bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological Control of Molluscan Gill Cilia by 5-Hydroxytryptamine
Authors: Gosselin R. E. , Moore K. E. , Milton A. S.
Published: May 2004

An examination is made of the hypothesis that endogenous 5-hydroxytryptamine (5-HT) serves as a local hormone regulating ciliary activity in the lamellibranch gill. These cilia are sensitive to exogenous 5-HT and respond to it by a prompt, sustained, and reversible rise in beat frequency; at the same time the carbohydrate metabolism is stimulated, as described elsewhere. Control gill contains small but definite amounts of endogenous 5-HT according to bioassay, fluorometry, and chromatography. The amount can be increased markedly by exposing the isolated gill to the precursor substance 5-hydroxytryptophan but not l-tryptophan. As the tissue level of 5-HT rises, the spontaneous beat frequency also rises. Both remain elevated for hours and perhaps for days. The gill of Mytilus edulis is richer than the gill of Modiolus demissus in both endogenous 5-HT and effective 5-hydroxytryptophan decarboxylase activity. Modiolus gill lacks the 5-hydroxyindole oxidase by which Mytilus gill destroys 5-HT. What if any mechanism exists in Modiolus for degrading 5-HT is not known, but monoamine oxidase is not present. The 5-HT content of Mytilus and Modiolus gill cannot be modified by treatment with reserpine or α-methyl-dopa. Which cells of the gill synthesize and destroy 5-HT has not been established, but these observations support the concept that the physiological activity of lamellibranch gill cilia is controlled by a serotonergic mechanism.
Cation-Anion Balance during Potassium and Sodium Absorption by Barley Roots
Authors: Jackson P. C. , Adams H. R.
Published: May 2004

Steady-state rates of potassium ion and sodium ion absorption by excised barley roots accompanied by various anions were compared with the rates of anion absorption and the concomitant H+ and base release by the roots. The cation absorption rates were found to be independent of the identities, concentrations, and rates of absorption of the anions of the external solution, including bicarbonate. Absorption of the anion of the salt plus bicarbonate could not account for the cation absorption. H+ is released during cation absorption and base during anion absorption. The magnitude by which one or the other predominates depends on the relative rates of anion and cation absorption under various conditions of pH, cation and anion concentration, and inhibitor concentrations. The conclusion is that potassium and sodium ions are absorbed independently of the anions of the absorption solution in exchange for H+, while anions are exchanged for a base. The H+ release reflects a specificity between K+ and Na+ absorption such that it appears to be H+ exchanged in the specific rate-limiting reactions of the cation absorption.
The Role of the Gut in Albumin Catabolism
Authors: Franks J. J. , Mosser E. L. , Anstadt George L.
Published: May 2004

I131-albumin metabolic studies were carried out in 5 rabbits before, 3 weeks after, and several months after removal of 70 to 90 per cent of the jejunum and ileum. A sixth animal was studied before and 11 weeks after a sham operation. During postoperative experiments, the animals were found to be in a highly unsteady state with large losses of albumin from the vascular compartment. Despite these losses, the plasma albumin concentration was maintained at a relatively constant level. No decrease in the albumin efflux occurred following nearly complete jejuno-ileectomy. The data suggest that albumin catabolism is a first order process.
The Electrical Characteristics of Active Sodium Transport in the Toad Bladder
Authors: Frazier Howard S. , Leaf Alexander
Published: May 2004

The mechanism responsible for active sodium transport in the urinary bladder of the toad appears to be located at the serosal boundary of the epithelial cell layer of the bladder. Studies of the potential step observed at the serosal boundary in the open-circuited state were undertaken in an attempt to define the factors responsible for its production. Glass micropipettes were used to measure the serosal potential step in bladders exposed on the serosal side to solutions of high potassium or of high potassium and low chloride concentration. Observed potentials exceed the maximum values which would have been expected if the serosal potential step were a potassium or chloride diffusion potential. Measurements of net cation flux exclude the possibility of a diffusion potential at this border due to the passive movement of any anionic species. The observed independence of transbladder potential and short-circuit current from the pH of the serosal medium over a wide range of pH makes it unlikely that the observed serosal potential step is a hydrogen ion diffusion potential. We conclude that the active sodium transport mechanism in toad bladder is "electrogenic."
The Role of Potassium in Active Transport of Sodium by the Toad Bladder
Authors: Essig Alvin , Leaf Alexander
Published: May 2004

Studies were carried out on the isolated urinary bladder of the toad, Bufo marinus, in order to explain the dependence of active sodium transport on the presence of potassium, in the serosal medium. Attempts to obtain evidence for coupled sodium-potassium transport by the serosal pump were unsuccessful; no relation between sodium transport and uptake of K42 from the serosal medium was demonstrable. Rather, the predominant effect of serosal potassium appeared to be operative at the mucosal permeability barrier, influencing the permeability of this surface to sodium. The mucosal effects of serosal potassium were correlated with effects on cellular cation content. When sodium Ringer's solution was used as serosal medium, removal of potassium resulted in significant decrease in tissue potassium content, commensurate increase in tissue sodium content, and marked depression of mucosal permeability and sodium transport. When choline replaced sodium in the serosal medium, removal of potassium resulted in only slight alterations of tissue electrolyte content, and effects on mucosal permeability and sodium transport were minimal.
Immunochemical Studies on the Components of the Pepsinogen System
Authors: Van Vunakis Helen , Lehrer Harris I. , Allison William S. , Levine Lawrence
Published: May 2004

Rabbit antisera to pepsin and pepsinogen were characterized by several immunological criteria. Both antisera inhibited the rennet activity of pepsin. Antipepsinogen protected pepsin from alkaline denaturation. Using antipepsinogen, precipitin analysis at pH 5.5 indicated that the native enzyme resembles the precursor more closely than did the denatured enzyme. However, all three proteins have some antigenic sites in common. Both antisera reacted more efficiently with their homologous antigens. When measured by C' fixation, the pepsinogen-antipepsinogen system was inhibited by pepsin and to a greater degree, by the activation mixture and the pepsin-inhibitor complex. Pepsin-antipepsin was inhibited by pepsinogen. The specificity of these two antibodies toward pepsin and pepsinogen conformation was used to measure the disappearance of pepsinogen and the concomitant appearance of pepsin during autocatalytic conversion at pH 4.6. The experimental results obtained during the conversion could be duplicated by using varying proportions of pepsin and pepsinogen in the model system. The potentialities of employing these antisera to detect conformational changes such as the unmasking of the pepsin moiety in pepsinogen molecules modified by physical or chemical reagents are discussed.
Structurally Caused Freezing Point Depression of Biological Tissues
Authors: Bloch Rene , Walters D. H. , Kuhn Werner
Published: May 2004

When investigating the freezing behaviour (by thermal analysis) of the glycerol-extracted adductor muscle of Mytilus edulis it was observed that the temperature of ice formation in the muscular tissue was up to 1.5°C lower than the freezing point of the embedding liquid, a 0.25 N KCl solution with pH = 4.9 with which the tissue had been equilibrated prior to the freezing experiment. A smaller freezing point depression was observed if the pH values of the embedding 0.25 N KCl solution were above or below pH = 4.9. Reasoning from results obtained previously in analogous experiments with artificial gels, the anomalous freezing depression is explained by the impossibility of growing at the normal freezing temperature regular macroscopic crystals inside the gel, due to the presence of the gel network. The freezing temperature is here determined by the size of the microprisms penetrating the meshes of the network at the lowered freezing temperature. This process leads finally to an ice block of more or less regular structure in which the filaments are embedded. Prerequisite for this hindrance of ideal ice growth is a sufficient tensile strength of the filamental network. The existence of structurally caused freezing point depression in biological tissue is likely to invalidate many conclusions reported in the literature, in which hypertonicity was deduced from cryoscopic data.
Calcium Flux in the Mammalian Ventricular Myocardium
Authors: Langer G. A. , Brady A. J.
Published: May 2004

The exchange of Ca45 was studied in dog myocardium by means of a newly developed perfusion technique whereby an excised papillary muscle was perfused through its own artery. This makes possible the sequential and simultaneous correlation of ionic flux with ventricular myocardial function with each muscle serving as its own control. Calcium exchange has the following characteristics: (a) The major component of calcium flux is independent of the frequency of contraction. It demonstrates a rapidly equilibrating phase (half-time, 4 to 6 minutes) and a more slowly equilibrating phase with a progressively decreasing rate constant. The flux characteristics of the more rapidly equilibrating compartment are determined by a factor or factors, in addition to simple diffusion, which increase the time required for this compartment to achieve a steady-state with respect to the vascular compartment. (b) A lesser component of exchange is stimulus-rate dependent and is characterized by an alteration in the rate of calcium turnover such that the altered influx: efflux ratio requires 20 to 25 minutes to achieve equilibrium. After this time, despite the higher stimulus rate, there is no evidence of change in total tissue calcium. (c) The initial rate of the transient response is approximately proportional to the change in stimulus rate.
The Coupling of the Short-Circuit Current to Metabolism in the Urinary Bladder of the Toad
Authors: Maffly Roy H. , Edelman I. S.
Published: May 2004

The relationship of the short-circuit current to metabolism was studied in the toad bladder in vitro. Substrates and inhibitors were added to the bathing medium and the effect on the short-circuit current was determined. The spontaneous decline in the short-circuit current that occurred in substrate-free media was prevented or reversed by the addition of glucose, pyruvate, lactate, or ß-hydroxybutyrate, whereas acetate and tricarboxylic acid cycle intermediates had no effect. A variety of metabolic inhibitors depressed the short-circuit current; depression by iodoacetate and by malonate was delayed by prior addition of pyruvate or lactate but not by glucose. The ability of a substrate to stimulate the current did not correlate with its rate of oxidation to CO2. On the basis of earlier studies, the metabolic effects on the short-circuit current were assumed to reflect equivalent effects on the rate of active Na transport. It is suggested that the energy for Na transport is provided not by a general cellular metabolic pool but by a specific metabolic pathway or pathways spatially linked to the transport mechanism.
The Spread of Excitation among Neurons in the Heart Ganglion of the Stomatopod, Squilla oratoria
Authors: Watanabe Akira , Takeda Kimihisa
Published: May 2004

Neurons in the heart ganglion of the mantis shrimp (a stomatopod crustacean) are functionally tightly linked together. The extracellular action potential from the whole trunk very often shows a complex form, but the response is all-or-none to the applied stimulus, indicating that the excitation in one neuron spreads very rapidly to all others. Application of isotonic MgCl2 solution or repetitive stimulation sometimes separates the spike into its components. The resting potential of the soma membrane is 50 to 60 mv. External stimulation elicits a spike of 60 to 80 mv amplitude with a step on its rising phase. Hyperpolarization reveals one more inflection on the rising phase. These inflections divide the soma action potential into three parts, A1, A2, and B spikes in that order from the foot. The B spike disappears on increasing the hyperpolarization, but A1 and A2 remain, indicating that B originates from the soma membrane, whereas A1 and A2 originate from the two axons of the bipolar cell. Thus the impulse invades the soma from two directions, one from the stimulated side, the other from the other side via the "parallel axons" and the "side-connections;" the latter are presumed to interconnect the axons. When the parallel axons are cut, conduction takes place across the soma with a greatly reduced safety factor and a prolonged conduction time. Neuron-to-neuron transmission takes place in either direction.
Electrophysiology of an Insect Heart
Authors: McCann Frances V.
Published: May 2004

Bioelectric activity in single cells of the moth myocardium has been measured in situ with intracellular microelectrodes with particular reference to the bizarre ionic medium which bathes the tissues. Resting potentials averaged 47 mv, inside negative with respect to outside, despite a value of 11 mv calculated on the basis of transmembrane potassium concentration gradients. Action potentials overshoot as much as 12 mv in the virtual absence of extracellular sodium. Two "types" of action potentials have been recorded; one that resembles vertebrate atrial action potentials is found in the cephalic region of the tubular heart, and the other, similar in contour to vertebrate ventricular action potentials, is found in the areas posterior to the first abdominal segment. Histological sections indicate no structural differences between the two areas. Typical cardiac pacemaker type potentials occur but are not topographically localized. The effects of the omission from the perfusion fluid of the four major cationic constituents, Na+, K+, Ca++ and Mg++, on resting and action potentials may be summarized as: no effect, hyperpolarization, prolonged repolarization, and depolarization, respectively.
Proline Control of the Feeding Reaction of Cordylophora
Authors: Fulton Chandler
Published: May 2004

The colonial hydroid Cordylophora is a carnivore whose feeding is induced by substances released from captured prey. An active molecule, probably the only one, has been isolated from a fraction of the laboratory food of Cordylophora, brine shrimp larvae, and identified on paper chromatograms as the imino acid proline. Reagent proline induces the feeding reaction at 10-5 M. The reaction is specific in that only two α-imino acids very closely related to proline were found to possess significant activity: azetidine-2-carboxylic acid and pipecolic acid. The response to proline is inhibited by magnesium ions and enhanced by phosphate. Since previous studies have shown that the feeding reactions of Hydra, Physalia, and Campanularia are controlled by reduced glutathione, the phylogenetic implications of the proline control of feeding in Cordylophora are discussed. The feeding reactions of both Cordylophora and Hydra are also induced by proteases, suggesting similar mechanisms of induction in the two hydroids.
Interactions of Arsenate with the Phosphate-Transporting System of Yeast
Authors: Rothstein Aser ,   with the technical assistance of Katherine Donovan
Published: May 2004

Arsenate competes with phosphate for transport into the yeast cell. The affinity of the two substances for the transport system is about equal, but in mixtures the phosphate is taken up about twice as fast as arsenate, because the maximal transport rate for phosphate is about twice as high. In addition to the competitive effect, arsenate causes a continuous and irreversible inactivation of the transport system that can be characterized by first order kinetics. The rate of arsenate inactivation is slower in the presence of phosphate and the amount of arsenate taken up before complete block is established is also decreased. The inactivation of the transport system cannot be relieved by washing or by treatment with glucose and phosphate. The inactivation is not the result of an inhibition of metabolism.
The L-Amino Acid Oxidase from Silkworm Eggs (Bombyx mori L.)
Authors: Kotaka Sadao
Published: May 2004

An enzyme which catalyzes the oxidation of L-amino acids has been isolated from silkworm eggs (Bombyx mori L.), and purified. The activity of the enzyme preparation is about 1584 times more than that of the crude preparation. Methods of purification of the enzyme are described in detail and certain physicochemical properties of the enzyme are also described.
The Nature of the Muscle-Relaxing Factor
Authors: Briggs F. Norman , Fuchs Franklin
Published: May 2004

Analysis of the effects of deoxycholate and benzalkonium chloride on granule relaxing activity, myofibril and glycerinated fiber responses to ATP, and the sensitivity of these actomyosin-containing systems to relaxing factors have established that it is possible to differentially inactivate intrinsic granule relaxing factor. It is therefore possible to use these agents to treat myofibrils and glycerinated muscle fibers so that they may be used for the assay of muscle-relaxing factor preparations. The destruction of intrinsic relaxing factor can be produced by treating actomyosin with 1 mM deoxycholate or 0.005 per cent benzalkonium chloride for 5 minutes at room temperature.
Neural and Photochemical Mechanisms of Visual Adaptation in the Rat
Authors: Dowling John E.
Published: May 2004

The effects of light adaptation on the increment threshold, rhodopsin content, and dark adaptation have been studied in the rat eye over a wide range of intensities. The electroretinogram threshold was used as a measure of eye sensitivity. With adapting intensities greater than 1.5 log units above the absolute ERG threshold, the increment threshold rises linearly with increasing adapting intensity. With 5 minutes of light adaptation, the rhodopsin content of the eye is not measurably reduced until the adapting intensity is greater than 5 log units above the ERG threshold. Dark adaptation is rapid (i.e., completed in 5 to 10 minutes) until the eye is adapted to lights strong enough to bleach a measurable fraction of the rhodopsin. After brighter light adaptations, dark adaptation consists of two parts, an initial rapid phase followed by a slow component. The extent of slow adaptation depends on the fraction of rhodopsin bleached. If all the rhodopsin in the eye is bleached, the slow fall of threshold extends over 5 log units and takes 2 to 3 hours to complete. The fall of ERG threshold during the slow phase of adaptation occurs in parallel with the regeneration of rhodopsin. The slow component of dark adaptation is related to the bleaching and resynthesis of rhodopsin; the fast component of adaptation is considered to be neural adaptation.
Electrolyte Metabolism in HeLa Cells
Authors: Wickson-ginzburg Margaret , Solomon A. K.
Published: May 2004

Methods have been developed to study cellular Na, K, and Cl concentrations in HeLa cells. Cell [Na] and [K] are functions of the age of the culture. As the culture grows [K], expressed in mmols/liter cell H2O, rises from an initial value of 121 to a peak of 206 at about 4 days, and thereafter falls until it has almost returned to the initial value by the 9th day. [Na] falls as [K] rises, but there is no fixed relationship between the cellular concentrations of the two cations. There is, however, a correlation between generation time and cellular [K]. Measurements of net K uptake and net Na extrusion were carried out during 1 hour incubation at 37°C of low K cells. Both net K uptake and net Na extrusion took place against chemical concentration gradients, so that at least one transport system must be active; if the Cl distribution is passive both net K uptake and net Na extrusion are active. Studies with inhibitors of respiration and glycolysis lead to the conclusion that respiration is not required for these net transports, which appear to derive their energy from glycolytic sources.
Linear Relations between Stimulus Amplitudes and Amplitudes of Retinal Action Potentials from the Eye of the Wolf Spider
Authors: DeVoe Robert D.
Published: May 2004

Incremental photic stimuli have been used to elicit small amplitude retinal action potentials from light-adapted ocelli of the wolf spider, Lycosa baltimoriana (Keyserling) in order to see whether or not the amplitudes of these potentials are linearly related to the stimulus amplitudes. Sine wave variations of light intensity around a mean elicit sine wave variations in potential which contain inappreciable harmonics of the stimulus frequency and whose amplitudes are linearly related to the stimulus amplitudes. Likewise, the responses to the first two periodic Fourier components of incremental rectangular wave stimuli of variable duty cycle are directly proportional to the amplitudes of these components and have phases dependent only on the frequencies and phases of these components. Thirdly, a linear transfer function can be found which describes the amplitudes and phases of responses recorded at different frequencies of sine wave stimulation and this transfer function is sufficient to predict the responses to incremental step stimuli. Finally, it is shown that flash response amplitudes are linearly related to incremental flash intensities at all levels of adaptation. The relations of these linear responses to non-linear responses and to physiological mechanisms of the eye are discussed.
Inhibition of Caffeine Rigor and Radiocalcium Movements by Local Anesthetics in Frog Sartorius Muscle
Authors: Feinstein Maurice B.
Published: May 2004

Local anesthetics have been found to act as competitive inhibitors of caffeine in frog sartorius muscle. They block caffeine-induced rigor and the attendant increase in Ca45 influx and efflux. Increased net uptake of sodium, loss of potassium, and concurrent increase in oxygen consumption are all effectively blocked by procaine. Evidence is presented that the inhibitory effect of the local anesthetics cannot be explained by the formation of molecular complexes with caffeine. Increased efflux of Ca45 produced by changing from zero calcium Ringer's to 0.1 mM or 1 mM calcium Ringer's is inhibited by procaine and tetracaine. EDTA-stimulated calcium efflux is not affected by either local anesthetic. Caffeine rigor develops in frog muscle depolarized with KCl or rendered electrically inexcitable by sodium lack. Both the rigor and the increased calcium fluxes are inhibited by local anesthetics in depolarized muscle.
The Photosensitive Retinal Pigment System of Gekko gekko
Authors: Crescitelli Frederick
Published: May 2004

Retinal extracts of Gekko gekko were found to contain two retinene1 photopigments, one with maximum absorption at about 521 mµ, the second with a maximum in the region of 478 mµ. These pigments were assayed by the method of partial bleaching and their spectral characteristics studied by examining their difference spectra. The 478 mµ pigment was present in the extracts as 8 per cent of the total photopigment concentration. The two pigment systems were shown to be biochemically independent and to have different properties. Unlike the 521 mµ pigment, for example, the 478 mµ pigment was found to resist the action of NH2OH and, within the cells, to be unaffected by sucrose solutions. These solutions destroyed or altered the 521 system so that extracts of sucrose-treated retinae were found to contain significantly less 521 photopigment. In digitonin solution the 521 pigment was unaffected by sucrose treatment. Both pigments were extracted from separated, washed outer segments and so are considered to be visual pigments. This dual system accounts for the spectral sensitivity of this gecko as determined by Denton. A search was made, but no evidence was secured for the presence of a photopigment absorbing at longer wavelengths. Electoretinographic data suggest, however, that an elevated sensitivity at longer wavelengths occurs in some geckos so that a continued search is justified for a third photopigment.
Post-Tetanic Repetitive Activity in the Cat Soleus Nerve
Authors: Standaert Frank G.
Published: May 2004

Subsequent to conditioning by a high frequency stimulus axons of the cat soleus nerve respond to single stimuli with brief trains of repetitive action potentials. This phenomenon, post-tetanic repetitive activity (PTR), was studied in individual axons and single motor units of an in situ cat soleus nerve-muscle preparation. The occurrence, intensity, and duration of PTR are principally dependent on the frequency and duration of the conditioning tetanus. PTR occurs synchronously in the axon and muscles of single motor units. An analysis of the temporal relationships of the repetitive nerve and muscle potentials showed that PTR is generated in the motor nerve terminal. It is postulated that PTR is produced by a generator potential which is developed in the post-tetanic period between the unmyelinated nerve terminal and the last node of Ranvier.
Tautomeric Forms of Metarhodopsin
Authors: Matthews Rowena G. , Hubbard Ruth , Brown Paul K. , Wald George
Published: May 2004

Light isomerizes the chromophore of rhodopsin, 11-cis retinal (formerly retinene), to the all-trans configuration. This introduces a succession of unstable intermediates—pre-lumirhodopsin, lumirhodopsin, metarhodopsin —in which all-trans retinal is still attached to the chromophoric site on opsin. Finally, retinal is hydrolyzed from opsin. The present experiments show that metarhodopsin exists in two tautomeric forms, metarhodopsins I and II, with λmax 478 and 380 mµ. Metarhodopsin I appears first, then enters into equilibrium with metarhodopsin II. In this equilibrium, the proportion of metarhodopsin II is favored by higher temperature or pH, neutral salts, and glycerol. The change from metarhodopsin I to II involves the binding of a proton by a group with pK 6.4 (imidazole?), and a large increase of entropy. Metarhodopsin II has been confused earlier with the final mixture of all-trans retinal and opsin (λmax 387 mµ), which it resembles in spectrum. These two products are, however, readily distinguished experimentally.
Cation Transport in Escherichia coli
Authors: Schultz Stanley G. , Epstein Wolfgang , Solomon A. K.
Published: May 2004

The resuspension of K-poor, Na-rich stationary phase E. coli in fresh medium at pH 7.0 results in a rapid uptake of K and extrusion of Na by the cells. In all experiments net K uptake exceeded net Na extrusion. An investigation of the uptake of glucose, PO4, and Mg and the secretion of H by these cells indicates that the excess K uptake is not balanced by the simultaneous uptake of anions but must be accompanied by the extrusion of cations from the cell. The kinetics of net K uptake are consistent with the existence of two parallel influx processes. The first is rapid, of brief duration, and accounts for approximately 60 per cent of the total net K uptake. This process is a function of the extracellular K concentration, is inhibited in acid media, and appears to be a 1 for 1 exchange of extracellular K for intracellular H. The second influx process has a half-time of approximately 12 minutes, and is not affected by acid media. This process is a function of the intracellular Na concentration, is dependent upon the presence of K in the medium, and may be ascribed to a 1 for 1 exchange of extracellular K for intracellular Na.
Vitamin A in the Vision of Insects
Authors: Goldsmith Timothy H. , Warner Lana T.
Published: May 2004

Acetone-methanol extracts of honeybees (Apis mellifera) were chromatographed from petroleum ether on columns of aluminum oxide and magnesium oxide:celite. Vitamin A1 was identified by the Carr-Price (antimony chloride) reaction. These experiments provide the first demonstration of vitamin A in the tissues of an insect. Like retinene, vitamin A is confined to the heads and is not found in either thoraces or abdomens. Dark-adapted bees have very little vitamin A. During light adaptation the vitamin A increases, but at the expense of retinene, which decreases. As much as 0.1 µg of vitamin A/gm of heads has been recovered from light-adapted bees. Two methods are described for demonstrating the enzymic reduction of retinene to vitamin A, using an extract of the heads of honeybees.
Cat Heart Muscle In Vitro
Authors: Page Ernest , Goerke R. J. , Storm S. R.
Published: May 2004

Cellular concentrations, [K]i, [Na]i, and [Cl]i, and cell water contents were measured in vitro at 27°C in cat papillary muscles. Measurements were made with and without ouabain at varying concentrations of K and ouabain, at pH 5.2 and 9.0, in absence of O2, and in NaCl-free solution. Large losses of cell K and increases of cell Na occurred in presence of ouabain, at 2–3°C, and in K-free medium. The dependence of inhibition of cation transport by ouabain on external K concentration, studied at constant initial [K]i, was consistent with a competition between K and ouabain localized to the external face of the membrane. In NaCl-free sucrose solution [K]i remained at its physiological value and was not affected by exposure to ouabain or low temperature, except when Ca was also omitted. Ouabain inhibition persisted at pH 9.0 and in Ca-poor media. Cells swelled and lost K at pH 5.2, and residual ouabain effect was small. At pH 9.0, or in absence of O2, or in Ca-poor solutions cells became permeable to mannitol. The ion movements observed after inhibition of active transport are compatible either with a passive K distribution and a primary inhibition of Na extrusion or with inhibition of a coupled active transport of both K and Na.
Electrical Excitability of Isolated Frog Skin and Toad Bladder
Authors: Finkelstein Alan
Published: May 2004

When current of proper polarity and sufficient intensity is passed across isolated frog skin or toad bladder, an action potential of about 200 mv and 10 msec. duration with a sharp threshold and refractory period of several seconds' duration is elicited. Interruption of current during the action potential abolishes the response, and, as shown by appropriate bridge measurements, this occurs because the action potential results from resistance variations during the current flow. The ionic composition of the medium bathing the frog skin was varied, and it was found that the response is relatively insensitive to changes in the solution bathing the inner surface, but rapidly and reversibly affected by changes in the outer solution, particularly by replacement of sodium with potassium and by variations of calcium concentration. It was also observed that the resistance of the skin and action potential across it are reversibly altered by metabolic inhibitors and that these alterations occur independently of any changes in the intrinsic EMF of the system. From the finding that the action potential across frog skin and toad bladder results from a time-variant resistance, it is argued that this same phenomenon can be the basis of electrical excitability in general. This would attribute physical significance to the equivalent circuit commonly employed to represent the plasma membrane; i.e., the plasma membrane would be a mosaic structure of spatially separate permselective regions.
Tracer and Non-Tracer Potassium Fluxes in Frog Sartorius Muscle and the Kinetics of Net Potassium Movement
Authors: Sjodin R. A. , Henderson E. G.
Published: May 2004

Experiments were performed to test the applicability of permeability kinetics to whole frog sartorius muscle using K42 ions as tracers of potassium flux. The whole muscle was found to obey closely the kinetic laws expected to hold for single cellular units in which the potassium fluxes are membrane-limited and intracellular mixing is rapid enough not to introduce serious error. In a 5 mM K Ringer's solution, potassium efflux was very nearly equal to influx when the rate constant for K42 loss was applied to the whole of the muscle potassium. Over a fairly wide range of external potassium concentration, the assumed unidirectional fluxes measured with tracer K42 showed good agreement with net potassium changes determined analytically. The specific activity of potassium lost from labeled muscles to an initially K-free Ringer's solution was measured as a test of the adequacy of intracellular mixing. The results were those expected for a population of cells with uniformly distributed intracellular K42. A small deviation was encountered which can be attributed either to a dispersion of fiber sizes in the sartorius or to a possible small additional cellular compartment in each individual fiber. The additional cellular compartment, should it exist, contains from 0.5 to 1 per cent of the muscle potassium. This is evidently not large enough to interfere seriously with the applicability of permeability kinetics to the whole muscle.
The Effect of Light on the Geotropic Responses of Phycomyces Sporangiophores
Authors: Dennison David S.
Published: May 2004

The geotropic responses of Phycomyces sporangiophores were studied under varying intensities of illumination, using a low speed centrifuge and a fixed beam of blue light. This light has a strongly inhibitory effect on the transient geotropic response, reducing it to 36 per cent of its magnitude in darkness. The inhibition does not vary systematically with light intensity over a range of 400-fold. The light sensitivity of the transient geotropic response thus differs from the light-growth response system, which shows the same growth rate in light and darkness. By contrast, the slower long term geotropic response is enhanced by light of moderate intensities, but is strongly inhibited by high intensities. At and above a mean intensity of about 1 µw/cm2, the long term response is completely removed. If the intensity is lowered from an inhibitory level, either to darkness or to a low level, the geotropic response appears after a time lag of 20 minutes. Furthermore an increase in intensity from one level to another, both levels normally enhancing, results in a transient reversal in the long term geotropic response, also after a time lag of 20 minutes. Thus it is suggested that light is acting at some intermediate step in the long term geotropic sensory system, a step that normally requires 20 minutes for completion.
Electrical Potential Profile of the Toad Skin Epithelium
Authors: Whittembury Guillermo
Published: May 2004

The electrical potential profile of the isolated toad skin was recorded, in vitro, by impalement with micropipette-electrodes, when both sides of the skin were bathed with sulfate-Ringer. The outer side of the skin was some 110 mv negative with respect to the inner side. Upon impalement from the outer side, two main positive steps of 40 to 70 mv each were found to form the skin potential. The site of measurement of each potential difference was permanently marked in the tissue during recording, by deposition of carmine from the micropipette tip using iontophoresis. Serial histological sections of the skin were prepared and search was then made of the carmine deposits 2 to 6 µ in size, under phase contrast microscopy. By this method the main steps were located at the outer and the inner sides of the stratum germinativum cells. The DC resistances between the micropipette tip and the bathing solutions were measured during the recording of each potential difference. The resistance at the outer side of the stratum germinativum cells, of 1.09 kilohm. cm2, was larger than that at their inner side, of 0.30 kilohm. cm2. The stratum germinativum cells maintained a potential difference of -34 mv during short-circuiting of the skin.
Electrophysiology of the Fetal Spinal Cord
Authors: Naka Ken-Ichi
Published: May 2004

Responses from motoneurons were recorded with microelectrodes, from the spinal cords of kitten fetuses and newborn kittens between 40 days' gestation and a few days after birth. As in the adult animal, intracellularly recorded action potentials by either ortho- or antidromic shocks have two components, "A" and "B" or IS and SD. The action potentials of the adult and immature motoneuron differ mainly in the afterpotentials which are absent in the fetal cell in "good" condition. Repeated stimulation or deterioration of the cell resulted, however, in the appearance of depolarizing and hyperpolarizing afterpotentials. No major differences were found in the mode of anti- or orthodromic invasion of the adult and fetal motoneuron, but the degree of invasion of the soma-dendritic complex may be somewhat less in the fetal cells. The ventral root discharge by dorsal root stimulation could be obtained in the fetus 3 weeks before birth. This reflex discharge was concluded to be monosynaptic. Excitatory postsynaptic potentials, probably monosynaptically activated, could be recorded from inside motoneurons by stimulation of dorsal root or peripheral nerves. The most remarkable change during prenatal development was an increase in the speed and efficacy of the excitatory synaptic potentials which showed a marked change during the last weeks of prenatal life.
Electrophysiology of the Fetal Spinal Cord
Authors: Naka Ken-Ichi
Published: May 2004

Interactions of peripheral inputs to the motoneuron of the kitten fetus as young as 3 weeks prenatal were studied by reflex discharge from the ventral root as well as by recording from single motoneurons. Facilitation was found between two synergists in fetuses 1 to 2 weeks before birth. Intracellular recording showed that the facilitation could be explained by summation of excitatory postsynaptic potentials. Inhibition was found between antagonists in the fetuses 2 to 3 weeks before birth and was accompanied by inhibitory postsynaptic potentials. Recurrent inhibition was very powerful in the fetal spinal cord as shown by large motoneuron hyperpolarization by antidromic stimulation. Cells presumed to be "Renshaw cells" and which responded to both ortho- and antidromic stimulation with repetitive firing were shown in the 2 weeks prenatal fetus. These results lead to the conclusion that there is considerable effective synaptic connection of afferent collaterals already established by the later stage of intrauterine life and that this may be achieved independently of external stimuli.
Factors Affecting the Fluxes of Potassium and Chloride Ions in Nitella translucens
Authors: MacRobbie Enid A. C.
Published: May 2004

A more complete study of ionic concentrations and fluxes in the giant internodal cells of Nitella translucens has been made. The vacuolar concentrations were 76 mM K and 170 mM Cl. The content of the chloroplast layer was 135 mµmoles K/cm2 and 215 mµmoles Cl/cm2; in a layer 9 µ thick these correspond to concentrations of 150 mM K and 240 mM Cl. Such a high level of chloride requires active transport of chloride into the cytoplasm, either at the plasmalemma or at the membranes bounding the cytoplasmic particles; it cannot be achieved by active transport of chloride only at the tonoplast. With concentrations of 0.1 mM K and 1.3 mM Cl outside, the fluxes into the cytoplasm had mean values of 1.0 to 1.4 µµmoles K/cm2sec. and 2.1 to 2.8 µµmoles Cl/cm2sec.; the corresponding fluxes from the cytoplasm to the vacuole were about 110 µµmoles K/cm2sec. and 175 µµmoles Clcm2sec. The transfer of both potassium and chloride to the vacuole under different conditions appeared to be correlated with the uptake of chloride into the cytoplasm. It is suggested that two separate processes are involved in the active accumulation of salts in the vacuole—an active uptake of chloride in the cytoplasm and a subsequent transfer of salt to the vacuole. It may be that the second process involves the formation of small vesicles in the cytoplasm and their subsequent discharge into the central vacuole.
The Influence of Na Concentration on Na Transport across Frog Skin
Authors: Cereijido Marcelino , Herrera Francisco C. , Flanigan William J. , Curran Peter F.
Published: May 2004

The effects of changes in Na concentration of the bathing solutions on some transport and permeability properties of the isolated frog skin have been examined. Rate coefficients for unidirectional Na movements across the two major barriers in the skin have been estimated as functions of Na concentration. The results indicate that the "apparent Na permeability" of the outer barrier of the skin decreases markedly when Na concentration in the outer solution is increased from 7 to 115 mM. The observed saturation of rate of Na transport with increasing Na concentration can be ascribed, in part, to this permeability change rather than to saturation of the transport system itself. Unidirectional Cl flux across the short-circuited skin was not significantly altered by an increase in Na concentration from 30 to 115 mM suggesting that the changes in membrane properties are relatively specific for the Na ion. The results also suggest that the movement of Na across the outer membrane may not be due entirely to simple passive diffusion of free Na ions.
Effect of Detergent on Electrical Properties of Squid Axon Membrane
Authors: Kishimoto Uichiro , Adelman William J.
Published: May 2004

The effects of detergents on squid giant axon action and resting potentials as well as membrane conductances in the voltage clamp have been studied. Anionic detergents (sodium lauryl sulfate, 0.1 to 1.0 mM; dimethyl benzene sulfonate, 1 to 20 mM, pH 7.6) cause a temporary increase and a later decrease of action potential height and the value of the resting potential. Cationic detergent (cetyl trimethyl ammonium chloride, 6 x 10-5M or more, pH 7.6) generally brings about immediate and irreversible decreases in the action and resting potentials. Non-ionic detergent (tween 80, 0.1 M, pH 7.6) causes a slight reversible reduction of action potential height without affecting the value of the resting potential. Both anionic and cationic detergents generally decrease the sodium and potassium conductances irreversibly. The effect of non-ionic detergent is to decrease the sodium conductance reversibly, leaving the potassium conductance almost unchanged.
Selective Inhibition of Potassium Contracture in Presence of Intact Twitch
Authors: Fujino Masahiro , Fujino Sumiko
Published: May 2004

If a sartorius muscle of frog is pretreated for 30 min. with a hyposmotic Ringer's (called "hyposmotic potassium chloride") in which all sodium chloride is replaced by 23 mM potassium chloride, and then is immersed in normal Ringer's for about 40 min., a twitch of normal size can be elicited although the potassium contracture is almost completely abolished. During the time that this selective inhibition of potassium contracture occurs, the action potential and both the size and the speed of depolarization due to potassium are almost the same as in a control muscle that is pretreated for 30 min. with 23 mM potassium chloride under isosmotic conditions and that can give a normal potassium contracture. If a muscle is pretreated not with hyposmotic potassium chloride but with a hyposmotic Ringer's in which the concentration of sodium chloride is reduced to 22 mM, the evoked potassium contracture is inhibited, but to a much smaller degree. The partial replacement of chloride by nitrate in hyposmotic potassium chloride has no influence on the degree of the selective inhibition. If after the pretreatment with hyposmotic potassium chloride the muscle is left in normal Ringer's for about 3 hours, there is considerable recovery of ability to undergo contracture. The mechanism of the selective inhibition is briefly discussed.
The Mechanism of Sodium and Chloride Uptake by the Gills of a Fresh-Water Fish, Carassius auratus
Authors: García Romeu F. , Maetz J.
Published: May 2004

Carassius auratus placed in a dilute sodium chloride solution (400 µM) is able to absorb sodium and chloride ions at very different rates, or to absorb one ion and to lose the other. This is the case not only for fish which have been previously kept in choline chloride or sodium sulfate solutions or deionized water, in order to stimulate their absorption processes, but also in control fish which have not been deprived of sodium or chloride. The absorption of sodium or chloride appears to be unaffected by the presence of a nonpermeant co-ion such as choline or sulfate. Conductivity measurements of the external medium show that during ion uptake the conductivity is constant or increases slowly. This suggests the existence of exchange processes between the ions absorbed and endogenous ions excreted. It is unlikely that potassium or calcium is exchanged for sodium, because of the low permeability of the gills to these ions. Finally, the flux ratios observed for both sodium and chloride ions in the present investigation can only be explained, in relation to their electrochemical gradients across the gills, in terms of active transport.
Glucose Utilization by Chick Embryo Heart Homogenates
Authors: Coffey R. G. , Cheldelin Vernon H. , Newburgh R. W.
Published: May 2004

Homogenates of early chick embryos and homogenates of early chick embryonic hearts utilized the phosphogluconate pathway of glucose catabolism to a greater extent, relative to the glycolytic-Krebs cycle pathway, than did homogenates of hearts from older chick embryos or adult chicks. An abrupt drop in the relative participation by the phosphogluconate pathway in embryo heart homogenates occurs at about 5 to 7 days of incubation. Heart homogenates from adult chicks catabolize glucose almost entirely by the glycolytic-Krebs cycle pathway, with negligible participation by the phosphogluconate pathway.
The Initiation of Spike Potential in Barnacle Muscle Fibers under Low Intracellular Ca++
Authors: Hagiwara Susumu , Naka Ken-ichi
Published: May 2004

Electrical properties of the muscle fiber membrane were studied in the barnacle, Balanus nubilus Darw. by using intracellular electrode techniques. A depolarization of the membrane does not usually produce an all-or-none spike potential in the normal muscle fiber even though a mechanical response is elicited. The intracellular injection of Ca++-binding agents (K2SO4 and K salt of EDTA solution, K3 citrate solution, etc.) renders the fiber capable of initiating all-or-none spikes. The overshoot of such a spike potential increases with increasing external Ca concentration, the increment for a tenfold increase in Ca concentration being about 29 mv. The threshold membrane potential for the spike and also for the K conductance increase shifts to more positive membrane potentials with increasing [Ca++]out. The removal of Na ions from the external medium does not change the configuration of the spike potential. In the absence of Ca++ in the external medium, the spike potential is restored by Ba++ and Sr++ but not by Mg++. The overshoot of the spike potential increases with increasing [Ba++]out or [Sr++]out. The Ca influx through the membrane of the fiber treated with K2SO4 and EDTA was examined with Ca45. The influx was 14 pmol per sec. per cm2 for the resting membrane and 35 to 85 pmol per cm2 for one spike. From these results it is concluded that the spike potential of the barnacle muscle fiber results from the permeability increase of the membrane to Ca++ (Ba++ or Sr++).