten, V. Sidel, C. V. Paganelli, D. Goldstein, G. L. Gold, T. J. Gill, J. Evans, and T. C. Barton. The passage of alkali cations across the red cell membrane is very Slow, 3.1 rnM Na and 2.1 m_M K/l i ter cell hour (1, 2). In the case of the principal intracellular cation, K, this corresponds to a half-time for exchange of 31 hours. In contrast, C1, the principal anion, enters the red cell freely and exchanges with a half-time of 0,24 seconds (4). Since the electrophoretic mobilities of these two ions are closely similar, this difference is commonly interpreted in terms of a positive charge barrier in the channels which connect the interior of the cell with its environment. The charge density required to produce this 5 X 10Lfold difference in rates of entrance may be calculated approximately according to the equations given by Meyer and Sievers (5). This calculation is independent of the dimensions of the channels through which the ions are presumed to pass, and leads to a charge density within the channels of 106 M/liter. Since water is present at a concentration somewhat less than 55 M/liter, the charge density of 106 M/liter is clearly impossible of achievement. However, as Sollner has pointed out (6), in the limit when the channels are Small enough, a single positive charge will suffice to block the

Biochemical Studies on Amphibian Metamorphosis : I. The effect of thyroxine on protein synthesis in the tadpole

Abstract: Thyroxine has been shown to accelerate the synthesis of carbamyl phosphate synthetase in the liver of Rana catesbeiana. Stimulation of carbamyl phosphate synthetase synthesis by thyroxine appears to be relatively specific because of the following observations: (1) succinoxidase activity decreased during the time that carbamyl phosphate synthetase increased; (2) liver catalase responded more slowly than carbamyl phosphate synthetase to thyroxine; (3) the ratio of biochemical changes/morphological changes was greatly altered during thyroxine-induced metamorphosis. The relationships between the concentration of thyroxine and (1) temperature; (2) duration of exposure of the tadpole to thyroxine; and (3) the activity of carbamyl phosphate synthetase during the induced synthesis of carbamyl phosphate synthetase by thyroxine are discussed. Chloramphenicol and thiouracil partly counteracted the effect of thyroxine on the synthesis of carbamyl phosphate synthetase.

Characterization of the membranes in the giant nerve fiber of the squid.

Abstract: There are several methods by which the structure of a cell may be studied. The electron microscope makes it possible to visualize details of the ultrastructure, and to resolve these details with a resolution of 10 ~. Membranes may also be characterized in terms of the molecules which diffuse across them, leading to a resolution which may be an order of magnitude greater. It is the object of the present study to examine the giant nerve fiber of the squid by both of these methods to see if the combination will clarify the picture of the nerve membrane. The questions to be explored are: (1) are there any channels in the Schwann cell which have not been previously detected? (2) where is the barrier to the diffusion of water into the axoplasm? (3) are the barriers to diffusion and filtration the same?and (4) can the axolemma be characterized in terms of an equivalent pore radius? The final point of inquiry is whether the structure thus elucidated bears any relation to the ion transport mechanism which has already been so thoroughly explored (1).

The Nature of the Retinal Action Potential, and the Spectral Sensitivities of Ultraviolet and Green Receptor Systems of the Compound Eye of the Worker Honeybee

Abstract: 1. The retinal action potential consists principally of a sustained negative wave which persists for as long as the stimulus. Transitory negative on-effects and off-effects may also be present, particularly at long wave lengths (green, yellow, and red) and in the light-adapted eye. 2. Only the maintained component of the potential can be elicited under CO(2) anesthesia. The transient components are reversibly eliminated from the response at about the same time as the background noise of nerve and muscle spikes. It is suggested that the sustained component arises from the receptor cells, and the other components from second and higher order neurons. 3. The compound eye does not contain a homogeneous population of receptors. A green receptor system (maximum sensitivity at about 535 mmicro) determines the response of the dark-adapted eye throughout most of the spectrum; during adaptation to yellow light, however, an ultraviolet receptor system is revealed, with maximum sensitivity at about 345 mmicro. The anatomical bases of these receptor systems are unknown; however, they include both retinula cells and neurons in the optic ganglion. 4. There is no change in spectral sensitivity (Purkinje shift) in the first three logarithmic units above the threshold of the retinal action potential. 5. The relatively great effectiveness of near ultraviolet light in stimulating the positive phototaxis of the bee does not depend on excitation of the ultraviolet receptor of the ocellus.

On the R membrane in the frog's eye: its localization, and relation to the retinal action potential.

Abstract: It was reported by Brindley (1, 3, 5) that there is a layer of high electrical resistance and capacitance termed the R membrane in the retina and that the E R G develops across this membrane. He considers that the R membrane is the external limiting membrane. O n the other hand, Brown and Wiesel (6) who worked more recently on the unopened cat's eye with microelectrodes concluded that the P, membrane is not the external limiting membrane bu t Bruch's membrane lying just back of the pigment epithelium. I t will be reported in this paper that (a) our results obtained from the excised opened eye of the frog support the conclusion of Brown and Wiesel, (b) the R membrane is an important physical factor that determines the configuration of the intraretinally recorded action potential, and (c) some of the conflicting evidence concerning the origin of the E R G obtained with microelectrodes can be resolved in terms of this factor.