Showing papers in "Pflügers Archiv: European Journal of Physiology in 1972"

Differentiation of the transmembrane Na and Ca channels in mammalian cardiac fibres by the use of specific inhibitors

Abstract: According to earlier studies on mammalian papillary muscles, verapamil and compound D 600 (a methoxy-derivative of verapamil) can abolish the Ca dependent contractile responses completely whilst the Na dependent action potentials persist. In an attempt to clarify the mechanism of action separate measurements of the transmembrane Na and Ca currents have been performed on ventricular trabeculae of cats using a special voltage clamp technique. The following results were obtained: As a functional significance of this dual membrane transport system it is possible to change the contractile force by inotropic substances which act on the Ca conductivity without a corresponding influence on excitation.

Inward membrane currents in mammalian myocardium

Abstract: 1. Voltage clamp experiments (intracellular electrode for voltage control, current applied through a sucrose gap) were carried out in cat myocardium with an improved clamp circuit. The improvements were: a) reduction of series resistance by clamping the extracellular bath to earth potential and b) monitoring the longitudinal core resistancer ig of the fibres and the shunt resistancer eg in the gap. 2. Ratios ofr ig /r eg <1 (usually due to increase ofr ig because of decoupling of the cells in the gap) cause artifactual current wave forms of the configuration of a more or less suppressed “action potential”. The artifactual component of the recorded current flows through the shunt resistance. 3. In most preparations, shorter than 1 mm, cable properties do not permit space clamp (tested with a second intracellular electrode). Both the rapid sodium current and a slow inward current differing in threshold, amplitude and time course “escape” and produce voltage gradients making measurement of membrane current incorrect. In these preparations the configuration of the current trace depends on the position of the intracellular electrode in the voltage control circuit. 4. In preparations of suitable geometry, smallr ig /r eg ratio and small series resistance space clamp is achieved. Under this condition the two inward currents are clearly separated from each other. 5. The threshold of the slow inward current is at −35 mV. The maximum amplitude of the slow inward current amounts to 1–5 μA (preparation length and diameter about 0.5 mm). A plot of h∞ vs. membrane potential shows inactivation of the slow inward current between −50 mV and −20 mV. 6. Following a depolarization step the slow inward current is turned on with a delay of a few milliseconds. Its activation time amounts to about 20 ms at threshold and 6–8 ms at zero potential. Its inactivation time constant amounts to 60–70 ms between −25 mV and +10 mV, being much longer outside this range.

The ionic nature of slow inward current and its relation to contraction.

Abstract: In voltage clamp experiments on cat myocardium the slow inward current as affected by the extracellular calcium and sodium concentration was studied In some of the experiments, contraction was simultaneously recorded and related to membrane potential and slow inward current The following results were obtained: 1 The amplitude of the slow inward current decreases on lowering the extracellular calcium concentration In zero calcium slow inward current is not observed 2 The slow inward current is not affected by lowering the sodium concentration in the bathing solution to 10% of the normal concentration 3 The membrane conductance is increased during the slow inward current by a factor of about 2 and not fully inactivated during maintained depolarization 4 The threshold potential for both slow inward current and contraction is at −35 mV 5 At potentials more positive than +80 mV (at 36 mM extracellular calcium) and more positive than +40 mV (at 09 mM calcium) the amplitude of the contraction declines Also slow inward current reverses polarity at these potentials and calcium concentrations 6 The amplitude of the steady state contraction rises with the amplitude of clamp depolarization in an S-shaped manner from threshold to the maximum of contraction at zero millivolt Plotted in normalized fashion (maximum amplitude of contraction = 1), the curve relating amplitude of contraction to clamp potential is shifted by 66 mV in negative direction when the extracellular calcium concentration is reduced by a factor of 4 7 Reduction of extracellular sodium results in large increase of amplitude of contraction The plot of normalized amplitude of contraction vs clamp potential is shifted towards negative membrane potentials and both, the reversal potential of slow inward current and the maximum amplitude of contraction, occur between +10 mV and +30 mV

The action of lanthanum and D600 on the calcium exchange in the smooth muscle cells of the guinea-pig Taenia coli.

Abstract: The calcium distribution in smooth muscle cells of the taenia coli has been studied with a method based on the action of lanthanum ions. La3+-ions make it possible to separate the extracellular calcium from the cellular calcium by their high affinity for extracellular calcium binding sites and by their blocking action on the transmembrane calcium movements. Using this method the cellular calcium content and its exchangeable fraction have been determined. In spontaneously active tissues the exchange of the cellular calcium reaches a maximal value of 108 μM/kg wet wt or 1/6 of the total cellular calcium, while in quiescent tissues (treated with D600) this maximal value is 80 μM/kg wet wt.

Selective suppression of some components of spontaneous activity in various types of smooth muscle by iproveratril (Verapamil).

Abstract: Intra- and extracellular measurements of electrical activity were recorded simultaneously with tension development from isolated preparations of taenia coli, portal vein, stomach and ureter of the guinea-pig. Iproveratril (verapamil) inhibits electrical and mechanical activity in parallel in spontaneously active preparations of taenia coli and portal vein. Spike discharges and second-rhythm (SR) oscillations are both suppressed in the electrical activity. In portal vein, the relatively weak basic organ specific rhythm (BOR) of this tissues is also suppressed. The minute-rhythm (MR) appears less sensitive or resistant to iproveratril. In ureter and antrum preparations of the stomach there is an additional iproveratril resistant component: the basic electrical process of stomach and ureter peristalsis which, in the classification of smooth muscle rhythms, belongs to the type BOR. The superimposed spike potentials of the antrum and the spike-like oscillations of the ureter action potential are inhibited similarly as are the spike potentials in taenia coli and portal vein. The similarity between the iproveratril effects and the effect of Ca-deprivation indicates a Ca-antagonistic action of iproveratril. Conclusions concerning the hypothesis of “Ca-spikes” in smooth muscle are discussed.

Quantitative continuous measurement of partial oxygen pressure on the skin of adults and new-born babies.

Abstract: It is possible to perform continuous quantitativePO2 measurements on vasodilated skin by means of surface Pt electrodes according to Clark when the electrode is fixed to the skin with a synthetic plastic material and in situ calibration is performed. A new in situ calibration of thePO2 electrode is described. At first the skinPO2 increases with O2 inspiration. After perfusion stop the skinPO2 shows a linear decrease because of the skin respiration, down to aPO2 at which hemoglobin liberates chemically bound O2. As thisPO2 value of hemoglobin is known it is possible to use it for calibrating the electrode. ThePO2 of normal skin is about 0–7 Torr. After vasodilation obtained by rubbing with a nicotinic acid derivate (Finalgon®, Anasco, Wiesbaden),PO2 increases to a mean value of 38.1 (±8.1) Torr (n=77). Under these conditions, skinPO2 reaches arterial values never in adults and rarely in new-born babies.

Membrane potential and slow inward current dependence of frog cardiac mechanical activity.

Abstract: Both contractile response and ionic currents are recorded during voltage clamp experiments on frog atrial trabecles. In Ringer solution, tension elicited by depolarizing steps of different duration and amplitude may be considered as composed of two elements. One depends on the slow inward current; the estimated variation in [Ca++]i can account for the tension elicited. At its level, the competition between Ca and Na ions is manifest. The other component, depending on the membrane potential, exists even in absence of external Ca ions. Such a component of mechanical response suggests an intracellular source of activator-calcium and these ions can be displaced by membrane potential. Moreover, both this component and the absence of threshold in the tension development agree with the fact that the membrane potential controls the diastolic tension. These two components share in the contraction elicited by action potential.

Microrheology and light transmission of blood. I. The photometric effects of red cell aggregation and red cell orientation.

Abstract: SummaryThe well known flow dependence of the optical density of whole blood was studied by measuring light transmission of blood in viscometric flow. A cone-plate chamber (3° cone angle) was transilluminated (λ=500–800 nm) while under shear (0–460 sec−1). The transmitted light was monitored with a selenium barrier layer photocell and was continuously recorded. In an identical chamber, the microrheological behaviour of the cells in flow was monitored by microphotography and then correlated to photometric events.Light transmission of human blood showed a biphasic behaviour when plotted as a function of shear rate: between 0 and about 60 sec−1, the light transmission decreases with shear, corresponding to aggregate dispersion. Above 60 sec−1, an increase of light transmission with shear occurs, corresponding to red cell deformation, alignment, and orientation. Bovine blood, which does not form aggregates, shows minimum light transmission at rest. Light transmission then rises progressively with shear from the very onset of slow flow. Equine blood (equus zebra) which has very strong aggregation shows a progressive decrease of light transmission with shear due to aggregate persistence up to 460 sec−1. Amphibia blood (rana esculanta) shows very pronounced increase in light transmission at low shear rates, but no progression with shear. The nucleated amphibia erythrocytes are oriented but not deformed in flow. Rigidified cells which neither aggregate nor become oriented in flow show no flow dependent changes in light transmission. It became evident that in all blood samples minimum light transmission was recorded when the cells were dispersed and randomly oriented; both aggregation and orientation produced increased light transmission. These results explain earlier controversies in the literature, they shed doubt on the existence of a “tubular pinch effect” in whole blood rheology.

Thermoregulatory responses of the pigeon to changes of the brain and the spinal cord temperatures

Abstract: 1. The thermoregulatory responses of pigeons were tested by selective and combined cooling and heating of thermodes implanted chronically into the brain stem and vertebral canal. 2. Under thermoneutral conditions lowering the brain temperature to 36°C did not elicit shivering. Similar stimulations of the spinal cord evoked shivering in each case. Simultaneous temperature changes in same direction (cooling the brain and spinal cord) or in opposite direction (heating the brain and cooling the spinal cord) could not influence the intensity of shivering due to cooling the spinal cord alone. Thermal stimulation of the brain stem did not affect shivering due to environmental cold, whereas this response was intensified by cooling and diminished by heating the spinal cord. 3. Selective heating of the brain to 44°C rarely induced panting, whereas heating the spinal cord to 42–43°C resulted generally in polypnea under thermoneutral conditions. Opposite changes at both sites (heating the spinal cord and cooling the brain) inhibited panting due to heating the spinal cord in 3 of 12 cases. Under conditions of environmental heat, persisting thermal panting was often inhibited by cooling the spinal cord, but hardly affected by cooling the brain stem. 4. Cooling the brain as well as the spinal cord raised the feathers (piloerection) and lowered the skin temperature of the naked feet (vasoconstriction). Both reactions were affected to about the same extent by stimuli in each of the two parts of CNS. 5. The results suggest that the temperature signals generated in the brain stem of the pigeon especially effect piloerection and vasomotor reactions. These responses enable the animals to maintain a constant deep body temperature under mild thermal load. Changes of the spinal cord temperature chiefly drive shivering and panting which avoid hypo- and hyperthermia of birds under stronger thermal stress.

Microrheology and light transmission of blood. II. The photometric quantification of red cell aggregate formation and dispersion in flow.

Abstract: SummaryThe non-Newtonian viscosity of blood is caused by aggregation of red cells into three dimensional structures at low shear rates, causing high viscosity and the yield shear stress, progressive dispersion of these aggregates and eventually fluid drop-like transition of red cells at high rates of shear. Both the aggregated and the fluid drop-like state of the red cell can be characterized by the effect on apparent viscosity and by direct microscopic observation of the flowing blood. However, the transition between these two rheological states of the red cell could previously not be quantified. By monitoring their optical effects (as measured by light transmission under flow) rather than their mechanical effects (as measured by viscometry) the shear rates and thus the shear stresses necessary to keep red cell aggregates dispersed were determined. In addition, the degree of red cell aggregation at slow flow and the rate of aggregate reformation were quantified. After plasma dilution, all effects of red cell aggregation were less pronounced; after the addition of high molecular weight dextran, all effects of red cell aggregation were more pronounced. Lowering temperature down to 2°C intensified red cell aggregation, the shear stresses necessary to keep aggregates dispersed increased 8.5 times. This method allows for the first time to quantify under flow the kinetics of intensified red cell aggregation, the most common hemorhelogical abnormality.

The effect of repetitive stimulation at low frequencies upon the electrical and mechanical activity of single muscle fibres.

Abstract: 1. The effect of repetitive stimulation at low frequencies (0.2–5/sec) upon isometric twitch tension was analysed in isolated muscle fibres of the frog. 2. The number of twitches until tension decreased to 10–20% of the original value (fatigue effect) was 5000–10000 in unpoisoned fibres at 20° C, 400–800 in CN-poisoned fibres at 10° C, 1800–2500 in CN-poisoned fibres at 20° C and 100–200 in CN and IAA-poisoned fibres at 1° C. 3. In fatigued fibres the overshoot of the action potential was often only a few millivolts lower than in normal fibres, the spike duration was longer, and the after-potential was increased. 4. In completely exhausted fibres, which developed no tension when they were activated, the effective memrane resistance was extremely low, the resting potential was high, and early and late after-potentials were absent. Since an exchange of external Cl by SO4 caused no depolarization, it is suggested that the decrease in resistance is due to an increase in potassium conductance. 5. A reduction of the external sodium concentration from 115 to 46 mM abolished the overshoot of the action potential, while twitch tension remained unaltered. 6. In fatigued fibres normal twitch height could be restored by the addition of caffeine, and maximal contracture tension could be obtained after a complete depolarization in a potassium sulphate solution which contained caffeine. 7. From the results quoted under 3, 5, and 6 it is concluded that neither an alteration in the action potential nor an exhaustion of energy reserves or a failure in the contractile mechanism can be regarded as the cause of fatigue. 8. In fatigued fibres the S-shaped curve which relates peak tension to membrane potential (threshold curve) was shifted by about 20 mV to more positive potentials. In addition maximal contractile strength was frequently no longer attained, even after complete depolarization. 9. The rate by which the contractility of depolarized fibres can be reactivated after a sudden repolarization, and probably also the steady relation between the state of the contractile system and membrane potential, were equal in normal and fatigued fibres. 10. Fibres recovered from fatigue within one to three hours. 11. From the results quoted under 8 and 9 it is tentatively suggested that a decline of the concentration of an “activator of contraction”—localized in some part of the tubular system—is the cause of the observed deficiency in excitation—contraction coupling.

Phosphate, calcium and magnesium transfers in proximal tubules and loops of Henle, as measured by single nephron microperfusion experiments in the rat.

Abstract: Oil blocked superficial proximal tubules were microperfused in situ (30 nl/min) with physiological solutions labelled with45Ca,32P i and3H-inulin containing either 2 mM (normal P i ) or 0.6 mM (low P i ) as phosphate concentrations. Fluid was successively collected from the first distal, the last proximal and one or two other proximal convolutions of each perfused nephron. 3H,45Ca and32P radioactivities were measured by liquid scintillation with appropriate energy discrimination. P i , Ca and Mg concentrations were determined by electron probe analysis. Net and unidirectional fluxes were calculated for each tubule from the data provided by paired samples. The results indicate that: Mean values for unidirectional and net fluxes of P i and calcium in the proximal are given in the tables as pmoles per min per mm of tubule, as well as mean values for the net absorption flux of Ca, Mg andP i within the loops (pmoles per min per loop).

Water and electrolyte secretion by the exorbital lacrimal gland of the rat studied by micropuncture and catheterization techniques.

Abstract: There have been very few studies performed on electrolyte excretion by the isotonic-secreting lacrimal gland and none at all on the composition of its primary secretion. We have attempted both of these on the readily accessible rat exorbital lacrimal gland. From micropuncture studies we find the following electrolyte concentrations in the primary secretion which are unaltered by stimulation of gland secretion with carbachol:[Na]=139 mM±4(S.E.M.); [K]=9.0±1.2 mM; [Cl]=105±3 mM. By using fine-bore (80 μm) polyethylene tubing we were able to collect samples of final lacrimal secretion from the gland main duct. Na concentrations were usually similar to those in primary fluid but K concentrations were very high (46±3 mM) and rose at low secretory rates to about 140 mM. Cl concentrations (123±1 mM) were significantly greater than those in the primary secretion and in the interstitial fluid but were independent of secretory rate. HCO3 concentrations were also independent of secretory rate and averaged 19.6±2 mM. The results show that the lacrimal excurrent duct system plays a role in determining the composition of the final secretion. Contrary to previous studies in human and rabbit lacrimal glands, the present studies on the rat lacrimal reveal flow dependency of the concentrations of some electrolytes which may have been obscured in earlier studies where the slowly flowing lacrimal secretion was allowed to come into contact with the conjunctival epithelium before collection.

Differential action of TEA+ on two K+-current components of a molluscan neurone

Abstract: Snail neuronal membranes have two distinct outward current components. Both components are carried by K+-ions. They are, however, differentially influenced by Tetraethylammonium. At low concentrations in the external bath (5 mM), TEA+ blocks the delayed outward current only. The fast outward current is affected if higher TEA+ concentrations are used. Intracellular TEA+, applied iontophoretically, blocks both current components in a similar manner.

Cardiac hypertrophy, capillary and muscle fiber density, muscle fiber diameter, capillary radius and diffusion distance in the myocardium of growing rats adapted to a simulated altitude of 3500 m.

Abstract: In growing rats adapted to a simulated altitude of 3500 m for about 4 weeks and in their controls the evolution of cardiac ventricular weight was followed. The increase of total ventricular weight found in the adapted animals can be attributed exclusively to the increase of right ventricular weight. In other adapted and control animals cardiac capillary densities, muscle fiber diameter and external capillary radius were estimated and fiber—capillary ratio and diffusion distance were calculated. There was an increase of capillary density together with a decrease of muscle fiber density, fiber-capillary ratio and diffusion distance in the right but not in the left ventricle of the adapted rats. The muscle fiber diameters, however, were larger in both heart ventricles of the rats exposed to a simulated high altitude, especially in the right ventricle. This indicates that true hypertrophy of the muscle fibers is mainly responsible for the increase of right ventricular weight. In the left ventricle, however, a hypertrophy of the muscle fibers together with a decrease of stroma components is demonstrated. The physiological importance of the shorter diffusion distance in the right ventricle of the high altitude adapted rats is discussed and it is suggested that the shorter diffusion distance may help to keep the tissue O2 partial pressure above the critical value, mainly also in extreme situations with high myocardial O2 consumption.

Comparative force-frequency relationships in human and other mammalian ventricular myocardium.

Abstract: Contractile responses to increased stimulation frequency were analyzed in isolated papillary and ventricular muscle bundles from human, guinea pig and rat hearts. Contractile tension and velocity of tension development and release were recorded while changes in frequency were made. The following were calculated for each frequency; duration of the phases of accelerating (I) and decelerating (II) contraction, and accelerating (III) and decelerating (IV) relaxation; tension at end of phases I, II and III; and instantaneous velocities at the midpoint of phase I, and at the end of phases I and III. Increasing frequency was accompanied by decreased contractile tension and velocities to a limit in rat and markedly hypertrophied adult human myocardium; but by increased contractile tension and velocities to a limit in guinea pig, late fetal human, and minimally hypertrophied adult human myocardium. The observations support the hypothesis that peak contractile tension development depends on phase I velocity and phase II duration.

Modifications of single and double-barrel potassium specific microelectrodes for physiological experiments

Abstract: 1. The shape parameters of glass microcapillaries for making ion specific microelectrodes were studied. It was found, that the greater the angle set by the walls, the more advantageous is the shape for filling the microelectrode. The time response of the precisely prepared microelectrode does not exceed severall msec. 2. The preparation of the double-barrel ion specific microelectrodes is described. One barrel was filled with organic ion exchanger and the other with NaCl solution (reference channel). These electrodes are convenient for measurement of ion movements in the excitable tissues (brain, spinal cord etc) where it is necessary to avoid the electrical activity of the cells. 3. A side-pore type of ion specific microelectrode was developed for measurement of extracellular K+ concentration during muscle contraction. This type of electrode does not cut the muscle fibres during contractions and the side orifice of the channel prevents the undesirable movement of the ion exchanger during insertion into the muscle.

Autoregulation of contractility in the myocardial cell. Displacement as a controlling parameter.

Abstract: An investigation was carried out on isolated cat's papillary muscle in order to study displacement effects upon the intensity and the time course of the contractile activity. Displacements occurring before or very early during a contractile cycle produce effects which can be entirely explained on the basis of the cardiac active length-tension relation. Displacements occurring later exhibit additional effects in so far as either stretches or releases induce a drop of contractile activation such that the course of the subsequent tension development is markedly below that of the same displacement applied earlier. In order to separate these effects from those based on the active length-tension correlation experiments were performed in which very short release-stretch or stretch-release operations were applied so that the muscle length was virtually the same at the beginning and at the end of the operation. The results obtained under these conditions can be summarized as follows. The extend to which contractile tension drops after a stretch-release or a release-stretch cycle has been applied depends upon (1) the stimulus intervention interval (2) the length change performed (3) the velocity of displacement during the intervention. It is not dependent on the initial muscle length. Increasing the extracellular Ca-concentration considerably reduces the displacement effects. The results are tentatively explained by assuming an internal feedback loop between a variable of the contractile machinary and the preceding mechanism of activation.

Renal handling of 3'-5'-cyclic AMP in the rat. The possible role of luminal 3'-5'-cyclic AMP in the tubular reabsorption of phosphate.

Abstract: 3′-5′-cyclic AMP, phosphate and calcium renal excretions were studied in rats in different physiological states and submitted to various hormonal treatments: Lysine-vasopressin, parathormone (PTH) and glucagon injections. Simultaneous measurement of the specific radioactivities of 3′-5′-cyclic AMP in plasma and urine during steady state infusion of tracer, amounts of3H 3′-5′-cyclic AMP made it possible to determine the contributions of renal synthesis and secretion of 3′-5′-cyclic AMP to overall urinary excretion of the cyclic nucleotide. The infused3H 3′-5′-cyclic AMP was rapidly cleared from the plasma (mean total clearance 3.7 ml/min/100 g). Renal clearance contributed about 25% to the total clearance; its mean value represented about 75% of the glomerular filtration rate and was not modified by large plasmatic loads of 3′-5′-cyclic AMP.

Pelvic urine composition as a determinant of inner medullary solute concentration and urine osmolarity.

Abstract: To clarify the question whether solute and water fluxes between pelvic urine and the renal papilla contribute to the medullary accumulation of osmotically active substances and thus to final urine concentration, we measured the osmolarity of urine samples from the papillary tip of rat kidneys during superfusion of the exposed papillae with solutions of widely varying osmotic concentrations. When the osmolarity of the superfusion fluid consisted half of urea and half of sodium chloride, urine osmolarity was observed to change parallel to the bath solution over a certain concentration range (800–2000 mosm/l). The changes of urine concentration occurred within 90 min after the start of the papillary superfusion. Similar results were obtained when the sodium chloride concentration was kept constant at 300 mosm/l and the urea concentration varied to yield bath concentrations up to 3000 mosm/l. A rise of urine concentration by papillary superfusion above 2000 mosm/l was achieved when exogenous arginine-vasopressin was infused intravenously suggesting that the failure of urine concentration to equilibrate with the bath concentration was due to a limited water permeability of the collecting ducts. These results suggest that solute and water fluxes between pelvic urine and the renal papilla are a necessary prerequisite to achieve maximal osmotic urine concentrations. In addition, such fluxes may explain the variability of medullary tissue concentrations under various diuretic states.

Regional differentiation of sympathetic activity during peripheral heating and cooling in anesthetized rabbits.

Abstract: Thermal stimuli applied to roughly one half of the body skin in anesthetized and paralyzed rabbits evoked antagonistic changes of regional sympathetic activity. Peripheral cooling resulted in an increase of cutaneous sympathetic activity, while visceral sympathetic activity decreased. Peripheral heating induced a decrease of cutaneous sympathetic activity and simultaneously an increase of visceral sympathetic activity. The same antagonism has been found during central nervous thermal stimulation at different levels. This identity of vasomotor patterns reveals that qualitative differentiation of regional outflow represents a typical thermoregulatory response of the sympathetic system.

Experimental myotonia in mammalian skeletal muscle: changes in contractile properties.

Abstract: When myotonia is induced in rat diaphragms either by addition of 2,4-dichlorphenoxyacetate to the solution in which the excised muscle is bathed or by feeding animals on 20,25-diazocholesterol, the most significant change in membrane properties of the myotonic muscle fibres is an increase of the specific membrane resistance by a factor of 2 to 2.5. Membrane resting potential and capacitance are not altered. Like in healthy muscle, in 20,25-induced myotonic muscle the fibre membrane does not show rectifier properties ± 12 mV around the resting potential. The threshold for eliciting an action potential is unchanged but it is easier to start a burst of action potentials with a suprathreshold stimulus.

Mechanical activity and ionic currents in frog atrial trabeculae

Abstract: 1. The relationship between ionic currents and contraction has been investigated in sinoauricular trabeculae of the frog. A double “sucrose gap” technique combined with an optical system permits the measurement of the contraction of the small area where current was recorded. Changes in light intensity were similar to isotonic mechanical response reported for cardiac muscle. 2. In Ringer's, above the mechanical threshold, depolarizations longer than the action potential induced contractile responses associated with inward, outward and tail currents. Variation of the depolarizing step duration revealed the presence of two components in the contraction. 3. A fast contraction with a threshold between + 35 and + 45 mV was evoked preferentially by short depolarizations (below 100 msec). This contraction was not markedly influenced by the fast inward current (as shown by the effect of TTX), on the other hand the slow inward current and contraction are both abolished by Mnsolutions. When [Na]0 is reduced to 10% of the normal, the slow inward current and the contraction are altered by variation of the depolarization amplitude or of the [Ca]0 in a similar way, results which favour a link between the slow inward current and the fast contraction. 4. A slow contraction, with a threshold in the region of + 70 mV, was observed in solutions containing manganese with depolarizations above 100 msec duration. It is suggested that this contraction may be induced by release of calcium from intracellular stores.

Mesure de la vitesse de renouvellement du lactate chez le rat par perfusion de 14-C-U (l) lactate

Abstract: 1. Lactate turnover was measured in 24 anesthetized rats using14C-U-(l) Lactate with the priming dose-infusion technique. 2. 14C Lactate in blood was determined with a specific radio-enzymatic micromethod. 3. Lactate turnover increases with blood lactate concentration in the range 0.5 to 3 mM. In a steady state system this relationship means that a new equilibrium may be achieved at a higher pool level, between lactate production and utilization. 4. Comparing available data in four mammalian species lactate turnover at normal lactate levels was found to be approximately constant when computed on a body surface unit basis.

Intracellular potassium in cells of the distal tubule.

Abstract: Using a new double-barreled K+-selective liquid ion-exchange micro-electrode effective intracellular [K+] and the peritubular PD were measured simultaneously in single cells of the distal tubule of the rat kidney. The transepithelial PD was measured in the same kidney. A mean [K+] of 46.5±1.6 mM was obtained in the distal tubule cells of normal rats. The effective intracellular [K+] increased significantly to 60.5±2.1 mM with chronic K+ loading and to 51.5±0.9 mM with metabolic alkalosis, and decreased significantly to 36.5±2.6 mM with chronic K+ depletion and to 38.7±1.4 mM with metabolic acidosis. The luminal membrane PD was depolarized in the kaliuretic states of K+ loading and alkalosis and hyperpolarized in the kaliupenic states of K+ depletion and acidosis. Thus the summation of the observed chemical and electrical driving forces between the cellular and luminal compartments could quantitatively account for the passive entry of K+ into the lumen of the distal tubule under the different metabolic states.

Descending pathways in the cervical cord of cats affecting blood pressure and sympathetic activity

Abstract: In 13 cats spinalized at C2 the cervical spinal cord (SC) was explored systematically by electrical monopolar stimulation (40 μA or 50 μA) for responses of blood-pressure (BP) and sympathetic activity (renal or splanchnic). Sympathetic responses and BP reactions were elicited from extensive regions of the SC. Stimulation within the dorsal column changed neither BP nor sympathetic mass activity (SMA).

Metabolism of canine kidneys in anaerobic ischemia and in aerobic ischemia by persufflation with gaseous oxygen.

Abstract: The changes in the status of the adenylic acid-creatine phosphate system and in glycogen, glucose, and lactate were investigated in canine kidneys during preservation in anaerobic and aerobic ischemia at normo- and hypothermia. For anaerobic ischemia, the kidneys were stored without additional measures; for aerobic ischemia, the ischemic kidneys were persufflated with gaseous O2 or gas mixtures containing O2 via the renal artery or vein (orthograde and retrograde aerobic ischemia respectively). Prior to preservation, the kidneys were flushed with cell-free perfusates. Changes in the metabolic status characteristic of anaerobic ischemia were a decrease in the tissue levels of ATP, creatine phosphate, glycogen, glucose, and the sum of adenine nucleotides, a transitory increase in ADP and AMP, and an increase in the tissue level of lactate. Hypothermia caused a retardation of the anaerobic alterations; the loss of ATP was slowed down by factors of 2 and 9.5 when the temperatures were lowered from 37° to 26° and 6°C, respectively. In aerobic ischemia with orthograde and retrograde persufflation of 100% O2 (persufflation pressure = PP 60 and 30 mm Hg), deviations from a regular metabolic status developed very slowly. While the ATP-level decreased to 50% of the control value within scarcely 30 min of anaerobic ischemia at 6°C, it was almost 48 h before a similar loss of ATP occurred during orthograde aerobic ischemia at 6°C. Reduction of O2 in the persufflation gas to 40 and 21 vol-% resulted in less adequate preservation of the metabolic status. Increasing PP to 100 mm Hg for orthograde persufflation had no effect. An increase in PP to 60 mm Hg for retrograde persufflation resulted in a further delay in the metabolic deterioration. The long-term preservation of a regular metabolic status or the slow deviation of the metabolic pattern from the normal range during ischemia with O2-persufflation indicates a significantly smaller energy deficit than during storage in anaerobic ischemia. It must be attributed to a sufficient aerobiosis in the aerobically ischemic kidney, during which organogenic substrates brought in by the initial perfusion are utilized.

The isolated frog skin epithelium: presence of alpha and beta adrenergic receptors regulating active sodium transport and water permeability.

Abstract: The effects of stimulation of α and β adrenergic receptors on short circuit current (S.C.C.), Na+ and Cl− fluxes and osmotic water permeability were studied on isolated frog skin epithelial layers separated from the dermis. Low norepinephrine doses (final concentrations in the incubation medium ranging from 5×10−9 to 10−8 M) produced increased water permeability and S.C.C. The latter was entirely accounted for by an increase in the active Na+ influx. Na+ outflux and Cl− fluxes were not modified. Both these effects disappeared after treatment with the β blocking agent, Propranolol. Higher norepinephrine doses (final concentrations: 10−7 to 10−6 M) produced: 1. an increase in water permeability lower than that produced by low doses, the highest doses failing to increase water permeability, and 2. a triphasic change in S.C.C.: after an initial increase, S.C.C. dropped to its resting value and then rose again to a sustained value. Na+ and Cl− flux measurements showed that the variation in S.C.C. reflected variations in active Na+ transport. When the same high norepinephrine doses were applied after treatment with the α blocking agent Phentolamine, the effects observed were identical to those obtained with low doses. On β blocked preparations, large doses of norepinephrine inhibited the water permeability and sodium transport increases induced by theophylline or oxytocin but did not modify those induced by 3′5′-cyclic AMP. The inhibition was suppressed after blocking α receptors. From the foregoing, it was concluded that both α and β adrenergic receptors are present in frog skin epithelial cells and are involved in the regulation of water and sodium permeability. It is suggested that the inhibitory effect of α stimulation resulted from the inhibition of cyclic-AMP generating system, the activity of which is under the positive control effect of oxytocin and β stimulation.