bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of naive and experienced students of elementary physiology on performance in an advanced course.
Authors: Richardson D R
Published: December 2017

The purpose of this study was to determine whether, in comparison with naive students, experienced students who have completed an elementary physiology course 1) have a greater knowledge level of physiology and 2) perform better in an upper division physiology course. The educational setting for this study was the cardiovascular block of an advanced undergraduate level course entitled Principles of Human Physiology (PGY 412). The study employed students who had completed elementary physiology (PGY 206) at the University of Kentucky (group 1), students who had completed elementary physiology in another academic program (group 2), and naive students with no prior physiology experience (group 3). A cardiovascular pretest was presented during the opening session of the cardiovascular block in PGY 412. Respective scores for the three groups were 29.4%, 31.7%, and 24.1%, and there were no significant between-group differences. Respective scores on the same pretest items given as a posttest at the end of the cardiovascular block were 90.4%, 91.4%, and 90.4%, and, again, there were no significant between-group differences. Respective scores on other cardiovascular test items given at the end of the block were 78.9%, 78.7%, and 81.1%. Interestingly, the highest score here was achieved by the naive students (group 3), but, once again, between-group differences were not significant. In summary, on the basis of pretest/posttest examination of cardiovascular physiology between naive and experienced students, the results of this study indicate 1) that the common assumption that students entering advanced level physiology courses have a significant retention of knowledge from elementary physiology is not valid and 2) that completion of an elementary physiology course does not offer an advantage in learning advanced material.
Combination of didactic lecture with problem-based learning sessions in physiology teaching in a developing medical college in Nepal.
Authors: Ghosh S , Dawka V
Published: December 2017

Physiology teaching as an essential part of medical education faces tremendous criticism regarding curriculum design, methods of implementation, and application of knowledge in clinical practice. In the traditional method of medical education, physiology is taught in the first year and involves little interdisciplinary interaction. The Manipal College of Medical Sciences, Pokhara, Nepal (affiliated with the Kathmandu Univ.) started in 1994 and adopted an integrated curriculum drawn along the lines of the student-centered, problem-based, integrated, community-based, elective-oriented, and systematic (SPICES) medical curriculum. Here, physiology is taught for the first 2 yr of the 4.5-yr Bachelor of Medicine, Bachelor of Surgery course. Methodology adopted is as follows. For a particular topic, objectives are clearly defined and priority content areas are identified. An overview is given in a didactic lecture class to the entire batch of 100 students. Tutorial classes are conducted thereafter with smaller groups of students (25/batch) divided further into five subgroups of five students each. In these sessions, a problem is presented to the students as a focus for learning or as an example of what has just been taught. Each problem was accompanied with relevant questions to streamline the students' thought processes. A tutor is present throughout the session not as an instructor but as a facilitator of the learning process. A questionnaire sought students' opinion on the usefulness of this approach, relevance of the combination of problem-based learning (PBL) sessions and didactic lectures in understanding a particular topic and relating clinical conditions to basic mechanisms, and improvement of performance on the university final examination. The majority of the students opined that the combination of didactic lectures and PBL sessions was definitely beneficial regarding all the above-mentioned aspects of learning. The university results corroborated their opinion. Thus it may be considered that a judicious mixture of didactic lectures and PBL sessions is beneficial as a teaching module of physiology in medical schools.
Differentiation between endogenous pyrogen and leukocytic endogenous mediator
Authors: Mapes C. A. , Sobocinski P. Z.
Published: December 2017

The crude material released from glycogen-stimulated rabbit peritoneal polymorphonuclear leukocytes when administered to experimental animals elicits a number of metabolic and physiologic alterations characteristic of those observed in the host inflammatory response. Classically, the mediator of febrile response observed in rabbits and other species has been termed endogenous pyrogen (EP), whereas leukocytic endogenous mediator (LEM) has been used as a general term to denote the substance(s) mediating multiple inflammatory responses observed in rats. The latter substance, however, has not been previously demonstrated to differ from EP. This report presents evidence indicating that EP and LEM are different molecular species. Evidence supporting the differentiation between these entities includes: physical separation of EP from one or more mediators that induce metabolic alterations attributed to LEM; production of LEM activities by stimulated polymorphonuclear leukocytes in the absence of detectable pyrogenic activity; and differences in the release of EP and LEM from stimulated rabbit granulocytes in the presence of potassium ion.
How Gymnodinium breve red tide toxin(s) produces repetitive firing in squid axons
Authors: Westerfield M. , Moore J. W. , Kim Y. S. , Padilla G. M.
Published: December 2017

Partially purified toxin(s), GbTX, extracted from Gymnodinium breve red tide organisms elicits a spontaneous train of action potentials in the squid giant axon. The spikes have a shape similar to that in the normal seawater control except for an increase in the rate of recovery from the afterhyperpolarization. With this more rapid recovery, the membrane potential overshoots the resting potential and threshold, triggers another spike, and thus produces repetitive firing. Voltage-clamp studies revealed that the toxin has no effect on the normal sodium or potassium conductance changes produced by step depolarization. However, consistent with the faster recovery after an action potential, GbTX speeds recovery of the “shut-off” currents to their steady-state values after a depolarization. The most likely mechanism by which the toxin accelerates recovery after an action potential (leading to repetitive firing) is the induction of a small additional inward current which was found to be reduced by prehyperpolarization. This toxin-induced current which speeds recovery is blocked by tetrodotoxin and hence presumably flows through the sodium channel.
Effect of inhibitors on transepithelial efflux of Na and nonelectrolytes in frog skin
Authors: Biber T. U. , Mullen T. L.
Published: December 2017

The transepithelial efflux of Na and several nonelectrolytes (mannitol, sucrose, and polyethylene glycol 900) were measured in the isolated frog skin under short-circuited conditions in chambers that had been specially designed to avoid edge damage. Ouabain (10(-3) and 10(-4) M) caused a dramatic increase in the efflux of Na, whereas the efflux of nonelectrolytes showed only a slight alteration. The efflux of Na increased after the application of dinitrophenol (10(-4) M), whereas the efflux of nonelectrolytes remained constant. Amiloride (10(-3) M) caused large variations in the efflux of Na, whereas the efflux of nonelectrolytes remained unchanged. The results provide evidence that these inhibitors do not alter the permeability of the paracellular pathway and that the total transepithelial efflux of Na or at least a very large portion of it, and possibly also the transepithelial efflux of Cl, proceeds via a transcellular pathway and not a paracellular pathway as has been widely accepted. The data further suggest that the Na proceeding via this pathway interacts directly or indirectly with the active transport step.
A bone matrix calcification-initiator noncollagenous protein
Authors: Urist M. R. , Mikulski A. J. , Nakagawa M. , Yen K.
Published: December 2017

When completely demineralized, the densely packed structure of bone matrix does not recalcify, neither in physiologic solutions in vitro nor in implants in vivo. Even when inorganic and organic calcification inhibitors (which normally are stored in bone matrix) are removed first by autolytic digestion in neutral buffers at 37C and then by sequential chemical extraction, implants of the EDTA insoluble residue will not recalcify after as long as 4 wk in a muscle pouch. However, if first demineralized in cold dilute HCl, second, extracted and autodigested in buffers solution at 37C, and then further extracted in EDTA and other solutions at 2C, a calcification initiator protein (Cp) is unmasked, and the residue will invariable recalcify. CIP, isolated by gel filtration and column chromatography, is a disulfide-bonded glycoprotein aggregate composed of subunites of a moleclar mass of 55,000. CIP is composed of a large proportion of acidic amino acids and has a calcium binding capacity of about 1.8 times greater than albumin. The affinity constant CaCIP, calculated by ultrafiltration of physiologic solutions of Ca2+, is log K, 2.9. Observations on implants of residues that containe a) CIP but not a bone morphogenetic property (BMP), B) BMP accompanied by CIP activity, or c) neither BMP nor CIP activity suggested that BMP covers CIP and that the two are attached to bone collagen in tandem. Whether CIP plays a part in calcification of the normal skeleton requires further investigation.
Effects of cadmium and lead on adrenergic neuromuscular transmission in the rabbit
Authors: Cooper G. P. , Steinberg D.
Published: December 2017

The effects of inorganic lead (PbCl2) and cadmium (DdCl2) on the pressor response of rabbit saphenous arteries produced by sympathetic nerve stimulation were examined. A 1- to 3-cm length of artery was removed, placed in a bath containing mammalian Ringer solution, and perfused with the same solution at a constant rate sufficient to maintain a 40-60 mmHg perfusion pressure. Increases in perfusion pressure resulting from electrical stimulation -f periarterial nerve endings were reduced or completely blocked by the addition of 5-20 muM lead or cadmium to the bathing solution for a period of 15-30 min. Responses to norepinephrine or to direct electrical stimulation of the muscle remained relatively unaffected. During lead or cadmium blockade, the response to nerve stimulation could be restored by a fourfold increase in calcium concentration. It is concluded that lead and cadmium reduce the response to sympathetic nerve stimulation primarily through an effect on presynaptic nerve terminals.
Effect of hyperosmolarity on resting and developed tension in heart muscle
Authors: Vargas F. F. , Johnson J. A.
Published: December 2017

Simultaneous changes in weight, tension, and electrical activity were studied in the isolated perfused rabbit heart when the Ringer solution perfusion fluid was made hypertonic by the addition of sucrose, urea, glycerol, ethylene glycol, or formamide. The typical responses to each of the molecules was an initial drop in weight and tension followed by a return toward the base-line level. A 0.4 M concentration of sucrose, urea, or glycerol reduced the weight to 40 +/- 4.6, 48 +/- 3, and 52.2 +/- 3% of the initial value, respectively. The tension was simultaneously reduced to 23 +/- 3.5, 31 +/- 2, and 41 +/- 4% of its initial value. The tension drop produced by the solutes tested was linearly related to the amount of water lost by the heart. The falling phases of both tension and weight loss were closely correlated phases of both tension and weight loss were closely correlated in time a magnitude and were both related to the effectiveness of a particular molecule to move water out of the cells. In contrast, the subsequent rising phases of tension and weight were not as well correlated in time and magnitude. Whereas for most of the molecules used, the tension recovery was incomplete; urea, in contrast, caused an overshoot of the control tension level, thus pointing toward a unique inotropic effect of this compound. Resting tension rose for both urea and sucrose but not for the other compounds.
Amine uptake and metabolism by endothelium of pig pulmonary artery and aorta
Authors: Junod A. F. , Ody C.
Published: December 2017

The uptake and metabolism of 5-hydroxytryptamine (5HT) and l-norepinephrine (NE) were measured in endothelial cells of pig pulmonary artery and aorta, as well as in lung slices. Evidence for oxidative deamination and for a saturable uptake mechanism, sensitive to cold, imipramine, and NA+-free medium was obtained for 5HT in lung slices and in the pulmonary as well as in the aortic endothelium, separated from the lumen by absorption to Millipore filters or by exposure to collagenase. For NE, however, a similar type of uptake could be deomonstrated in lung slices only. In the aortic and pulmonary endothelium, NE was metabolized, but its uptake was not influenced by imipramine, Na+-free medium, and high substrate concentration. The aortic and pulmonary endothelium have, therefore, similar properties and exhibit for 5HT, but not for NE, a type of uptake similar to that existing in lung capillaries.
Differentiation between endogenous pyrogen and leukocytic endogenous mediator
Authors: Mapes Carol A. , Sobocinski Philip Z.
Published: December 2017

Page C15 “Mapes, Carol A., and Philip Z. Sobocinski. Differentiation between endogenous pyrogen and leukocytic endogenous mediator. Am. J. Physiol. 232(1): C15–C22, 1977 or Am. J. Physiol.: Cell Physiol. 1(1): C15–C22, 1977.”
Fatigue and posttetanic potentiation in single muscle fibers of the frog
Authors: Vergara J. L. , Rapoprot S. I. , Nassar-Gentina V.
Published: December 2017

At 15 degrees C, direct stimulation of frog single muscle fibers at a frequency of 20 Hz produced a tetanic tension that remained constant for 20 s and then declined. The decline was reversed during 1-s interruptions of the stimulus train in the first 50 s of stimulation, but not with longer stimulation. Posttetanic potentiation (PTP), characterized by prolonged twitch relaxation and contraction times and elevation of twitch height, remained for 10-40 min after a 10-s tetanus and for at least 90 min after a 50- to 150-s tetanus. Posttetanic fatigue appeared only after at least 50s of tetanic stimulation. Fatigue was manifested invariably by a reduction in the height of a 200-ms tetanic contraction and usually by a reduction in twitch height after PTP. Fatigued fibers recovered normal contractile responses in 40–160 min. Hypertonic solutions, which blocked contraction in response to tetanic stimulation, prevented posttetanic fatigue but not PTP. The observations suggest that fatigue is caused by a failure in excitation-contraction coupling, probably in relation to consumption of metabolic substrates. Even 10-s tetani which do not produce fatigue can affect muscle contractile function for up to 40 min.
Characteristics of thyroid-stimulated Na+-K+-ATPase of rat heart
Authors: Philipson K. D. , Edelman I. S.
Published: December 2017

The possibility that augmentation of cardiac Na+-K+-dependent adenosine triphosphatase (Na-K-ATPase) by L-3,5,3'-triiodothyronine (T3) was mediated by early changes in intracellular ion concentrations ([Na+]1, [K+]1) was explored by time-course analysis after a single injection of T3 in thyroid-ablated (131I) rats. At 6 and 16 h after injection, T3 had no significant effect on cardiac [Na+]1, [K+]1, or microsomal Na-K-ATPase activity. At 24 and 48 h, however, T3 elicited proportionate increases in [K+]1 and Na-K-ATPase activity. Thus, no evidence was adduced that the T3-dependent increase in ventricular Na-K-ATPase activity is an adaptive response to prior changes in intracellular ion concentrations. The increase in [K+]1 is attributable to an increase in Na+ pump activity. Administration of T3 to hypothyroid rats had no effect on the transition temperature or the activation energy of ventricular microsomal Na-K-ATPase, as analyzed by an Arrhenius plot. Thus, the lipid microenvironment and the properties of the enzyme may be independent of thyroid status. The latter inference was supported by kinetic analysis, in that T3 had no effect on the Km for ATP or the K1/2's for Na+ and K+. Injection of T3 of the hypothyroid rat, however, significantly increased the Vmax's for ATP, Na+, and K+ of ventricular microsomal Na-K-ATPase. These results are in accord with the inference of thyroidal induction of Na-K-ATPase indistinguishable from those present in the athyroid state.
Modifications of glass microelectrodes: a self-filling and a semifloating glass microelectrode
Authors: Sato K.
Published: December 2017

A simple and inexpensive method for constructing a double capillary was developed for preparing a self-filling glass microelectrode. The modified method uses a thin capillary instead of a bundle of glass fibers and fuses it to the outer capillary wall with flame before pulling the latter with a puller. The validity of the new electrode was proven by measuring the proximal cell PD of the rat kidney slices (mean of the stable cell PDs lasting longer than 30 min,‥69 mV). A semifloating electrode was modified from the original floating electrode to be applicable to the in vivo kidney preparation whose pulsatile and respiratory movements had hindered yielding a stable cell PD. This electrode is constructed simply by replacing the shaft of the Ling-Gerard glass microelectrode with a length of flexible silcone-rubber tubing. The cell PD recorded by this electrode is found to be more stable and can withstand minor tissue distortion in mammalian kidney cells in vivo and also in such a contractile tissue as the secretory coil of the eccrine sweat gland.
Rate of heat production related to degree of filament overlap in chick ALD muscle
Authors: Matsumoto Y. , McPhedran A. M.
Published: December 2017

The anterior latissimus dorsi (ALD) of chicks (2 wk old) was examined for rate of heat liberation when the muscle was reversibly stretched from L0 to about 1.6 L0. The "plateau" forces of isometric tetani were related to the corresponding rates of heat liberation. Presumably, in this region of length change the degree of overlap between the thick and thin filaments is changing. If the amount of overlap is known, the number of heavy meromyosin cross bridges in activity can be estimated. From this information, the amount of liberated energy can be calculated for a single cross-bridge cycling. In all of our measurements, there was heat production even at muscle lengths so great that no filament overlap would have to be assumed. This finding was incorported into the estimate for energy release per cross-bridge cycling.
Transfer of hydrophilic molecules by placenta and yolk sac of the guinea pig
Authors: Thornburg K. L. , Faber J. J.
Published: December 2017

Prenatal transfer of hydrophilic materials was studied in chronic guinea pig preparations of ca. 30-65 days gestation. In most preparations the vitelline (yolk sac placenta) circulation of one of the fetuses was ligated between 1 and 20 days before the experiment. Fetal and maternal serum protein concentrations were recorded as a function of the number of days after ligation. Prenatal transfer of hydrophilic materials of 60-5,500 daltons molecular wt was consistent with diffusion, with some evidence of steric restriction of the larger molecules. There was no difference between operated and sham-operated or control fetuses. However, the transfer of radiolabeled homologous gamma globulin ceased after ligation of the yolk sac vessels. The transfer in control fetuses accounted for most of the prenatal requirements of this protein, as calculated from the increases in fetal weight and serum gamma globulin concentrations as a function of gestational age. There was evidence of a nonspecific suppression of yolk sac function by surgery but no evidence of fetal catabolism of gamma globulin.
Effect of oxygen tension on cellular energetics
Authors: Wilson D. F. , Erecinska M. , Drown C. , Silver I. A.
Published: December 2017

Simultaneous measurements of the mitochondrial [NAD+]/[NADH], the cytoplasmic [ATP]/[ADP] x [Pi], and the respiratory rate were carried out in suspensions of cultured kidney cells in a range of defined oxygen tensions. The results show that as the extracellular oxygen concentration falls there is a decrease in the respiratory rate, which is accompanied by a decrease in the [ATP]/[ADP] and a progressive reduction of cytochrome c. Even at low O2 tensions the mitochondrial respiratory chain between the NAD couple and cytochrome c remains at near equilibrium with the ATP synthesizing reactions. It is concluded that limited oxygen supply affects cellular metabolism at much higher concentrations than the P50 value for the oxygen dependence of respiration, but the respiratory rate remains relatively unchanged due to compensatory changes in the [ATP]/[ADP] X [Pi] and progressive reduction of cytochrome c. These metabolic changes may form a basis for the phenomenon of tissue oxygen sensing at near physiological oxygen tensions.
Metal-film thermopiles for use with rabbit right ventricular papillary muscles
Authors: Mulieri L. A. , Luhr G. , Trefry J. , Alpert N. R.
Published: December 2017

A method of fabricating Hill-Downing type, planar thermopiles by vacuum-deposition techniques is described in detail. The present model was designed for initial heat measurements on rabbit papillary muscles as small as 1 mg blotted wt, but it is also suitable for small bundles of frog muscle fibers (30–75). The thermopile has 20 or 14 junctions, an active length of 5 or 3.5 mm, and an actual thickness of 20 micrometer. It has an effective heat capacity of about 0.3 mcal/degrees C, a heat loss coefficient of about 0.3 mcal/degrees C - s, a temperature sensitivity of 1.4 mV/degrees C (20 junctions), and an electrical resistance of 180–200 omega. Infrared-emitting diodes are used to heat the thermopile and muscle artificially for thermal time constant and conduction-delay measurements. Performance of the thermopiles is demonstrated with initial heat records from rabbit right ventricular papillary muscles and a bundle of frog semitendinosus muscle fibers. Results of preliminary experiments concerning latency for heat generation, initial rate of heat generation, and activation heat in both types of muscles are presented.
Characterization of frog muscle mitochondria
Authors: Skoog C. , Kromer U. , Mitchell R. W. , Hoogstraten J. , Stephens N. L.
Published: December 2017

Studies on oxidative phosphorylation revealed that, in frog skeletal muscle mitochondria (SKMM) from the thigh, the adenosine diphosphate/oxygen ratio (ADP/O) was 2.8 +/- 0.1 SE, and the respiratory control ratio was 9.5 +/- 0.9, with pyruvate/malate as the substrate. Oxygen uptake rate (Qo2) was 225 mumol O2 per minute per gram mitochondrial protein +/- 13; phosphorylation rate (ADP/O X Qo2 X 2) was 1,230 mumol ADP phosphorylation per minute per gram mitochondrial protein +/- 77; and the phosphorylation capacity (phosphorylation rate times tissue mitochondrial protein content) was 3.6 mumol ADP phosphorylated per gram wet weight of muscle +/- 0.2. Tissue mitochondrial protein content was determined by the measurement of nicotinamide adenine dinucleotide (NADH) oxidase activity. Electron microscopy (EM) revealed intact, isolated, energized twisted mitochondria of a condensed form. Frog sartorius muscle mitochondria gave similar oxidative phosphorylation parameters when investigated independently of the rest of the thigh. These values of SKMM respiration from the frog are similar to those values obtained from pigeon and rabbit heart and rat skeletal muscles. However, because of the low NADH-oxidase activity indicating reduced mitochondrial content (this was verified in low-magnification EM pictures), phosphorylation capacity was significantly reduced in frog skeletal muscle mitochondria.
Properties of thyroidectomized rat extensor muscle
Authors: Grossie J.
Published: December 2017

Basic mechanical and electrical properties of rat extensor muscle were analyzed 4--6 wk after thyroid removal. Isometric twitch tensions in thyroidectomized (Tx) rat muscle varied considerably, with over 60% of the muscles showing abnormally low values and the remainder showing a high twitch force. The duration of the twitch was significantly increased from 137 to 245 ms but contraction and half-relaxation times were not significantly changed. Tetanic force was not effected by thyroidectomy. Electrical properties of the muscle fiber membranes were made exclusively via intracellular techniques. The resting membrane potential was slightly higher in thyroidectomized rats (-79 mV) as compared to sham controls (-78 mV). Both direct and indirect action potentials showed higher overshoots, amplitudes, and rates of depolarization in thyroidectomized rats. The threshold of the indirect action potential appeared at a higher transmembrane potential as compared to sham-operated controls. The input resistance, space constant, time constant, and specific membrane resistance were all significantly increased in thyroidectomized rat extensor muscle, whereas fiber diameter and capacitance were significantly decreased. Estimates of specific ionic conductance show that both potassium and chloride conductance are decreased in thyroidectomized rat muscle.
Effect of lanthanum and reduced temperature on 45Ca efflux from rabbit aorta
Authors: Deth R. C.
Published: December 2017

The ability of lanthanum (La3+) to block calcium efflux from smooth muscle cells of the rabbit aorta has been examined. La3+ promotes the very early phase of 45Ca efflux, which is extracellular in origin, and partially inhibits the latter, cellular portion. Stimulation of 45Ca efflux caused by the release of intracellular 45Ca with either 10(-4) M dinitrophenol or 10 mM caffeine was not reduced by pretreatment with 10 mM La for 40 min, whereas stimulation due to norepinephrine was abolished. It was concluded that during the use of the "La method" for measuring cellular 45Ca there is an underestimation due to unblocked 45Ca loss. This loss can be reduced by processing tissue at 2 degrees C, which inhibits transport processes. The time course of 45Ca uptake and the stimulation of uptake by high K+ are qualitatively but not quantitatively similar if tissues are washed at 37 and 2 degrees C. Tissues washed in La3+ at 2 degrees C for 60 min retain approximately double the cellular 45Ca of those washed at 37 degrees C. This methodology provides an improved correlation between estimates of cellular calcium derived from 45Ca uptake and 45Ca efflux experiments.
A bipolar electrode for electromyography of limb muscles of small animals
Authors: Stephenson R. S.
Published: December 2017

A bipolar electrode for recording from or stimulating the skinned surface of small, moving muscles is described. The electrode is so light that it clings to the moist surface of the muscle and moves with it, like a piece of confetti. It can be positioned or repositioned instantly and with no damage to the muscle. Because of its small size and bipolar nature, it records from or stimulates a very small volume. It is inexpensive, simple, and requires no special apparatus for its consturction. The electrode is especially suited for muscles in the limbs of small animals, in which movement and small size present special problems.
Effects of pH, Ca, ADH, and theophylline on kinetics of Na entry in frog skin
Authors: Mandel L. J.
Published: December 2017

The short circuit current as a function of Na concentration in both solutions was found to obey Michaelis-Menten kinetics under a variety of experimental conditions. Values of maximal transport rate (Im) and half-maximal Na concentrations (Kt) were determined from these experiments. Three type of results were obtained: 1) Im and Kt both decreased by approximately the same fraction when the pH of both solutions was reduced by increasing PCO2, 2) Im decreased and Kt increased when the external pH was decreased, and 3) Im increased with ADH and theophylline, decreased with external Ca, and Kt remained unchanged. Various criteria were utilized to determine that these were properties of the entry barrier for Na into the "transport pool." The results are explained in terms of a model that separates three different types of actions on the entry barrier: 1) competition of Na with other ions in the external solution for entry, 2) modulation of the number of sites available for Na translocation by changing the cytoplasmic pH, and 3) alterations in the rate of Na translocation caused by changes in the Na permeability or the electrochemical gradient across the entry barrier.
Contribution of sodium pump to resting potential of squid giant axon
Authors: de Weer P. , Geduldig D.
Published: December 2017

The effect of the cardiotonic aglycone, strophanthidin, on sodium and potassium efflux, membrane potential, membrane conductance, potassium permeability, and the shape of the action potential of the giant axon of the squid, Loligo pealei, was examined. Strophanthidin depolarized the membrane to an extent determined by the intracellular sodium concentration, except in axons pretreated with cyanide, in which the effect is abolished. Cyanide itself hyperpolarized the axon membrane. Axons treated with strophanthidin appear to be better potassium electrodes, but this observation is fully accounted for by the stimulating effect of [K]o on an electrogenic sodium pump. The increase in potassium efflux produced by strophanthidin is also well accounted for by the observed membrane depolarization and the known dependence of potassium permeability on membrane potential (e-fold increase in efflux per 6.4 mV depolarization). Strophanthidin has no demonstrable effect on membrane conductance apart from that due to the observed depolarization. These findings support the view that cardiotonic steroids, at least in nerve, are specific inhibitors of the sodium pump, devoid of effects on permeability that might interfere with the study of electrogenic pumping. The alteration in the shape of the action potential after exposure to strophanthidin (deepening of the "underswing") suggests that the strophanthidin-induced membrane depolarization results from the inhibition of a true electrogenic pump, and not from ion redistributions in the vicinity of the membrane.
Cellular Cl content and concentration of amphibian skeletal and heart muscle
Authors: Macchia D. D. , Polimeni P. I. , Page E.
Published: December 2017

Toads (Bufo marinus) and frogs (Rana pipiens pipiens) were given intraperitoneal injections of Na36Cl and Na235SO4. After in vivo equilibration for 20--180 min, the animals were pithed, and their ventricular and semitendinosus muscles were excised. Measurements of total Cl (by titrimetry) and 36Cl (by radioassay) showed that specific radioactivities of plasma and mus les approached equality within 1 h after injection for toad skeletal and heart muscle and frog ventricles, indicating complete exchange of cellular Cl with 36Cl. From the simultaneously measured muscle water contents and 35SO4 spaces, intracellular Cl concentrations in vivo (in mumol/g cell water) for semitendinosus and ventricular muscles were calculated to be, respectively, 1.4 +/- 0.3 and 2.3 +/- 0.8 for Bufo and 1.7 +/- 0.7 and 4.8 +/- 2.4 for Rana. In view of these low values, active cellular Cl accumulation seems improbable, but cannot be rigorously excluded without simultaneous membrane potential and intracellular ion activity measurements. A high concentration of Cl in the sarcoplasmic reticulum of skeletal muscle is also inconsistent with these measurements.
Calcium and the control of potassium efflux in the sublingual gland
Authors: Putney J. W. , Leslie B. A. , Marier S. H.
Published: December 2017

The effects of cholinergic stimulation on K efflux from rat sublingual gland slices was investigated. The sublingual gland slices appeared stable on incubation as indicated by electrolyte content and ultrastructural analysis. Carbachol induced a biphasic increase in release of 86Rb (an index of K efflux); a transient phase lasting 2--4 min was followed by a sustained (or slowly falling) phase. Both phases of the response were blocked by atropine, but only the sustained phase was blocked by omission of Ca or by the addition of LaCl3. The divalent cationophore A-23187 produced a Ca-dependent release of 86Rb. Substance P stimulated a biphasic release of 86Rb, similar to that obtained with carbachol, but epinephrine did not. The response to substance P demonstrated a Ca dependence similar to that of carbachol. When a transient response to carbachol was elicited, no transient response to carbachol was elicited, no transient response to substance P could be obtained. This suggests that the receptors for these agonists may reside in the same cells. Also, the magnitude of the responses suggests that most of the affected cells are probably the mucous elements of the sublingual gland.
A piezoelectric force transducer for single muscle cells
Authors: Chiu Y. L. , Karwash S. , Ford L. E.
Published: December 2017

A cantilevered piezoelectric force transducer is described. The cantilevered element has a 6-mm glass extension that can be projected into a horizontal muscle bath from above. By adjusting the length of the piezoelectric bar from 1 to 4 mm, the sensitivity of the device can be varied between 25 and 100 mV/mN (0.25--1.0 mV/mg) with its resonant frequency varying inversely between 8 and 15 kHz. Although moderately fragile, the sensing elements are inexpensive and easily made. The output of the sensing element is amplified by a small, unity-gain, high-input-resistance amplifier mounted on a support block with the element. Although the arrangement does not provide a DC output, its time constant of over 500 s is sufficiently long for measuring tension during muscle contractions lasting 1--2 s.
Membrane potentials and the energetics of intestinal Na+-dependent transport systems
Authors: Kimmich G. A. , Carter-Su C.
Published: December 2017

The transmembrane chemical gradient for Na+ that most living cells maintain represents an energy source which is not sufficient to account for observed cellular sugar or amino acid gradients. This short review summarizes the literature pointing to the above conclusion, and described experimental evidence from a variety of model systems which indicates that the membrane potential can provide an additional driving force. Ordinarily, solute leak pathways compromise the full gradient forming capability of the Na+-dependent concentration systems and obscure the extent to which membrane potentials are important. When these "leaks" are experimentally controlled, solute gradients are established that identify the membrane potential as a quantitatively very important energy input. Furthermore, if the electrochemical gradient for Na+ is the sole source of energy, an extremely high efficiency of energy transduction must occur during gradient-coupled transport. An experimental approach is described here which can provide clues to the mechanistic role for membrane potentials in intestinal Na+-dependent sugar transport.
Binding of aldosterone to cytoplasmic and nuclear receptors of the urinary bladder epithelium of Bufo marinus
Authors: Kusch M. , Farman N. , Edelman I. S.
Published: December 2017

Binding of aldosterone to cytoplasmic and nuclear sites in urinary bladder epithelia of Bufo marinus (Dominican variant) is saturable and dependent upon steroid concentration. Scatchard analysis of specific cytoplasmic binding yielded a maximal binding capacity (N) of 14.5 X 10(-14) mol/mg protein and an apparent equilibrium dissociation constant (Kd) of 1.4 X 10(-8) M. Since Scatchard analysis of specific nuclear binding was complex, this binding was resolved by a computer-generated cirve-fitting technique which analyzed total aldosterone bound. Nuclear binding was resolved into three sites: a nonsaturable site that was linearly dependent upon aldosterone concentration, and two saturable sites (types I and II). Type I sites had relatively low capacity for aldosterone (N = 31 +/- 1 X 10(-14) mol/mg DNA) and high affinity (Kd = 2.5 +/- 0.5 X 10(-9 M); tffininty (Kd = 8.6 +/- 1.7 X 10(-7) M). Competition for [3H]aldosterone binding by dexamethasone, corticosterone, cortisol, progesterone, testosterone, and 17 beta-estradiol demonstrated that type I nuclear sites have higher affinity for aldosterone than for other steroids. The findings are consistent with the inference that the type I site is the mineralocorticoid receptor.
Aldosterone receptor occupancy and sodium transport in the urinary bladder of Bufo marinus
Authors: Farman N. , Kusch M. , Edelman I. S.
Published: December 2017

The concentration dependence of binding of [3H]aldosterone to cytoplasmic and nuclear receptors was evaluated in urinary bladder epithelial cells of Colombian toads. One class of specific sites (sensitive to displacement by excess aldosterone) was detected in the cytosol. However, two classes of specific nuclear [3H]aldosterone binding sites were evident. In the nucleus, high-affinity (Kd = 2.7 X 10(-9) M), low-capacity (N = 15 X 10(-14) mol/mg DNA) sites (type I) were completely saturated at approximately 4 X 10(-8) M aldosterone, a concentration which gave a maximal increase in short-circuit current (SCC). Occupancy of low-affinity (Kd = 4.6 X 10(-7) M), high-capacity sites (N = 150 X 10(-14) mol/mg DNA) (type II) occurred at higher steroid concentrations and did not correlate with further increase in SCC. Binding parameters of Colombian and Dominican variants of Bufo marinus were compared. In both variants, the SCC increase elicited by aldosterone correlated with accumulation of type I complexes in the nucleus, but the relationship was markedly nonlinear. Various alternatives were considered as the basis for a curvilinear dependence of the increment in Na+ transport on abundance of nuclear type I complexes.
Na-K pump and Na-K-ATPase: disparity of their temperature sensitivity
Authors: Willis J. S. , Ellory J. C. , Becker J. H.
Published: December 2017

As previously observed in red blood cells, ouabain-sensitive K influx of kidney cells grown in culture for 3 days was much less inhibited by cooling that Na-K-ATPase of the same cells. (At 5 degrees C K influx was 9.7% of that at 38 degrees C, Na-K-ATPase, 1--2%.) Resealed ghosts of erythrocytes of ground squirrels were made containing 24Na and ATP, and the Na efflux and ATP hydrolysis were measured simultaneously. Under these conditions there was no difference in the reduction of activity with cooling, and the amount of reduction was close to that of active K transport in intact cells. The high sensitivity to temperature, characteristic of broken membranes, could not be induced in intact cells or resealed ghosts by eliminating either the Na/K gradient or the ATP gradient nor by chelation of cellular and extracellular Ca. It could not be eliminated in broken membranes by protection with ATP or Mg. Structural reorganization of membrane during lysis may cause the increase in temperature sensitivity of Na-K-ATPase.
Agonist-induced secretions and potassium release from rat submandibular gland slices
Authors: Bogart B. I. , Picarelli J.
Published: December 2017

Secretory activity induced by stimulation of alpha-adrenergic, beta-adrenergic, and muscarinic cholingeric receptors and by dibutyryl cAMP and 8-bromo cGMP has been investigated in rat submandibular tissue slices. Isoproterenol produced a sialic acid secretion from the acinar cells that was inhibited by propranolol, but not by phenoxybenzamine or atropine. Dibutyryl cAMP produced a sialic acid secretion from the acinar cells that was not inhibited by propranolol, phenoxybenzamine, or atropine. Both norepinephrine and acetylcholine produced significant secretion of sialic acid but at a reduced efficacy. Norepinephrine stimulated both peptide hydrolase secretion from the granular duct cells and a release of K+ from the acinar cells. Both actions were inhibited by phenoxybenzamine, but not by propranolol or atropine. Acetylcholine stimulated a minimal secretion of peptide hydrolase from the granular duct cells and a significant release of K+ from the acinar cells. The norepinephrine- and acetylcholine-stimulated release of K+ was increased after the addition of 1 mM ouabain. High concentrations of 8-bromo cGMP induced a K+ efflux that was not inhibited by phenoxybenzamine or atropine. Vacuolation of the acinar cells was correlated with K+ release.
Contractile properties of rat soleus muscle: effects of training and fatigue
Authors: Fitts Robert H. , Holloszy John O.
Published: December 2017

Page C86: Fitts, Robert H., and John 0. Holloszy. "Contractile properties of rat soleus muscle: effects of training and fatigue." Pages C88 and C89: Figures and legends corrected.
Hyperpolarization in mouse parathyroid cells by low calcium
Authors: Bruce B. R. , Anderson N. C.
Published: December 2017

Intracellular microelectrodes were used to record the resting membrane potential of mouse parathyroid cells in vitro. The mean value of the membrane potential in 2.5 mM calcium was -20 mV. Exposure to low-calcium solutions (1.5 mM) caused rapid hyperpolarization to a mean value of -50 mV. The relationship between extracellular calcium and the membrane potential was sigmoid, and the transition between high and low intracellular potentials occurred between 1.5 mM and 2.25 mM calcium. Magnesium, manganese, and lanthanum reversed the low-calcium hyperpolarization. In 1.5 mM calcium solutions, the relationship between external potassium (greater than 10 mM) and the membrane potential was 46 mV per 10-fold change in extracellular potassium. In 2.5 mM calcium solutions, the resting membrane potential was independent of the external potassium concentration. It is concluded that the resting membrane potential of mouse parathyroid cells is highly sensitive to the extracellular concentration of calcium and calcium-like ions. With the low-calcium secretory stimulus, hyperpolarization is accompanied by the development of strong dependence of the resting membrane potential on extracellular potassium levels.
Properties of motor units of the frog iliofibularis muscle
Authors: Luff A. R. , Proske U.
Published: December 2017

The tension developed by single motor units of the iliofibularis muscle of the frog Litoria aurea was recorded in response to single-shock and repetitive stimulation of motor axons. The majority of units in each muscle, 13 on the average, were of the twitch type; an additional 4 units were slow or tonic. It appeared that slow units comprised a single homogeneous population, but two types of twitch units could be recognized: small fatigue-resistant units with long twitch times to peak (20--40 ms) and larger, fatigable units with briefer times to peak (16--27 ms). Evidence from a comparison of unit tetanic tensions indicated the presence of polyneuronal innervation of both slow and twitch muscle fibers. The relatively low incidence of polyneuronal innervation of twitch fibers in iliofibularis, when compared with a muscle like sartorius (9), was attributed to the difference in lengths of muscle fibers in the two muscles. It was argued that slow muscle fibers probably receive a multiterminal as well as polyneuronal innervation, with the terminals of any one axon lying widely spaced along the muscle fiber.
Effect of microvibration on activity of ureteral and portal smooth muscles
Authors: Ohhashi T. , Azuma T. , Sakaguchi M.
Published: December 2017

Spontaneous contractions were elicited by microvibrations (1--80 Hz, 50--400 micron) imposed upon quiescent ureter and portal venous smooth muscles of dogs. The microvibrations increased the rate of spontaneous contractions. A microvibration of larger amplitude gave rise to a more profound increase at each frequency. The acceleration was often accompanied by a reduction in contractile force. The positive chronotropic effect was enhanced by increases in frequency from 20 to 40 Hz and not affected by administration of autonomic blocking agents and tetrodotoxin, but disappeared in a Ca-free environment and reappeared on addition of Ba2+. the simulating action of microvibration was almost proportional to external Ca2+ concentrations ranging from 2.2 to 6.2 mM. The microvibrations were able to elicit spontaneous activity in the preparation, which had been made quiescent by administration of Mn2+. These findings suggested that the positive chronotropic effect may be closely related to an increased Ca2+ influx through the membrane of smooth muscle. Active tension in the ureter in a state of contracture was depressed by imposed microvibrations.
Effect of ammonium chloride on osmotic behavior of red cells in nonelectrolytes
Authors: Sass M. D.
Published: December 2017

Ammonium chloride, demonstrated to be a permeating electrolyte for human red cells in water or sodium chloride solutions, has been shown to act as if it contributes osmotic support in the presence of sucrose. The additional protection provided by ammonium chloride against hemolysis in hypotonic sucrose was found to approximate the milliosmolar concentration of the added salt. In view of previous suggestions that potassium loss was responsible for the increased protection observed with hypotonic nonelectrolyte alone, it was considered reasonable that the further protection afforded by ammonium chloride might reflect a comparable mechanism. Such a relationship was not observed. When added to isosmotic sucrose, ammonium chloride was found to be as effective as sodium chloride in preventing rather than augmenting potassium loss, in accord with the observations of others. Under hypotonic conditions, however, the addition of ammonium chloride had no effect on potassium loss beyond that observed in hypotonic sucrose alone. Equivalent additions of sodium chloride eliminated the potassium loss entirely. It was concluded that sucrose, and possibly other nonelectrolytes, acted to modify the red cell's permeability to ammonium chloride. It is this conversion of ammonium chloride to an impermeant molecule that is considered to be responsible for the observed osmotic support as well as for the markedly disparate findings in sodium chloride solutions.
Electrical activity of rat myocardial cells in culture: La3+-induced alterations
Authors: Kitzes M. C. , Berns M. W.
Published: December 2017

Intracellular analysis of neonatal rat (1–2 day old) ventricular cells in culture shows that contracting myocardial cells exhibit an array of different patterns of spontaneous electrical activity. Resting membrane potentials varied between -40 mV and -98 mV. Our results indicate that some cultured cells show resting membrane potentials, overshoot, and total spike amplitude values comparable to those normally found in neonatal and adult rat heart. A low ratio of pacemaker (40%) to nonpacemaker cells (60%) and low incidence of hyperpolarizing after-potentials (35%) were found. La3+application (0.1–4.0 mM) induced progressive cell depolarization, concomitant diminution in discharge frequency, and marked alteration of action potential configuration. A parallel decline in frequency and strength of rhythmic contractions was observed. Abolition of contractility occurred only in association with depolarization and complete disappearance of action potentials. Recovery of electrical and contractile activity followed medium replacement. Our results indicate that La3+ does not act as a specific excitation-contraction (E-C) uncoupler in the cultured cells but has multiple effects upon their normal electrical characteristics.