Showing papers in "Pflügers Archiv: European Journal of Physiology in 1968"

Micropuncture studies on the filtration rate of single superficial and juxtamedullary glomeruli in the rat kidney.

Abstract: Single nephron filtration rates of superficial and juxtamedullary nephrons were determined in high and low sodium rats. Single nephron GFR was calculated from TF/P inulin and tubular flow rate in superficial nephrons and single juxtamedullary GFR from corresponding data in long loops of Henle. In low sodium rats superficial nephron GFR was 23.5±6.4 (SD)×10−6 ml/min×g KW, juxtamedullary nephron GFR was 58.2±13.6 and total kidney GFR (C In) was 0.94±0.16 ml/min×g KW. Using these single nephron values, total kidney GFR and a total number of 30,000 glomeruli per kidney, the number of superficial and juxtamedullary glomeruli was calculated to be 23,267 and 6,733, respectively. During high sodium diet superficial nephron GFR increased to 38.1±11.3 and single juxtamedullary GFR decreased to 16.5±6.6, total kidney GFR increasing to 1.01±0.24. Calculation again revealed the same distribution of the two nephron types. End-proximal TF/P inulin in superficial nephrons was 2.36±0.36 in low sodium and 2.31±0.28 in high sodium rats. Loops of Henle TF/P inulin and intratubular flow rate were inversely related: the highest TF/P inulin values and lowest intratubular flow rates were found in the descending limb. These data quantify the distribution of superficial and juxtamedullary nephrons on a functional basis and suggest a mechanism by which the kidney adjusts sodium excretion by altering the contribution of each nephron type to total kidney GFR.

The importance of the perfusion pressure in the coronary arteries for the contractility and the oxygen consumption of the heart.

Abstract: The influence of increasing perfusion pressure in the coronary arteries on cardiac contractility and oxygen consumption was studied in isovolumetrically working, empty beating, and potassium arrested guinea-pig hearts. Raising the coronary perfusion pressure from 60 to 80 cm H2O increased left ventricular peak systolic pressure by 19.4±2.8%, coronary flow by 47.7±8.0% and oxygen consumption by 32.7±6.2% (N=17). At a constant perfusion pressure hypoxia increased the coronary flow by 111.8±16.4% (N=19), but did not alter the contractility of the heart or its oxygen consumption. Increasing pressure without changing flow, raised pressure in the left ventricle by 26.5±4.8% and myocardial oxygen consumption by 20.3±3.4% (N=14). The end-diastolic pressure and the heart rate remained unchanged in all experiments. From these findings it may be concluded that the pressure in the coronary vessels — independent of the flow rate — exercises a positive inotropic effect, thereby increasing metabolism. This can be explained by increased fibre tension, caused by an extension of the coronary vessels, the so-called “garden-hose-effect”.

The effect of the duration of the action potential on contraction in the mammalian heart muscle

Abstract: A method is described to control the membrane potential in preparations of mammalian myocardium, and to measure tension simultaneously. The following observations are made: A discussion of the relationship between the action potential and contraction in cardiac muscle is included.

Voltage clamp experiments on frog atrial heart muscle fibres with the sucrose gap technique.

Abstract: Voltage clamp experiments with the double sucrose gap technique performed on frog heart atrial trabecles show: These results confirm the findings of McAllister and Noble (1966, 1967) concerning the existence of a delayed rectification in cardiac muscle fibres With respect to the sodium system they are to a certain extent in agreement with the ones of Giebisch and Weidmann (1967) and with the hypothesis of Brady and Woodbury (1960) They can qualitatively explain the time course of the action potential

The diameter of the intact carotid artery in man and its change with pulse pressure

Abstract: The pressure-diameter relationship of the intact human common carotid artery was studied in 9 healthy subjects ranging in age between 24 and 34 years. The diameter of the carotid artery was measured with an ultrasound-echo ranging device. The following results were obtained: The data suggest that one has to be cautious when applying results from exposed or isolated arteries to the intact circulation.

Die Wirkung von Skorpiongift auf die Ionenströme des Ranvierschen Schnürrings

Abstract: 1. Die Wirkung von Skorpiongift auf die Inaktivierung der Natrium-PermeabilitatPNa wurde in voltage-clamp-Experimenten an einzelnen markhaltigen Nervenfasern von Xenopus laevis untersucht. 2. Beim normalen Ruhepotential warPNa der vergifteten Membran starker inaktiviert als an der unvergifteten Membran; bei starken Depolarisationen war die Inaktivierung jedoch unvollstandig. 3. Der zeitliche Verlauf vonPNa konnte unter verschiedenen experimentellen Bedingungen mit den Hodgkin-Huxley-Gleichungen beschrieben werden, die wie folgt modifiziert wurden:

The mechanism of action of amipramizide.

Abstract: Amipramizide is capable of inhibiting active sodium transport by isolated bladder, colon and skin of the toad,Bufo marinus, when added in small amounts (⩽10−5 M) to the solution coming in contact with the outer surface of the preparations. Inhibition occurs rapidly, is proportionate to dose and is reversible. No significant effect results from the presence of large amounts of the drug in the solution bathing the inner surface of the membranes.

Pacemaker shift in the sino-atrial node during vagal stimulation.

Abstract: The action of the vagal nerves on the transmembrane potentials of fibres in the S-A node was studied in the isolated right atrium of rabbit hearts. During vagal stimulation the transmembrane potential shows several changes:

The ionic requirements for the production of action potentials in helix pomatia neurones

Abstract: 1. The effect of polarizing currents, ions and drugs on the action potentials of individual neurones in the sub-oesophageal ganglion of the snail Helix pomatia has been examined. 2. The current-voltage relation showed a marked decrease of resistance for the outward current (delayed rectification). AtI=0, the average membrane resistance was 8.3 kΩ×cm2. 3. Tetrodotoxin in a concentration of 4.6×10−6 g/ml did not affect the overshoot or the maximum rate of rise. 0.4% cocaine inhibited delayed rectification, but did not abolish the action potential. 4. Ringer solution with twice the normal Na concentration augmented the overshoot by 5–6 mV and increased the maximum rate of rise to 130% of its normal value. Na-free Ringer decreased the overshoot by only 5–8 mV and reduced the maximum rate of rise to about half its normal value. 5. Even after prolonged perfusion with Na-free solution action potentials were still obtained. The overshoot stayed constant during a 2 hours perfusion period whereas the maximum rate of rise declined slowly. Na-free Ringer with Mn depressed the spike. 6. Raising the Ca concentration of the Na-free Ringer increased the overshoot (average 15.9 mV for a 10-fold increase of [Ca]0), shifted the threshold potential towards zero and slightly augmented the maximum rate of rise. 7. Nominally Ca-free solution markedly reduced the action potential. Excitability was maintained in Na- and Ca-free Ringer with 10 mM Sr or Ba. 8. Part of the results could be explained by assuming a reservoir of Na+ ions in or close to the cell membrane. An alternative explanation is that Ca++ ions participate in carrying charge across the membrane during the rising phase of the action potential. The second hypothesis appears more likely although a definite decision could not be reached.

Increased activity of enzymes of the tricarboxylic acid cycle in response to aldosterone in the toad bladder

Abstract: 1. The activities of condensing enzyme, isocitrate dehydrogenase, glutamate dehydrogenase, glutamate-oxaloacetate transaminase, and malate dehydrogenase increase in toad bladder mucosa in vitro 2 hours after addition of d-aldosterone (10−7 M) to the serosal bathing medium whereas no change in activity of lactate dehydrogenase, aldolase and pyruvate kinase was noted.

Relationship between O2 consumption, high energy phosphates and the kinetics of the O2 debt in exercise.

Abstract: The oxygen consumption together with lactic acid production and concentration of ATP, ADP, and creatinephosphate was measured during exercise and recovery on an isolated dog gastrocnemius Oxygen debt contraction and payment follow an exponential path with a half reaction time of about 20 sec The concentration of ATP and ADP at steady state seem to be unaffected by the intensity of the exercise when this is submaximal and no appreciable production of lactic acid takes place The concentration of creatinephosphate in muscle at steady state decreases with the intensity of the exercise The ratio of the oxygen consumption at steady state to the alactic oxygen debt is identified with the speed constant of the resynthesis of phosphagen in muscle; the half reaction time of this process is 17–20 sec The total alactic oxygen debt amounts to about 50 ml/kg of muscle These figures are in good agreement with earlier data found in man

A Physiological Scheme and Mathematical Model of Temperature Regulation in Man

Abstract: Mean skin temperatures, rectal temperatures and sweat rates were measured on four highly acclimatised subjects. They were exposed for 180 min to 16 different combinations of 4 metabolic rates and 4 air temperatures, ranging from cold (10°C) to hot (49°C). Mean sweat rates for the second hour were plotted against mean rectal temperaturesfor 4 different levels of skin temperature and viceversa. These graphs indicate, firstly, that sweat rate does not increase until rectal temperature rises above a threshold value of 36.5°C; thereafter the increase in sweat rate depends upon the level of mean skin temperature, being greater the higher the mean skin temperature is. Secondly, sweat rate does not increase markedly until mean skin temperature rises above 33°C but the increase in sweat rate above 33°C depends upon the level of rectal temperature, being greater the higher the rectal temperature is. The interrelated effects upon sweat rate of mean skin temperature and core temperature can be explained by means of a relatively simple physiological system, comprising temperature sensors in the hypothalamus and skin, and a heat loss and a heat conservation integrating centre. Mathematical equations have been developed to express the relationships between sweat rate, core, and mean skin temperature for cool conditions, but these relationships are so complex that it is preferable to use an analogue computer for these purposes.

a membrane current related to the plateau of the action potential of purkinje fibers

Abstract: The membrane potential of cardiac Purkinje fibers was changed by a voltage clamp technique and the membrane current was measured. It was shown that a depolarizing step triggers the flow of a component of membrane current which rises within 20 ms to a maximum and declines thereafter within 50 ms. This component of membrane current is positive at membrane potentials positive to −30 mV, it is negative at potentials negative to −30 mV. Following a depolarizing pulse 700–1000 ms have to pass before a second depolarizing step elicits the full amplitude of the current component. Substitution of extracellular chloride by propionate reduces the amplitude of the current component, substitution by nitrate has the opposite effect. Sodium removal from the extracellular solution decreases the current component between resting potential and −30 mV whereas a Ca-free solution has depressant effects in the whole potential range. Changes of the extracellular ionic concentration did not change the membrane potential at which the current changes from positive to negative. Tentative explanations of the nature of this component are given in the discussion.

Microperfusion study of single short loops of Henle in rat kidney.

Abstract: A perfusion study of the loop of Henle of superficial cortical nephrons of rat kidneys was undertaken to evaluate fractional and absolute reabsorption rates of sodium, potassium, and water as a function of perfusion rate. In 56% of control perfusions, net sodium and potassium reabsorption increased in proportion to the increase in perfusion rate. In this group of experiments early distal tubular sodium concentration remained constant or decreased at elevated perfusion rates. while fractional water reabsorption decreased significantly. Essentially similar results were obtained during mannitol and saline diuresis and in dehydrated rats. From measurements of the pressure drop along the loops it was estimated that resistance to flow decreased and tubular diameter of the resistance segment increased when perfusion rate was augmented. In 44% of the experiments early distal tubular sodium concentration increased with elevations of the perfusion rate. In this group net reabsorption of sodium, water, and potassium proceeded at a lower absolute level irrespective of perfusion rate and fractional reabsorption of sodium and potassium decreased with increasing perfusion rates. This behavior is thought not to be representative of the normal function of the loop of Henle.

Transmural gradients of glycolytic enzyme activities in left ventricular myocardium. II. Prolonged hemmorrhagic hypotension.

Abstract: Twelve experiments were performed on healthy, anesthetized dogs on constant ventilation. Blood pressure, acid-base status, oxygen supply and lactate/pyruvate metabolism were monitored in the blood. The activities of nine glycolytic enzymes were assayed in left ventricular myocardium. A presumably irreversible state of hemorrhagic shock was produced by the reservoir technique and its metabolic sequels recorded in the blood. The analysis of coronary sinus blood did not reveal an oxygen deficit of the heart. The majority of the enzymes assayed showed higher activities following shock. Exceptions were pyruvate kinase, LDH and α-HB-DH. Activity differences between sampling sites appeared following shock especially in the inner layer of the left ventricle. The pattern of transmural activity gradients previously found in the normal state was disturbed. The findings are against an oxygen deficit as a cause of cardiac deterioration in shock, suggesting structural derangements possibly due to catecholamine effects or toxic substances of peripheral origin.

Glucose reabsorption in the rat kidney. Microperfusion studies.

Abstract: Mit Hilfe der Mikroperfusionstechnik wurde die Glucoseresorption an einzelnen proximalen Tubuli der Rattenniere in situ bei verschiedenen tubularen Perfusionsstromstarken untersucht 1 Bei normalen Glucosekonzentrationen im Plasma gibt es keine nennenswerte Ruckdiffusion von Glucose aus dem peritubularen Raum in die Tubulusflussigkeit, so das bei der Bestimmung der Glucoseresorptionsrate dieser Faktor zu vernachlassigen ist 2 Eine Anderung der Stromstarke in den perfundierten proximalen Tubulussegmenten fuhrt zu einer gleichsinnigen Anderung der Glucoseresorptionsrate 3 Es besteht dabei eine lineare Korrelation der Glucoseresorptionsrate zur Nettoresorption von Wasser

Reabsorption of inorganic phosphate in the rat kidney

Abstract: Clearance methods were employed to study reabsorption of inorganic phosphate in the rat kidney. Plasma inorganic phosphate concentration was raised stepwise by phosphate infusions. Reabsorption of inorganic phosphate increased and finally reached a maximal value (TmPO 4), which, however, decreased during further phosphate infusions to about 60%. This decline of TmPO 4 during phosphate infusions could be identified as the result of the phosphate loadper se rather than of the volume load. No evidence was obtained for net secretion of inorganic phosphate. In experiments at endogenous phosphate levels, fractional reabsorption of inorganic phosphate was decreased by expansion of extracellular fluid volume from 86% in the control to 75% (P<0.001). A positive correlation was found between fractional reabsorption of water and fractional reabsorption of inorganic phosphate, which suggests a common link between sodium and inorganic phosphate reabsorption at different degrees of extracellular fluid volume expansion.

Selective activation of C-fibers

Abstract: A polarizing current applied transiently to a nerve selectively blocks conduction in the A-fibers, whereas the C-fibers remain unaffected The block is reversible Stimulation of A-fibers by the polarizing current is prevented by appropriately adjusting its slope of rise

Balance between tubular flow rate and net fluid reabsorption in the proximal convolution of the rat kidney. II. Reabsorptive characteristics during constriction of the renal artery.

Abstract: In the present study it is demonstrated that reabsorptive functions of the proximal tubule during partial renal artery clamping display significant differences when compared to spontaneous GFR variations. During moderate clamping fractional fluid reabsorption was 69.8% and fell during severe clamping to 55.2%. Proximal tubular passage time increased progressively with the degree of clamping. This indicates that radius does not change as a function of GFR, a finding supported by microphotography of the renal surface. During moderate arterial clamping proximal reabsorptive rate was correlated to the tubular cross-sectional area, but in the face of severe clamping this relationship was abolished. We conclude, therefore, that mechanisms other than tubular geometry participate in regulating proximal tubular reabsorption, when GFR is altered by arterial constriction.

Respiratory variations of baroreceptor reflex transmission and their effects on sympathetic activity and vasomotor tone

Abstract: Testreizung beider Sinusnerven am narkotisierten Hund mit rein depressorisch wirksamen Reizparametern ergibt verschiedene Reizerfolge, abhangig vom Zeitpunkt der Reizung in bezug auf die Atemphase.

[Behavior of CO2-pressure and bicarbonate in the countercurrent system of renal medulla].

Abstract: Behaviour o/COs-Pressure and Bicarbonate in the Countercurrent System o/ Renal Medulla Summary. On rats anesthetized by Inac t in i.p. a crossincision was made at the upper pole of the ureter so t h a t a small area of the kidney medulla was accessible to micropnncture studies. Samples taken from vasa recta, collecting duct and from arteria renalis were sucked in a microglasselectrode for measuring the actual pH. The construction of this pH-electrode (suction type) is described in details, pH values after equilibration of each sample with three known C02-pressures yielded a calibrating line for calculating the Pco~ from the measured actual pH value. The bicarbonate concentrat ion of the samples was calculated by using the Henderson-Hasselbalch equation. Experiments were done on infusion to the animal with following various solutions: 1. containing isotonic bicarbonate only; 2. bicarbonate and Diamox; 3. bicarbonate and carbonic anhydrase (CA); 4. isotonic NaC1 solution used as control. In the control animals there was no difference of blcarbonate-concentratiou in vasa recta and arteria renalis samples. I t suggests, t ha t bicarbonate is not involved in the concentrat ing process of the medulla. The bicarbonate concentrat ion in vasa recta did not arise before the bicarbonate concentration in collecting ducts reached high values. During bicarbonate infusion the C02-pressure in vasa recta blood was the same as in control bu t about 10 mm Hg above t ha t of arteria renalis samples. Inhibi t ion of carbonic anhydrase with Diamox enlarged the C02-pressure difference between arteria renalis and vas rec tum up to 40 mm ttg. So it is concluded t h a t the increase of Pco2 in the kidney medulla is mainly due to delayed dehydrat ion of carbonic acid. However, the CO2-pressure in collecting duct samples in bo th conditions was significantly higher t han t h a t in vasa recta. The C02-pressure difference indicated delayed dehydration, since the samples from collecting duct contained no CA and the carbonic acid came to equilibrium with CO~-pressure after the collection. When in contras t to these experiments the animal was infused with carbonic anhydrase, there was no delayed dehydrat ion in all nephron sections. Therefore the Peo, in collecting duct and vasa recta samples became equal.

The effect of potassium on the tone of isolated arteries

Abstract: Segments of bovine facial arteries were placed under a pressure of 100 mm Hg and the inside pressure was isometrically recorded. The arteries were rinsed from outside with various potassium solutions.

Sodium and water reabsorption in different parts of the nephron in rats with experimental hypertension

Abstract: 4 Wochen nach Klammerung einer Nierenarterie war der Perfusionsdruck der geklammerten Niere normal, wahrend der arterielle Mitteldruck auf 188 mm Hg angestiegen war. Die Ausscheidung von Natrium und Wasser im Harn der geklammerten Niere war normal, im Harn der ungeklammerten Niere erheblich hoher als normal. Glomerulumfiltrat (pro g Niere), intratubularer Druck, Tubulusweite, Passagezeit von Lissamingrun und die fraktionelle Resorption von Natrium und Wasser waren im proximalen Tubulus sowohl in der geklammerten wie in der ungeklammerten Niere normal. In der ungeklammerten Niere war die Passagezeit durch die Henlesche Schleife stark verkurzt und die Resorption von Natrium und Wasser in der Schleife erheblich vermindert. Diese Veranderungen — obwohl zum Teil kompensiert durch vermehrte Resorption im distalen Tubulus und im Sammelrohr — sind verantwortlich fur die hohere Wasser- und Natriumausscheidung der ungeklammerten Niere. Die Ursache ist wahrscheinlich eine starkere Durchblutung des Nierenmarkes. Im Nephron der geklammerten Niere war die fraktionelle Natrium- und Wasserresorption nicht signifikant von normalen Werten verschieden mit der Ausnahme einer niedrigeren Natriumresorption im distalen Tubulus und einer hoheren Natriumresorption im Sammelrohr. Der Natrium-Transport im distalen Tubulus ist anscheinend gestort; TF/P−Na+ betrug im Mittel 0,6 bis zum Ende des distalen Tubulus. Die Ergebnisse konnen die unterschiedliche Harnausscheidung erklaren, die beim Hypertoniker mit einseitiger Nierenarterienstenose beobachtet wird (Howard-Test).

Analyse des Frequenzganges druckinduzierter Änderungen des Strömungswiderstandes isolierter Rattennieren

Abstract: Fur das Praparat der isolierten Rattenniere wurde die Abhangigkeit der Amplitude des Volumenstromes und die des Phasenwinkels (zwischen Perfusionsdruck und Volumenstrom) von der Frequenz der Druckanderungen (d.i. der Amplituden- und der Phasenfrequenzgang) mit Hilfe eines Digitalprogrammes aus Volumenstromkurven nach rechteckigen Drucksprungen errechnet. Die so gewonnenen Amplitudenfrequenz- und Phasenfrequenzgange stimmen mit fruher direkt gemessenen uberein (Basar u. Mitarb., 1968). Die Frequenzauflosung und die Amplitude der charakteristischen Maxima sind jedoch erhoht. Der Frequenzbereich sowohl zu niedrigeren als auch zu hoheren Frequenzen hin ist erweitert. Bei Frequenzen zwischen 0,4 und 4 Hz ergibt sich ein Nacheilen des Phasenwinkels, wahrend bei tieferen Frequenzen der Volumenstrom dem Druck vorauseilt, also eine Uberschusreaktion auf den Druckreiz eintritt. Nach Diskussion und Vergleich der Abhangigkeit der Spannungsentwicklung anderer glatter Muskulatur von der Frequenz aufgezwungener Dehnungen werden die Ergebnisse als Hinweis auf einen direkt-myogenen Mechanismus der Autoregulation des Volumenstromes der Niere interpretiert.

Amiloride and the mode of action of aldosterone on sodium transport across toad bladder and skin

Abstract: The characteristics of the inhibitory influence exerted by amiloride on active sodium transport by toad bladder and skin were taken advantage of to shed additional light on the mechanism whereby hormones-chiefly aldosterone-stimulate sodium transport across such epithelia.

The effect of stimulus area on the response of movement detecting neurons in the frog's retina

Abstract: 1. The action potentials of single optic nerve afferent endings in the superficial layer of the tectum opticum of the frog were recorded by means of metalfilled micropipets. The responses of class 2 and class 3 neurons to round or rectangular black stimuli moved on a white background through the receptive field were quantitatively analyzed. The area of the black stimuli was the parameter examined in this series of experiments. 2. A logarithmic relationship between the stimulus area and the neuronal response, measured as impulse frequency during the traverse of the stimulus through the excitatory receptive field (ERF) was found to be valid (eq. 1). 3. If stimuli larger than the ERF were used, the neuronal activation decreased because of the excitation of the inhibitory receptive field surrounding the ERF. For this decrease a logarithmic dependence on the stimulus area was again found to be valid. 4. The findings can be explained by a model of the receptive field in which an inhibitory Gaussian distribution is superposed on an excitatory Gaussian distribution of narrower width and in which the inhibition is of the multiplicative type. 5. The data obtained in neurophysiological experiments are compared with findings of studies on the catching behavior of frogs.

Micropuncture studies on the dog kidney. I. The response of the proximal tubule to changes in systemic blood pressure within and below the autoregulatory range.

Abstract: Micropuncture studies were carried out on the dog kidney in order to delineate the response of micropuncture parameters to changes in blood pressure within and below the autoregulatory range. By the use of chloralose anaesthesia and carotid sinus denervation elevations in systemic blood pressure were induced, while the use of Regitine permitted the induction of lower BP levels both in the lower part of the autoregulatory range and to frankly hypotensive levels. The results indicate a constancy of intratubular function (TF/P inulin, transit time, single nephron GFR, intratubular pressure) so long as blood pressure remained within the autoregulatory range, supporting the concept of a preglomerular site for autoregulation. During hypotension the single nephron GFR decreased, the transit time was prolonged, but the end proximalTF/P inulin did not change significantly. These changes in tubular function corresponded to a fall in total GFR, RBF, and filtration fraction. The fall in single nephron GFR was greater than the corresponding fall in total GFR suggesting that during hypotension the filtrate of the punctured superficial nephrons is less well protected than that of other nephrons in the dog kidney.

The diffusion coefficient of myoglobin in muscle homogenate.

Abstract: One layer of muscle homogenate rich in myoglobin (heart muscle of the rat) and three layers of muscle homogenate poor in myoglobin (skeletal muscle of the rat) were arranged one upon the other, than reseparated after a certain time. According to the concentration change of myoglobin in the layers the diffusion coefficient of myoglobin is 1.5×10−7 cm2/sec at 20° C and 2.7×10−7 cm2/sec at 37° C. From this result it was calculated that the facilitated O2 diffusion on the basis of myoglobin diffusion amounts, at 37° C, to the free O2 diffusion at about 3 mm Hg partial pressure difference when myoglobin concentration is 2×10−7 mol (3 mg) per g wet muscle.