Showing papers in "Pflügers Archiv: European Journal of Physiology in 1970"

The composition of fluid collected by micropuncture and catheterization from the seminiferous tubules and rete testis of rats

Abstract: Fluid and electrolyte secretion in the rat testis has been studied by micropuncture and catheterization. Three fluids have been collected and analyzed: 1. Rete-testis fluid, obtained by catheterization of the rete testis. 2. Free-flow fluid, obtained by micropuncture of seminiferous tubules. 3. Primary fluid, also obtained by micropuncture but after first filling a tubule segment with oil and allowing new secretion to form and break up the oil column into droplets.

Regulation of superficial nephron filtration rate by tubulo-glomerular feedback

Abstract: Possible regulation of glomerular filtration rate by tubulo-glomerular feedback from a late tubular site was studied in microperfusion experiments on rats. During perfusion of loops of Henle with varying flow rates and different perfusion solutions, filtration rate of the perfused nephrons was measured by total proximal fluid collection and inulin determination. During perfusion with isotonic Ringer's solution nephron filtration rate decreased significantly with increasing perfusion rates. Since proximal intratubular pressure was experimentally kept constant, this response must reflect decreased glomerular capillary pressure. Increasing the flow rate during perfusion with isotonic sodium sulfate or mannitol solutions was not associated with significant changes of filtration rate. Thus some correlate of the flow rate of normal loop of Henle fluid can affect filtrate formation. Such an effect may be mediated by the juxtaglomerular apparatus. Our results are consistent with the concept that the triggering signal is a function of the amount of distal sodium that is able to permeate the cell membrane at the receptor site rather than of distal intratubular sodium concentration.

Micropuncture evaluation of the importance of perivascular pH for the arteriolar diameter on the brain surface

Abstract: A micropipette technique was used to induce local changes of the bicarbonate concentration of the cerebro-spinal fluid surrounding arterioles on the exposed cerebral cortex of anaesthetized rats and cats. Injection volumes of a few nanoliters caused circumscribed and pronounced changes of the diameter of the arterioles under study: mock spinal fluid without bicarbonate dilated, while a solution containing 25 meq/l of bicarbonate constricted the vessels. In such experiments the localpCO2 of the arteriolar wall remains practically constant, since it is set by thepCO2 of the arterial blood and of the cerebral tissue. Hence the microinjections essentially consisted in a local change of the pH of the fluid surrounding a small segment of a cerebral arteriole. Since metabolic changes of the nervous tissue changes the periarteriolar pH, it is probable that local pH induced vasomotor changes of the type reported here participate in the so called metabolic regulation of the cerebral blood flow which underlies the local adaptation of the cerebral blood flow to changing functional demands.

Two modes of Na extrusion in cells from guinea pig kidney cortex slices.

Abstract: Cells from guinea pig kidney cortex slices, which have been loaded with Na and caused to lose K, by leaching at 0.6° C for 2.5 hours, extrude Na with Cl upon rewarming to 25° C in a medium without K. A subsequent rise in the K concentration in the bath at 25° C induces further net Na extrusion, 1 Na being extruded in exchange for 1 K that is taken up. When the leached tissue is rewarmed to 25°C in the presence of K in the bathing fluid (2 or 16 mM), some Na is extruded accompanied with Cl (by a mechanism that is inhibited by ethacrynic acid) and some Na is extruded maintanining a 1:1 ratio with the K that is taken up, (this system being inhibited by ouabain). Thus two modes of Na extrusion are observed, mode A that is accompanied by net Cl efflux, and that is inhibited by 2 mM ethacrynic acid, but not by 1 or 10 mM ouabain and mode B in which one K is taken up for each Na extruded. Mode B is inhibited by 1 mM ouabain and not by ethacrynic acid. DNP and anoxia inhibit both modes A and B. Insufficient doses of ouabain do not explain the refractoriness of mode A to ouabain. Ouabain and ethacrynic acid are known inhibitors of the Na−K-ATPase at much lower doses. It is concluded that both modes may originate in different Na pumps which may have different energy sources. Pump A should be efficient in the volume regulation of the cell. According to experimental procedure, both modes of Na extrusion appear of comparable magnitude. In the steady-state their relative role may be different.

The slow inward current and the action of manganese ions in guinea-pig's myocardium.

Abstract: In guinea-pig's myocardium the slow inward current, which seems to be related to the positive plateau of the myocardial action potential, was studied by voltage clamp technique. This current could be displayed when the initial rapid inward current was inactivated by shifting the holding potential to levels positive to the resting potential. The threshold potential for the slow inward current was about −40 mV and the current was maxium at depolarizations to between −10 mV and +10 mV. The reversal potential was about +70 mV. A similar slow inward current was obtained when the preparation was bathed either in a sodium-free solution which contained calcium ions or in a calcium-free solution which contained sodium ions. In the latter solution, the reversal potential was between +30 mV and +50 mV. It seems possible that not only calcium but also sodium ions contribute to the slow inward current in normal Tyrode's solution. Manganese ions in concentrations of 5–20 mM depressed the slow inward current, especially when the depolirizations were small. In a calcium-free solution, the amplitude of the slow inward current flowing during large depolarizations was increased by manganese ions. In a calcium and sodium-free solution, a slow inward current was obtained when manganese ions were present.

The cochlear potentials. II. The nature of the cochlear endolymphatic resting potential.

Abstract: The effect, on the endocochlear resting potential (ERP) of anoxemia, cyanide, pH changes and changes of the electrolyte composition of the perilymph was studied.

Micropuncture study of handling of phosphate by proximal and distal nephron in normal and parathyroidectomized rat. Evidence for distal reabsorption.

Abstract: The handling of phosphate by the nephron of the rat was investigated by proximal and distal tubular micropunctures in three experimental conditions: 1. in normal animals, 2. several days after parathyroidectomy (“chronic”) and 3. immediately after parathyroidectomy (“acute”). In proximal tubules of normal animals phosphate reabsorption appears to be gradient limited. The concentration gradient is already reached in the early proximal. Consequently, proximal phosphate reabsorption is almost completed in this segment. Moreover, reabsorption is higher in early proximal in normal than in acute although the reverse is observed at the late accessible proximal. This indicates that the initial part of the proximal nephron in normal has an increased capacity to reabsorb phosphate. Comparison of phosphate delivery at early distal and late proximal tubule suggests that, in normal and chronic, phosphate reabsorption either stops in the pars recta or is compensated by a net addition. Phosphate delivery is higher in superficial distal tubules than in ureteral urine, which is interpreted as a phosphate reabsorption by the terminal nephron since the heterogeneity of the nephrons population cannot explain the results. There are several arguments suggesting that this reabsorption is an active process. Moreover it appears to be inhibited by PTH.

Antagonistic changes of blood flow and sympathetic activity in different vascular beds following central thermal stimulation

Abstract: Blood flow in arteries mainly supplying cutaneous, muscular or intestinal vascular regions and aortic blood flow were measured with an electromagnetic flowmeter in anesthetized dogs immobilized with succinyl choline. Up to 3 flows were recorded simultaneously with mean arterial pressure during thermal stimulation of the spinal cord at constant, neutral ambient air temperatures. In conformity with earlier observations, skin blood flow increased during moderate and strong spinal cord heating and was reduced during spinal cord cooling. Conversely, intestinal blood flow decreased during heating in all experiments and increased during cooling in 5 out of 10 experimental animals. Aortic blood flow and muscle blood flow did not change substantially during either heating or cooling. Arterial pressure showed a moderate rise during strong heating, but was not influenced by cooling and moderate heating. The changes of blood flow distribution observed in the experiments are in keeping with results obtained under external thermal stimulation. It is assumed that the antagonistic changes of blood flow in the cutaneous and intestinal vascular beds were induced by antagonistic changes of sympathetic vasoconstrictor activity.

The cochlear potentials. I. The effect of ouabain on the cochlear potentials of the guinea pig.

Abstract: SummaryThe effect of ouabain on the endocochlear resting potential (ERP) and cochlear microphonic potential (CMP) was studied by continuous perfusion of the perilymphatic space with ouabain in Krebs-Ringer solution.Ouabain caused a concentration-dependent depression of both ERP and CMP. A striking similarity was found in thepI50 (5.4–5.5) for both ERP and CMP and the Na+-K+-ATPase activity in the stria vascularis.It was concluded that the ERP is generated by the Na+-K+-ATPase system in the stria vascularis. The CMP appears to depend strongly on the ERP, although a contribution of the DC potential of the cells of the organ of Corti seems likely.

Efferent influence on the vestibular organ during active movements of the body

Abstract: In the goldfish one can induce optokinetic turning motions with a stimulus consisting of a pattern of moving stripes. These movements are active movements, performed freely by the fish. In the experiments reported here, recordings were made from the primary afferent fibers of the horizontal semicircular canal of relaxed (Flaxedil) goldfish. Although the fish remained completely motionless because of the relaxation, the activity of the nerve fibers under investigation changed when a moving pattern of stripes was shown. Depending on the direction of the moving pattern the activity decreased or increased. To explain this it is assumed that the optokinetic stimulus induces an intention in the fish to move, which the fish is not able to perform when relaxed. In conjunction with the command to move, it is further assumed that the sensitivity of the receptors in the vestibular organ is shifted by means of efferent innervation. This shift would keep the afferent activity constant during the actual performance of active body motions. Since the body movement does not occur during relaxation, one can observe a change in the afferent activity. The physical stimulus on the vestibular organ during active body movements would be compensated for by this mechanism, so that the organ would still be completely capable of responding to any additional stimulus (passive body movements, disturbances of equilibrium).

Competitive Inhibition of Phlorizin Binding by D-Glucose and the Influence of Sodium: a Study on Isolated Brush Border Membrane of Rat Kidney*

Abstract: Glucose binding to the luminal cell membrane was studied in the isolated brush border of rat renal cortex by means of inhibition of phlorizin binding to a specific receptor site. This effect was reversible and stereospecific and fulfilled the criteria of fully competitive inhibition. Thus, the kinetic parameters ofd-glucose binding to the same receptor could be derived. The affinity of the receptor to either substrate, phlorizin as well asd-glucose, increased with rising ambient sodium concentration while the number of binding sites remained unchanged. Other cations (K+, Ca++, Mg++) showed no effect on either parameter. The results of this study are in agreement with a model of transmembrane transport of glucose put forward by Crane.

Electrical and mechanical responses from ventricular muscle fibers after inactivation of the sodium carrying system.

Abstract: The electrical and mechanical responses of spontaneously and KCl depolarized ventricular fibers (cat and dog) were studied using a modified sucrose gap technique. The following observations were made:

Antagonistic changes of blood flow and sympathetic activity in different vascular beds following central thermal stimulation. II. Cutaneous and visceral sympathetic activity during spinal cord heating and cooling in anesthetized rabbits and cats.

Abstract: SummaryIn anesthetized rabbits and cats immobilized with succinyl choline, the discharges of sympathetic efferents supplying cutaneous and visceral regions were simultaneously recorded. The effect of thermal stimulation of the spinal cord on regional sympathetic activity was tested on the basis of the integrated discharges.During spinal cord heating cutaneous sympathetic activity decreased, while visceral sympathetic activity increased at the same time. During cooling the reverse reaction, i.e. increase of activity in cutaneous and decrease in visceral sympathetic efferents, was observed. This antagonistic behaviour of cutaneous and visceral efferent activity was found in all rabbits and in about half of the investigated cats.The changes of cutaneous efferent activity were in keeping with the thermoregulatory changes of cutaneous blood flow following thermal stimulation of the spinal cord. The changes of visceral sympathetic activity offer an explanation for the adjustments of intestinal blood flow observed under the same central thermal stimulus.It is suggested as a working hypothesis that the sympathetic nervous system may perform under special conditions a sort of “reciprocal innervation” of functionally antagonistic autonomic effector systems.

Effect of amiloride on sodium transport in frog skin. II. Sodium transport pool and unidirectional fluxes.

Abstract: The effect of Amiloride on several parameters of sodium transport was investigated on the isolated frog skin. Amiloride at a concentration of 10−4 M/l decreased the sodium concentration in the sodium transport pool from 8.9 meq/kg cell water to 3.7 meq/kg cell water. No effect was observed on the intracellular sodium which is exchangeable from the corium side. Short circuit current and unidirectional sodium influx were diminished to the same extent whilst the unidirectional sodium efflux was not affected. In contrast to the short circuit current, which reaches a new steady state value within seconds, the unidirectional sodium influx reaches its new steady state with a half-time of 3.3 min. From the difference in the time courses of the decreases of short circuit current and unidirectional sodium influx, an amount of sodium could be calculated which agreed well with the directly measured fall in the sodium transport pool.

Voltage and Time Dependence of Excitatory Sodium Current in Cooled Sheep Purkinje Fibres

Abstract: Very small Purkinje fibre preparations were cooled down to 4–5°C in order to slow the activation of the excitatory sodium current to such an extent that the latter could be separated from the capacitive membrane current. Although the resting potential of the membrane decreased to −30 mV at the low temperature, it was possible to trigger the sodium carrying system by conditioning the membrane with hyperpolarizing pulses applied under voltage clamp conditions. The sodium currents flowing after sudden depolarizations starting from various conditioning prepotentials and going to various clamp potentials were analyzed according to the Hodgkin-Huxley equations. It turned out that the results could be satisfactorily fitted by the equations, although the absolute values and the potential dependences of the rate constants differed from those found for the squid giant axon in a characteristic manner. Particularlyh, the variable describing the inactivation of the sodium carrying system, had a remarkable potential dependence at the low temperature extending from unity at a potential as high as −180 mV to zero at a potential −100 mV. The time course of the removal of inactivation showed a similar dependence on conditioning prepotential and time to that found for the squid giant axon. Conditioning pulses of up to 10 s were necessary to remove inactivation at a prepotential of −110 mV. The decay of the sodium current flowing after depolarizations from various conditioning prepotentials to the same clamp potential differed from that of the squid axon in a way that it could better be fitted by two time constants rather than one. By comparison of the data with those obtained from experiments carried out at 20°C extrapolations of the results to body temperature were made. These suggest that at 37°C the sodium carrying system should be almost entirely inactivated when the action potential reaches its crest.

Zur Zeitgeber-Stärke eines Licht-Dunkel-Wechsels für die circadiane Periodik des Menschen

Abstract: Die circadiane Periodik von 8 Versuchspersonen wurde in strenger Isolation unter dem Einflus eines kunstlichen Licht-Dunkel-Wechsels mit einer Periode von 24 Std untersucht. Keine der Versuchspersonen war mit dem Zeitgeber synchronisiert, vielmehr zeigten alle eine autonome (freilaufende) Periodik. Im Gegensatz hierzu waren alle 16 Versuchspersonen, die unter dem Einflus eines gleichen Licht-Dunkel-Wechsels lebten, der aber durch Gong-Signale in regelmasigen Abstanden erganzt wurde, mit dem Zeitgeber synchronisiert; die Versuchspersonen waren dabei angewiesen, bei jedem Gong-Signal eine Urinprobe zu liefern und einige Tests zu absolvieren.

Electrical properties and synaptic connections of the sympathetic neurons in the rat and guinea-pig superior cervical ganglion

Abstract: Features of action potentials and synaptic potentials as obtained by intracellular recordings from the sympathetic ganglion cells in the superior cervical ganglion of both the rat and the guinea-pig are described. Time-constant, imput resistance and capacitance of the ganglion cell membrane were also measured. Rheobasic currents and chronaxies are evaluated from strength-latency recordings. Single stimulating shocks applied to pre-ganglionic fibres produce repeated activation in the sympathetic ganglion cells and neuron response appear to be dispersed over a considerable length of time. Simultaneous recordings of extracellular post-ganglionic discharge and intracellular response from single ganglion units showed that pre-ganglionic fibres with different conduction velocities converge on the neurons. This convergence can fully justify the temporal dispersion of the ganglion cell responses.

Thermoregulation during fever: Change of set-point or change of gain

Abstract: Thermoregulation during fever is generally described in terms of a change in the level of the reference signal in the control system. This paper presents an alternative postulate, namely that during fever the thermoregulatory control centre undergoes a pyrogen-induced change in sensitivity, or gain. This postulate is supported strongly by the behaviour of thermoregulatory neurones. Febrile and afebrile thermoregulation can be described by means of a model with no reference signal at all, but with opposing warm and cold stimuli to the control centre.

Free flow micropuncture studies of glucose transport in the rat nephron.

Abstract: Tubular free flow micropuncture studies were done in normoglycemic rats to evaluated-glucose handling along the nephron. 1. A rapid removal of filtered glucose occured over the first three millimeters of the proximal tubule. 2. The intratubular glucose concentration remained constant at 0.25±0.20 mmol/l (SD) over the second half of the accessible proximal tubule. This value is similar to one predicted on the basis of kinetic data obtained previously under conditions of zero volume flux. 3. More than 98 per cent of the filtered glucose was reabsorbed by the proximal tubule. 4. No further net flux was detectable between the proximal segment and the end of the distal tubule accessible to micropuncture. 5. The collecting duct reduced glucose excretion to less than 0.1 per cent of the filtered load. The final rate of glucose excretion was independent of the rate of urine flow.

Activity in single hypoglossal fibers during cortically induced swallowing and chewing in rabbits.

Abstract: In rabbits under light ether anesthesia, rhythmic movements of chewing and swallowing were produced by stimulation to the antero-lateral cortex. The activity of hypoglossal motor fibers during such stimulation was studied, together with changes evoked by stimulation of the superior laryngeal nerve. 1. Most hypoglossal motor fibers discharged bursts of impulses in phase with the cortically evoked rhythmic chewing, the majority being concurrent with jawclosing. Among these, some units fired with fairly constant latency after each stimulus, while others had no consistent relation to the stimuli in the train. A few units bore no relation to the rhythm of chewing in their discharge of impulses, either following regularly to each stimulus or occurring sporadically. 2. In the hypoglossal units discharging grouped impulses in phase with chewing, some displayed also a characteristic burst, whereas others ceased discharging momentarily when a swallow occurred during cortical stimulation. 3. The shortest time for cortico-hypoglossal conduction ranged from 5.8 to 12.0 msec, indicating polysynaptic linkage for the path. 4. Cortically evoked rhythmic chewing was arrested by stimulation of the superior laryngeal nerve. During this period, one group of hypoglossal units ceased discharging completely, while others discharged impulses regularly after each stimulus pulse. 5. Motoparalysis did not alter the pattern of discharge of the hypoglossal nerve fibers by cortical and/or superior laryngeal stimulation, though abolishing totally the movement of chewing and swallowing. 6. The relevance of these findings to the central neural arrangement for the control of rhythmic chewing and swallowing is discussed.

Interaction of baroreceptor afferents from carotid sinus and aorta at the nucleus tractus solitarii.

Abstract: In chloralose-urethane anaesthetized cats, low-threshold baroreceptor afferents of the carotid sinus and aortic nerves were stimulated electrically. Evoked responses were recorded within the nucleus tractus solitarii near the obex. At a certain electrode position in this area an evoked potential (E. P.) was elicited by stimulation of the homolateral carotid sinus or aortic nerve as well as the contralateral sinus or aortic nerve. At this site an interaction of these four baroreceptor nerves was demonstrated by testing the E. P. of one nerve after a conditioning stimulation of another nerve. Simultaneous E. P.'s did not show arithmetical summation. A strong reduction of the test-E.P. (mean value of reduction: 50%) occurred with a conditioning-testing interval of 10–20 msec. The test-E. P. came back to the control amplitude at an interval of 100–150 msec. Neither picrotoxin nor strychnine changed the time course or extent of these interactions. It was further observed that the most effective conditioning-testing interval for inhibition of test response corresponded closely to the difference between the arrival times of arotic and sinus nerve activities evoked by the cardiovascular pulse (aortic 16±5 msec before sinus nerve).

The course of inhibition of sympathetic activity during various patterns of carotid sinus nerve stimulation.

Abstract: In 63 chloralose-urethane anaesthetized dogs both carotid sinus nerves (CSN) and cervical vagal nerves were cut and the sympathetic activity was recorded. During bilateral CSN-stimulation for 2 min the following pattern of sympathetic inhibition was observed:

Increase of sodium concentration near the inner surface of the nodal membrane.

Abstract: Voltage-clamp experiments have been performed in order to investigate the after effects of Na-accumulation in myelinated nerve fibres from the frogRana esculenta. 1. The ionic current associated with a depolarizing test-pulse adjusted to the sodium equilibrium potential has been measured following conditioning volleys of depolarizing pulses. 2. A marked shift ofENa towards less positive potentials has been observed following volleys of more than 50 msec; the time course of recovery ofENa showed a rapid phase followed by a slow one. Both phases proved to be insensitive to suabain, DNP and K-free solution. The slow recovery phase was, however, very much prolonged when the conditioning volleys were applied to a node superfused with Li-Ri. 3. The shift ofENa was associated with a drastic reduction of the outward potassium current and with anomalous rectification; the reduction of the potassium outward current, however, was observed when both the sodium and potassium ions moved from inside to the external solution. 4. The results may be explained by an influx of sodium ions into the nerve fibre which are temporarily accumulated near the inner surface of the membrane. They compete with potassium ions at the inner opening of the potassium “channel” and thereby reduce the number of potassium ions which are available to move through the membrane under the influence of the electrochemical gradient.

Diffusion error and specific consumption of the Pt electrode during pO2 measurements in the steady state

Abstract: Im steady state beeinflussen Diffusionsfehler und Eigenverbrauch der Pt-Elektrode als systematische Fehler O2-Partialdruckmessungen. Sie sind abhangig von den geometrischen Eigenschaften der Elektrode, den Diffusionseigenschaften der Membran sowie den Diffusions- und Konvektionseigenschaften des Mesmediums. Das Diffusionsfeld vor der Pt-Oberflache und das dadurch bestimmte stationare Messignal werden fur gasformige und nicht gasformige Medien mit und ohne Konvektion berechnet. Daraus resultieren quantitative Aussagen uber die systematischen Fehler. Speziell fur Messungen in durchbluteten Geweben (z. B. Hirnrinde und Myokard) wird der Einflus des Eigenverbrauchs von Pt-Elektroden auf den intracapillarenpO2-Abfall in Durchblutungsrichtung und das intercapillarepO2-Feld am Mesort der Elektrode ermittelt. Diese Berechnungen erfolgten mit Hilfe eines Digitalmodells.

Single unit responses in the cervical sympathetic trunk upon somatic nerve stimulation.

Abstract: 1. In cats anesthetized with chloralose single unit activity was recorded from filaments of the cervical sympathetic trunk dissected caudal to the upper cervical ganglion. The characteristics of the spontaneous and evoked spike discharges of these preganglionic units upon somatic nerve stimulation were studied. The vagus and carotid sinus nerves were cut. 2. More than 500 units were identified. Their conduction velocities ranges from 20 m/s to less than 0.5 m/s. The units with conduction velocities below 2 m/s (28% of our sample) were considered to be unmyelinated fibers. The peak of the conduction velocity histogram of the myelinated fibers was at 4–6 m/s. 3. Both in the myelinated and in the unmyelinated fiber range mainly two types of sympathetic units were found: about 70% were not spontaneously active and did not exhibit evoked discharges, whereas 25% had both properties. The other 5% had either one or the other property. 4. As a rule the evoked response of a unit consisted of one spike only. More rarely units with 2–4 evoked discharges per stimulus were seen. In any given unit the evoked discharges occurred with a certain propability, which, for the majority of units, was between 40–60% in a series of 20 trials. 5. The sympathetic units responded either to cutaneous volleys, or to cutaneous and muscle volleys. No units were seen which responded to a muscle afferent volley but not to a cutaneous one. 6. The spontaneous activity was of low frequency. In the myelinated fiber range the average was 1.7 Hz. In the unmyelinated fiber range an average of 2.9 Hz was found. Following somatic nerve stimulation the spontaneous discharge was reduced or abolished for periods up to 1 s independent of the occurrence of an evoked response. The maximum depression appeared immediately after the onset of the inhibition.

Isolated toad skin epithelium: transport characteristics.

Abstract: A procedure that allows areas up to 1 cm2 of the epithelium to be separated from the corium of the toad skin is described. For several hours the preparation maintains the transport characteristics of the isolated intact skin, namely electrical potential differences up to 100 mV (outer side negative) and short-circuit currents up to 80 μAmp/cm2, which are equal to the net Na fluxes. The isolated epithelium responds well to antidiuretic hormone. Microelectrode impalement is easier than in the intact skin. The most negative stable electrical potential level within the epithelium is recorded immediately below the first corneal layer, at 5–15 μ from the outer surface. From that site outwards, the highest epithelial resistance is measured across structures that are mainly Na-permeable and less K-permeable and which repsond to ADH with a diminution of their resistance. The structures located from that site inwards (the internal 30–40 μ of the epithelium) are highly permeable to K. The region of high K permeability does not seem to be localized at only one site near the basement membrane, but distributed across several cell layers of the deeper strata.

Simultaneous measurement of unidirectional and net sodium fluxes in microperfused rat proximal tubules

Abstract: Microperfusion experiments were performed on oil-blocked tubules in non diuretic Rats, using either isotonic NaCl, or “equilibrated” solutions; perfusion rates ranged from 20 to 40 nl/min. Several recollections were made from each perfused tubule after changing either the perfusion rate or the collection site. Net fluxes of water and sodium were calculated from changes in3H-Inulin and Na+ concentrations. Unidirectional sodium efflux was calculated from22Na specific activity change. Appropriate equations were derived to account, when necessary, for the change in flow rate along the perfused tubule.

Effect of Amiloride on sodium transport of frog skin. I. Action on intracellular sodium content.

Abstract: ZusammenfassungDie Wirkung von Amilorid auf den Natriumgehalt der isolierten Froschhaut wird untersucht. Bei Inkubation in Amilorid-haltiger Ringer-Lösung (10−4 M/l, 15 min Inkubationszeit) vermindert sich die intracelluläre, mit Isotopen austauschbare Natriumkonzentration um ca. 10 meq/kg Zellwasser. Der Effekt ist maximal bei Amiloridkonzentrationen zwischen 0,3 und 1,0·10−4 M/l und Inkubationszeiten zwischen 6 und 15 min. Der nicht mit Isotopen austauschbare Natriumanteil bleibt unter allen Bedingungen konstant. Wassergehalt, extracelluläres Volumen und intracelluläre Kaliumkonzentration werden durch Amilorid nicht beeinflußt. Der Kurzschlußstrom erreicht einen neuen steady state-Wert innerhalb von Sekunden nach Zugabe von Amilorid zu der epithelseitigen Badelösung.Es wird geschlossen, daß Amilorid nur ein Natriumtransportkompartment beeinflußt, welches etwa 10% des austauschbaren intracellulären Natriums enthält.SummaryThe effect of Amiloride on intracellular sodium content of the isolated frog skin was investigated. The maximal effect on intracellular exchangeable sodium concentration (−10 meq/kg cell water) was found at concentrations of Amiloride in the incubation solution between 0.3 and 1.0×10−4 M/l, and at an incubation time of 6–15 min. Since total intracellular sodium concentration is also reduced by approximately 10 meq/kg cell water, it follows that the intracellular non-exchangeable sodium concentration was not affected by Amiloride. Water content, extracellular volume, and intracellular potassium concentration remained constant. The short circuit current reached a new steady state within a few seconds after addition of Amiloride. It is concluded that Amiloride affects a sodium transport pool, which contains about 10% of the exchangeable intracellular sodium.

A microperfusion investigation of bicarbonate secretion by the rat submaxillary gland. The action of a parasumpathomimetic drug on electrolyte transport.

Abstract: Bicarbonate transport in the rat submaxillary main duct has been studied by microperfusion. Bicarbonate was concentrated in the duct lumen against an electrochemical gradient and the equilibrium concentration was estimated to be 56.5 mEq/l±3.1 (S.E.M.,n=11). The secretory mechanism could not be inhibited by 6 mMolar cyanide although such concentrations caused marked inhibition of both net sodium efflux and net potassium influx. Bicarbonate secretion in the main duct was not inhibited by acetazolamide whether applied from the duct lumen or given intravenously. Similarly, the drug was without effect on bicarbonate excretion by the intact gland even when maximum excretory rates had been induced with carbachol. It was concluded that catalytic hydration of carbon dioxide to carbonic acid was not a rate-limiting step in the bicarbonate secretory process. The data did not permit a distinction to be made between a bicarbonate secretory processper se and a process of either H+ reabsorption or OH− secretion. The parasympathomimetic agent, carbachol, when given parenterally was found to increase sharply the net influx of bicarbonate into the microperfused main duct as well as to reduce net sodium efflux and net potassium influx. Previously it had been postulated that final saliva was formed in two stages. First a plasma-like primary secretion was formed at a rate depending on the degree of stimulation, and second, the primary secretion was modified in the gland duct system by reabsorptive and secretory processes whose transport rates were presumed to be independent of the degree of stimulus. It now becomes necessary to postulate that stimulation can act on electrolyte transport at both primary and secondary levels; at present, however, no data are available to show whether appreciable net water influx can ever occur at the secondary level.

Elektrophysiologische Untersuchungen zur normalen Spontanaktivität der isolierten Taenia coli des Meerschweinchens

Abstract: Die Spontanaktivitat der isolierten Taenia coli des Meerschweinchens wurde mit verschiedenen Methoden registriert: extracellulare Messung der elektrischen Aktivitat mit Pt-Elektroden sowie mit der Saccharosetrennwand-Technik; intracellulare Potentialmessung mit Glas-Mikroelektroden; Messung der mechanischen Aktivitat unter isometrischen, isotonischen und auxotonischen Bedingungen. Die normale Spontanaktivitat ist stets durch langsame Fluktuationen mit einer Periodendauer von 1–3 min gekennzeichnet. Auch in situ zeigt die Taenia coli diese “Minuten-Rhythmik”, wie Messungen mit implantierten Elektroden ergeben haben. Bei stark gedehnten und sehr kurzen Praparaten (unter 5 mm) erlischt die Minuten-Rhythmik in der Regel und gibt einer kontinuierlichen Dauerentladung von Spikes Raum. Dies ist offenbar der Hauptgrund dafur, das in den meisten neueren Untersuchungen an der Taenia coli die Minuten-Rhythmik nicht beobachtet worden ist. Viele Einflusse auf die Spontanaktivitat der Taenie mussen unter Einbeziehung der Minuten-Rhythmik neu uberpruft werden. Die Gliederung der verschiedenen rhythmischen Erscheinungen an der Taenie wird diskutiert.