bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Studies of White Matter
Authors: McDougal D. B. , Schimke Robert T. , Jones Elizabeth M. , Touhill Elizabeth
Published: May 2004

Methods for measurement of glyceraldehyde-P dehydrogenase, triose-P isomerase, fructose 1,6-diphosphate aldolase, and the DPN-linked and flavin-linked α-glycero-P dehydrogenases in small amounts of tissue have been worked out. These enzymes have been measured in ten tracts in rabbit central nervous system. The activities of all the enzymes measured, except the flavin-linked α-glycero-P dehydrogenase, are present in larger amounts in lightly myelinated than in heavily myelinated tracts, but are relatively low in fibrillar layer of olfactory bulb, which is unmyelinated. Aldolase, like P-fructokinase (measured previously), is especially low in fibrillar layer. Taken together with relatively high 6-P-gluconate dehydrogenase activity found earlier this supports the hypothesis that the pentose-P shunt is particularly active in this tract. The activity of DPN-linked α-glycero-P dehydrogenase is inversely proportional to the lipid content of the myelinated tracts, which suggests that its primary role is not related to lipid synthesis in adult brain. The activities of flavin-linked α-glycero-P dehydrogenase are unrelated to those of the DPN-linked enzyme, which is contrary to expectation if the two enzymes function as partners in the "α-glycerophosphate shuttle."
Erythrocyte Sensitization by Blood Group-Specific Bacterial Antigens
Authors: Springer Georg F. , Horton Richard E.
Published: May 2004

Human and chicken erythrocytes are readily coated in vitro by blood group active protein-lipopolysaccharides and lipopolysaccharides from E. coli O86 and E. coli O128. Serum albumin, α2- and ß-lipoproteins inhibit this sensitization. Blood group B specific agglutination of erythrocytes with B or B-like antigens was obtained with antibodies purified by adsorption on and elution from B erythrocytes. Anti-blood group B and E. coli O86-specific antibodies could be eluted from E. coli O86-coated O erythrocytes. Eel anti-H(O) serum agglutinated O erythrocytes and only those A1B red cells which were coated with blood group H(O) active E. coli products. Blood group active substances specifically inhibited agglutination of lipopolysaccharide-coated erythrocytes by anti-B and anti-H(O) agglutinins. Demonstrable amounts of lipopolysaccharide could only be removed from coated erythrocytes by washing them at elevated temperatures (58°C) in physiological solutions. Red cell sensitization with B active E. coli O86 substances was achieved in vivo in a minority of severely diseased infants and in germ-free and ordinary chicks which were in tourniquet shock after treatment with cathartics. Therefore, a possible mode by which erythrocytes of patients with severe intestinal disorders acquire antigens is the fixation of bacterial substances to their surfaces, if there are not enough of the normally interfering plasma factors present.
Some Effects of Calcium Ions on the Action Potential of Single Nodes of Ranvier
Authors: Ulbricht Werner
Published: May 2004

Action potentials of single frog nerve fibers were recorded with the air-gap method in "low Ca" (0.26 mM) and "high Ca" (4.2 mM) solutions and compared to spikes in normal Ringer's (1.05 mM Ca). On increasing (Ca)o the action potentials became shorter, the "knee" during the falling phase as well as the threshold for abolition moved to internal potentials more positive, and the spike recovery during the relative refractory period was faster. Outward current pulses applied during an action potential affected its configuration more in low Ca than in high Ca. The onset of the delayed rectification (in the absence of Na) was found faster in high Ga. After-potentials during anelectrotonus declined more rapidly in high Ca than in low Ca. The results are compared primarily with the voltage-clamp analysis of Ca effects on squid axons and satisfactory qualitative agreement is reached.
The Role of Polyphosphates in the Transport Mechanism of Glucose in Yeast Cells
Authors: Van Steveninck J. , Booij H. L.
Published: May 2004

Several cations inhibit anaerobic fermentation of glucose by intact yeast cells. Some ions (e.g. Hg++) penetrate into the cytoplasm and cause an irreversible inhibition of fermentation. Other ions (e.g. UO2++, Ni++, and Co++) are reversibly bound to a substance at the outside of the yeast cell identified as polyphosphate. Although the cations are bound to exactly the same extent, their influences on fermentation differ greatly. Thorium ions are bound not only to the polyphosphates, but in addition, to phosphatides in the cell membrane. Under circumstances in which glucose is transported into the cell, the amount of polyphosphate in the outer face of the membrane decreases considerably. If yeast is poisoned with monoiodoacetate, the number of glucose molecules that can still be taken up equals the original number of cation-binding sites at the outer surface of the membrane. These data suggest that one molecule of glucose is taken up in connection with the disappearance of one polyphosphate monomer. The hypothesis is framed that the uptake of glucose into the yeast cell is associated with an enzymic phosphorylation (possibly of the carrier), with polyphosphate as phosphate donor. The inhibition of glucose uptake caused by certain metal ions may be the consequence of induced changes in the spatial arrangement of polyphosphate chains; the greater the change in configuration, the larger is the inhibition.
Autoradiographic Studies of Intracellular Calcium in Frog Skeletal Muscle
Authors: Winegrad Saul
Published: May 2004

Autoradiographs consisting of a 1000 A thick tissue section and a 1400 A thick emulsion film have been prepared from frog toe muscles labeled with Ca45. The muscles had been fixed with an oxalate-containing osmium solution at rest at room temperature, at rest at 4°C, during relaxation following K+ depolarization or after prolonged depolarization. From 6 to 39 per cent of K+ contracture tension was produced during fixation. The grains in the autoradiographs were always concentrated in the center 0.2 to 0.3 µ of the I band and the region of the overlapping of the thick and thin filaments. The greater the tension produced during fixation, the greater was the concentration in the A band and the smaller the concentration in the I band. Autoradiographs of two muscles fixed by freeze-substitution resembled those of muscles which produced little tension during osmium fixation. Muscles which shortened during fixation produced fewer grains. In the narrow (<2.0 µ) sarcomeres of the shortened muscles, grain density decreased with decreasing sarcomere width. A theoretical analysis of the significance of these grain distributions is proposed and discussed.
Excitability Changes of the Mauthner Cell during Collateral Inhibition
Authors: Fukami Y. , Furukawa T. , Asada Y.
Published: May 2004

Excitability changes during collateral inhibition of the goldfish Mauthner cell (M cell) were measured directly by stimulating the cell with current pulses applied through an intracellular electrode. Excitability was suppressed during the extrinsic hyperpolarizing potential (EHP) as well as during the collateral IPSP. The inhibitory effect of the EHP was shown to be comparable in intensity to the effect of the IPSP. Excitability changes in the M cell during collateral IPSP depended on changes in the membrane conductance as well as in the membrane potential. Some simple equations are advanced which describe the excitability change during the IPSP in terms of changes in membrane potential and conductance. It was also found that invasion of antidromic impulses into the M cell was suppressed during the EHP, but not during the collateral IPSP. Conductance increase during the IPSP did not interfere with the invasion of antidromic impulses.
Equilibrium and Ion Exchange Characteristics of Potassium and Sodium Accumulation by Barley Roots
Authors: Jackson P. C. , Stief K. J.
Published: May 2004

Potassium ion and Na+ influx and efflux rates into and from excised barley roots are compared with the maximum capacity of accumulation. Potassium ion and Na+ influx and efflux involve a cation exchange that is independent of simultaneous exchange of the accompanying anion. These exchange fluxes depend on the concentration and cation composition of the solutions from which they originate. Selective differences between K+ and Na+ fluxes are sufficient to account for a cationic distribution within the roots that differs markedly from that of the external solution and that persists for extended time periods. The accumulation maximum is a cation exchange equilibrium with the cation influx and efflux rates approaching equality. The equilibrium level is independent of the individual cation fluxes and the external solution concentration. It is a finite quantity which appears to be determined by the internal anion concentration including accumulated as well as endogenous anions.
Isolation of Relaxing Particles from Rat Skeletal Muscles in Zonal Centrifuges
Authors: Schuel H. , Lorand L. , Schuel R. , Anderson N. G.
Published: May 2004

Supernatants of rat skeletal muscle homogenates were fractionated by differential centrifugation and by zonal centrifugation in sucrose density gradients. Cytochrome oxidase was employed as an enzymatic marker for locating mitochondria. The subcellular fractions were also assayed for their ability to prevent the ATP-induced contraction of myofibrils. Both the mitochondrial and microsomal fractions obtained by differential fractionation were found to be rich in such relaxing activity, and the microsomal fraction was appreciably contaminated by mitochondria. In contrast to this, when fractionation was carried out by means of zonal centrifugation (4200 RPM x 205 min. to 40,000 RPM x 60 min.), relaxing activity was found to be associated only with particles having the sedimentation characteristics of microsomes (s20,w estimated to be between 370 and 1880S). Relaxing activity was not detected in the regions of the gradient containing either the starting sample zone (soluble phase) or the mitochondrial peak. The microsomal relaxing particles showed negligible cytochrome oxidase activity.
Cat Heart Muscle in Vitro
Authors: Page Ernest , Storm S. R.
Published: May 2004

The cells of cat right ventricular papillary muscles were depleted of K and caused to accumulate Na and water by preincubation at 2–3°C. The time courses of changes in cellular ion content and volume and of the resting membrane potential (Vm) were then followed after abrupt rewarming to 27–28°C. At physiological external K concentration ([K]o = 5.32 mM) recovery of cellular ion and water contents was complete within 30 minutes, the maximal observable rates of K uptake and Na extrusion (Δmmol cell ion/(kg dry weight) (min.)) being 3.4 and 3.6, respectively. The recovery rate was markedly slowed at [K]o = 1.0 mM. Rewarming caused Vm measured in cells at the muscle surface to recover within from <1 to 9 minutes, but only slight restoration of cellular ion contents (measured in whole muscles) had occurred after 10 minutes. Studies of recovery in NaCl-free sucrose Ringer's solution made it possible to separate the ouabain-insensitive outward diffusion of Na as a salt from a simultaneous ouabain-sensitive Na extrusion which is associated with a net cellular K uptake. A hypothesis consistent with these observations is that rewarming may activate a ouabain-sensitive "electrogenic" mechanism, most probably the net active transport of Na out of the cell, from which net K uptake may then follow passively.
K Fluxes in Frog Skin
Authors: Curran Peter F. , Cereijido Marcelino
Published: May 2004

A method has been developed for measuring K influx into the epithelial cells of frog skin from the inside solution. Diffusion delay in the connective tissue has been taken into account. Ninety-four per cent of skin K was found to exchange with K42 in the inside solution with a single time constant. K influx showed saturation with increasing K concentration, was not altered by imposing a potential difference of ±200 mv across the skin, and was inhibited by dinitrophenol, fluoroacetate, and ouabain. Relatively low concentrations of dinitrophenol (5 x 10-5 M) and fluoroacetate (10-10 M) had no effect on k influx but caused a 40 per cent decrease in net Na flux. There was no correlation between the rate of K uptake at the "inner barrier" and the rate of net Na transport. Reduction of net Na transport by lowering Na concentration in the outside solution caused little change in K uptake. These observations indicate that there is not a significant Na-K exchange involved in active transport of Na across the skin. K influx was found, however, to require Na in the inside bathing solution.
Diffusivity Measurements of Human Methemoglobin
Authors: Keller K. H. , Friedlander S. K.
Published: May 2004

Experimental measurements of the diffusion coefficient of human methemoglobin were made at 25°C with a modified Stokes diaphragm diffusion cell. A Millipore filter was used in place of the ordinary fritted disc to facilitate rapid achievement of steady state in the diaphragm. Methemoglobin concentrations varied from approximately 5 g/100 ml to 30 g/100 ml. The diffusion coefficient in this range decreased from 7.5 x 10-7 cm2/sec to 1.6 x 10-7 cm2/sec.
Ionic Interconversion of Pacemaker and Nonpacemaker Cultured Chick Heart Cells
Authors: Sperelakis Nick , Lehmkuhl D.
Published: May 2004

Trypsin-dispersed cells from hearts (ventricles) of 7 to 8 day chick embryos were cultured 3 to 21 days. The cells became attached to the culture dish and assembled into monolayer communities. By means of a bridge circuit, one microelectrode was used for simultaneously passing current and recording membrane potentials (Vm). The input resistance, calculated by the measured ΔVm for a known step of current, averaged 10 MΩ. Electrotonic depolarization of nonpacemaker cells had no effect on frequency of firing. Within 2 min after addition of Ba++ (5 to 10 mM) to the Tyrode bath, the cells became partially depolarized and quiescent nonpacemaker cells developed oscillations in Vm which led to action potentials. With time, the depolarization became nearly complete and the input resistance increased 2 to 10 times. During such sustained depolarizations, action potentials were no longer produced and often tiny oscillations were observed; however, large action potentials developed during hyperpolarizing pulses. Thus, the automaticity of the depolarized cell became apparent during artificial repolarization. Sr++ (5 to 10 mM) initially produced hyperpolarization and induced automaticity in quiescent nonpacemaker cells. Elevated [K+]o (20 to 30 mM) suppressed automaticity of pacemaker cells and decreased Rm concomitantly. Thus, Ba++ probably converts nonpacemaker cells into pacemaker cells independently of its depolarizing action. Ba++ may induce automaticity and depolarization by decreasing gK, and elevated [K+]o may depress automaticity by increasing gK. The data support the hypothesis that the level of gK determines whether a cell shall function as a pacemaker.
The Enzymatic Phosphorylation of Nucleic Acids and Its Application to End-Group Analysis
Authors: Richardson Charles C. , Weiss Bernard
Published: May 2004

Polynucleotide kinase catalyzes the transfer of a phosphate group from ATP to the 5'-hydroxyl termini of polynucleotides. Selective labeling of the 5'-hydroxyl termini of DNA with polynucleotide kinase has been used to study the number and the identity of the 5'-terminal residues of bacteriophage DNA's, and to examine the nature of the phosphodiester bond cleavages produced by endonucleases and by sonic irradiation. The intact strands of T7 DNA bear 5'-phosphoryl end-groups; only deoxyadenylate and deoxythymidylate are present as 5'-terminal residues. The intact strands of native λ-DNA bear 5'-hydroxyl end-groups. M13 DNA, a circular molecule, cannot be phosphorylated. End-group labeling of DNA provides a method for determination of molecular weight; calibration against other DNA preparations is not required. The molecular weight of a single strand of T7 DNA, determined by end-group labeling, is 13.1 x 106; the molecular weight of a single strand of λ-DNA is 16.0 x 106. These values are in agreement with molecular weight estimates by sedimentation analysis and electron microscopy. Sonic irradiation of DNA has been shown to favor the production of polynucleotides terminated by 5'-phosphomonoester groups. All four deoxyribonucleotides are present as 5'-terminal residues of sonicated DNA.
The ß-Glucosidase of the Yeast Cell Surface
Authors: Kaplan J. Gordin , Tacreiter Wanda
Published: May 2004

There are two distinct components of the system which limits the rate at which intact cells of S. cerevisiae C hydrolyze external ß-glucosides; one component requires metabolic energy and the other is stereospecific for ß-glucosides. The stereospecific component is localized at the cell membrane, as shown by its sensitivity to heavy metal inhibitors which did not penetrate the cell under the conditions used. It was shown that cellobiose-grown cells were able to remove cellobiose from the medium in which they were incubated, and that the cellobiose uptake system was identical to that which limits the patent ß-glucosidase activity. In order to test the hypothesis that the system in question was a transport system, for ß-glucosides the ability of cellobiose-grown cells to take up 14C-labeled methyl-ß-glucoside (MBG) was studied. The induced cells were able to take up MBG-14C and the label could be partially chased out by cold MBG and cellobiose; glucose-grown cells could not incorporate label. However, induced cells could not take up label when incubated with 14C-MBG, thus excluding the hypothesis of transport of intact ß-glucosides. It was concluded that the stereospecific membrane component was actually a ß-glucosidase, coupled to an energy-dependent transport system for the glucose moiety; the function of the latter was rate-limiting in the over-all activity of the entire system.
Effect of Specific Antibodies on the Excitability of Internally Perfused Squid Axons
Authors: Huneeus F. C. , Fernandez H. L.
Published: May 2004

Giant axons from the squid Dosidicus gigas were internally perfused with rabbit antiaxoplasm antibodies and their effect upon the action potential and the membrane potential was studied. Necessary requirements for the antibodies to affect these parameters in a consistent manner were: (a) removal of the bulk of axoplasm from the perfused zone, accomplished by initially perfusing with a cysteine-rich (400 mM) solution, and (b) addition of small amounts of cysteine (30 mM) to the antibody-containing solution. When these experimental conditions were met, conduction block ensued generally within 3 hr of the first contact of the axon inner surface with the antibody Antineurofilament antibodies and nonspecific antibodies had no effect. External application of antiaxoplasm antibodies had no effect.
Active State in Heart Muscle
Authors: Sonnenblick Edmund H.
Published: May 2004

The course of active state in heart muscle has been analyzed using a modified quick release method. The onset of maximum active state was found to be delayed, requiring 110–500 msec from time of stimulation, while the time to peak isometric tension required 250–650 msec. Further, the time from stimulation to peak tension was linearly related to the time required to establish maximum intensity of active state as well as to the duration of maximum active state. The duration of maximum active state was prolonged (90–220 msec), occupying most of the latter half of the rising phase of the isometric contraction. Norepinephrine (10-5 M) shortened the latency from electrical stimulus to mechanical response, accelerated the onset of maximum active state, increased its intensity, decreased its duration, and accelerated its rate of decline. These changes were accompanied by an increase in the rate of tension development and the tension developed while the time from stimulation to peak isometric tension was abbreviated. Similar findings were shown for strophanthidin (1 µg/ml) although lesser decrements in the duration of maximum active state and time to peak tension were found than with norepinephrine for similar increments in the maximum intensity of active state.
The Mechanochemistry of Cardiac Muscle
Authors: Pool Peter E. , Sonnenblick Edmund H.
Published: May 2004

The utilization of creatine phosphate (CP) and adenosine triphosphate (ATP) was studied in the iodoacetate (IAA) and nitrogen (N2)-treated cat papillary muscle. Under these conditions the net production of ATP does not occur, and the net utilization of ATP is reflected in a fall in CP concentration. The rate of energy utilization of the IAA-N2-treated cat papillary muscle resting without tension was 0.68 µmole CP/g/min. This rate was increased to 1.07 µmole/g/min when muscles were passively stretched with 2 g of tension. In a series of isometrically contracting muscles CP utilization was found to be proportional to the number of activations and the summated contractile element work. These rates of CP utilization were 0.083 µmole/g/activation and 0.0059 µmole/g-cm of work. The calculated mechanochemical coupling efficiency was 33%.
Cation Interdiffusion in Squid Giant Axons
Authors: Tasaki Ichiji , Singer Irwin , Watanabe Akira
Published: May 2004

Radiotracer techniques were used to study the influxes and effluxes of various univalent cations in internally perfused squid giant axons. Membrane currents and conductances were determined by the voltage-clamp technique under analogous internal and external conditions. Both sodium-containing and sodium-free internal and external media were studied. Membrane impedance was measured with an ac impedance bridge to determine the general magnitude and time course of the impedance loss which accompanied the excitation process in both varieties of external media. Maximum transmembrane currents were found to be of comparable magnitude to the charge transfer associated with the peak interdiffusion flux measured under the same conditions. The product of the membrane resistance and the interdiffusion flux remained constant over a wide range of resistance and flux values, both at rest and during activity, both in sodium-containing and sodium-free media. The implications of these findings for excitation theory are discussed.
The Selective Inhibition of Delayed Potassium Currents in Nerve by Tetraethylammonium Ion
Authors: Hille Bertil
Published: May 2004

The effect of tetraethylammonium ion (TEA) on the voltage clamp currents of nodes of Ranvier of frog myelinated nerve fibers is studied. The delayed K currents can be totally abolished by TEA without affecting the transient Na currents or the leakage current in any way. Both inward and outward currents disappear. In low TEA concentrations small K currents remain with normal time constants. The dose-response relationship suggests the formation of a complex between TEA and a receptor with a dissociation constant of 0.4 mM. Other symmetrical quaternary ammonium ions have very little effect. There is no competition between TEA and agents that affect the Na currents such as Xylocaine, tetrodotoxin, or Ca ions. The pharmacological data demonstrate that the Na, K, and leakage permeabilities are chemically independent, probably because their mechanisms occupy different sites on the nodal membrane. The data are gathered and analyzed by digital computer.
Reactivities of Actin as a Contractile Protein
Authors: Hayashi Teru
Published: May 2004

The molecular basis for the mechanism of contraction in striated muscle, with primary emphasis on the interaction between the thick and thin filaments and the role of the thin (actin) filaments, is the theme presented. Recent information relating to actin-myosin interaction points up the fact that definitive statements cannot be made regarding the molecular interaction(s) that lead to contraction. Nevertheless, the properties of actin indicate that (a) actin in the monomeric state has properties differing markedly from actin in the polymer (filament) state; (b) these property differences may be significant in the contractile process, for they include changes in the reactivity of the bound nucleotide and actin-myosin complex formation; (c) the bound nucleotide seems to be required in the contraction process. For these, and other, reasons discussed, the tentative hypothesis is advanced that the contraction reaction involves local changes in the actin filament providing local monomer or monomer-like actin units in the reaction with myosin.
Removal of Potassium Negative Resistance in Perfused Squid Giant Axons
Authors: Lecar Harold , Ehrenstein Gerald , Binstock Leonard , Taylor Robert E.
Published: May 2004

Squid giant axons, internally and externally perfused with solutions having potassium as the only cation, exhibit an approximately linear steady-state current-voltage relation. When small amounts of calcium and magnesium are present in the external potassium solution, the current-voltage curve is markedly nonlinear, exhibiting the rectification and negative resistance which have been observed for intact axons in isosmotic potassium solutions. The effects of perfusion and removal of external divalent cations are interpreted in terms of two components of current, a linear component and a nonlinear time-varying component. The former is increased and the latter diminished by the removal of the external divalent cations.
Water Permeability of Thin Lipid Membranes
Authors: Cass Albert , Finkelstein Alan
Published: May 2004

The osmotic permeability coefficient, Pf, and the tagged water permeability coefficient, Pd, were determined for thin (<100 A) lipid membranes formed from ox brain lipids plus DL-α-tocopherol; their value of approximately 1 x 10-3 cm/sec is within the range reported for plasma membranes. It was established that Pf = Pd. Other reports that Pf > Pd can be attributed to the presence of unstirred layers in the experimental determination of Pd. Thus, there is no evidence for the existence of aqueous pores in these thin phospholipid membranes. The adsorption onto the membrane of a protein that lowers its electrical resistance by a factor of 103 was found not to affect its water permeability; however, glucose and sucrose were found to interact with the membrane to modify Pf. Possible mechanisms of water transport across these films are discussed, together with the implications of data obtained on these structures for plasma membranes.
Regulation of Cardiac Muscle Contractility
Authors: Katz Arnold M.
Published: May 2004

The heart's physiological performance, unlike that of skeletal muscle, is regulated primarily by variations in the contractile force developed by the individual myocardial fibers. In an attempt to identify the basis for the characteristic properties of myocardial contraction, the individual cardiac contractile proteins and their behavior in contractile models in vitro have been examined. The low shortening velocity of heart muscle appears to reflect the weak ATPase activity of cardiac myosin, but this enzymatic activity probably does not determine active state intensity. Quantification of the effects of Ca++ upon cardiac actomyosin supports the view that myocardial contractility can be modified by changes in the amount of calcium released during excitation-contraction coupling. Exchange of intracellular K+ with Na+ derived from the extracellular space also could enhance myocardial contractility directly, as highly purified cardiac actomyosin is stimulated when K+ is replaced by an equimolar amount of Na+. On the other hand, cardiac glycosides and catecholamines, agents which greatly increase the contractility of the intact heart, were found to be without significant actions upon highly purified reconstituted cardiac actomyosin.
Ion Fluxes and Short-Circuit Current in Internally Perfused Cells of Valonia ventricosa
Authors: Gutknecht John
Published: May 2004

Ion transport in the giant celled marine alga, Valonia ventricosa, was studied during internal perfusion and short-circuiting of the vacuole potential. The perfusing and bathing solutions were similar to natural Valonia sap and contained the following concentrations of major ions: Na 51, K 618, and Cl 652 mM. The average short-circuit current (Isc) was 97 pEq/cm2 sec (inward positive current), and the average open-circuit potential difference (PD) was 74 mv (vacuole positive to external solution). Perfused and short-circuited cells showed a small net influx of Na (2.0 pEq/cm2 sec) and large net influxes of K (80 pEq/cm2 sec) and Cl (50 pEq/cm2 sec). Unidirectional K influx was proportional to Isc, but more than one-half of the Isc remained unaccounted for. Both the Isc and PD were partly light-dependent, declining rapidly during the first 1–2 min of darkness. Ouabain (5 x 10-4 M) had little effect on the influx of Na or K and had no effect on Iinf or PD. Fluid was absorbed at a rate of about 93 pliter/cm2 sec. Reversing the direction of fluid movement by adding mannitol to the outside solution had little effect on ion movements. The ionic and electrical properties of normal and perfused cells of Valonia are compared.
Quinine and Caffeine Effects on 45Ca Movements in Frog Sartorius Muscle
Authors: Isaacson Allen , Sandow Alexander
Published: May 2004

1 mM caffeine, which produces only twitch potentiation and not contracture in frog sartorius muscle, increases both the uptake and release of 45Ca in this muscle by about 50 %, thus acting like higher, contracture-producing concentrations but less intensely. Quinine increases the rate of release of 45Ca from frog sartorius but not from the Achilles tendon. The thresholds for the quinine effect on 45Ca release and contracture tension are about 0.1 and 0.5 mM, respectively, at pH 7.1. Quinine (2 mM) also doubles the uptake of 45Ca by normally polarized muscle. However, there are variable effects of quinine upon 45Ca uptake in potassium-depolarized muscle. Quinine (2 mM), increases the Ca, Na, and water content of muscle while decreasing the K content. Both caffeine (1 mM) and quinine (2 mM) act to release 45Ca from muscles that have been washed in Ringer's solution from which Ca was omitted and to which EDTA (5 mM) was added. These results, correlated with those of others, indicate that a basic effect of caffeine and quinine on muscle is to directly release activator Ca2+ from the sarcoplasmic reticulum in proportion to the drug concentration. The drugs may also enhance the depolarization-induced Ca release caused by extra K+ or an action potential. In respect to the myoplasmic Ca2+ released by direct action of the drugs, a relatively high concentration is required to activate even only threshold contracture, but a much lower concentration, added to that released during excitation-contraction coupling, is associated with the condition causing considerable twitch potentiation.
The Wave Form of Luminescence Emitted by Noctiluca
Authors: Eckert Roger
Published: May 2004

The wave shape, intensity, and time course of the flash were examined with the aid of electronic operations in order to characterize the luminescence response and examine the in vivo dynamics of the light reaction. The most prominent single component of the flash shape is its exponential decay, beginning several milliseconds after the intensity maximum, with a mean rate constant at 23°C of -0.088 msec-1. Earlier components of the flash curve are more complex, exhibiting no pure exponentials with time. As predicted from previous observations, the time course of the flash triggered by a propagated action potential, and therefore influenced by the conduction time of the triggering potential, is measurably slower than that of the synchronously triggered flash. The time course of emission from individual specimens is otherwise quite stable, undergoing only limited slowing with short-interval fatigue or specimen deterioration in spite of marked changes in the amplitude of the wave form. Relative stability of amplitude is obtained when flashes are elicited at regular intervals greater than 10 sec. On the basis of an analogue computer simulation (Appendix) the dynamics of the luminescence wave shape were found to be compatible with a short sequence of first order processes acting on an initial brief transient.
Pharmacological Modifications of the Sodium Channels of Frog Nerve
Authors: Hille Bertil
Published: May 2004

Voltage clamp measurements on myelinated nerve fibers show that tetrodotoxin, saxitoxin, and DDT specifically affect the sodium channels of the membrane. Tetrodotoxin and saxitoxin render the sodium channels impermeable to Na ions and to Li ions and probably prevent the opening of individual sodium channels when one toxin molecule binds to a channel. The apparent dissociation constant of the inhibitory complex is about 1 nM for the cationic forms of both toxins. The zwitter ionic forms are much less potent. On the other hand, DDT causes a fraction of the sodium channels that open during a depolarization to remain open for a longer time than is normal. The effect cannot be described as a specific change in sodium inactivation or as a specific change in sodium activation, for both processes continue to govern the opening of the sodium channels and neither process is able to close the channels. The effects of DDT are very similar to those of veratrine.
Concentrative Accumulation of Choline by Human Erythrocytes
Authors: Martin K.
Published: May 2004

Influx and efflux of choline in human erythrocytes were studied using 14C-choline. When incubated at 37°C with physiological concentrations of choline erythrocytes concentrate choline; the steady-state ratio is 2.08 ± 0.23 when the external choline is 2.5 µM and falls to 0.94 ± 0.13 as the external concentration is raised to 50 µM. During the steady state the influx of choline is consistent with a carrier system with an apparent Michaelis constant of 30 x 10-6 and a maximum flux of 1.1 µmoles per liter cells per min. For the influx into cells preequilibrated with a choline-free buffer the apparent Michaelis constant is about 6.5 x 10-6 M and the maximum flux is 0.22 µmole per liter cells per min. At intracellular concentrations below 50 µmole per liter cells the efflux in the steady state approximates first order kinetics; however, it is not flux through a leak because it is inhibited by hemicholinium. Influx and efflux show a pronounced exchange flux phenomenon. The ability to concentrate choline is lost when external sodium is replaced by lithium or potassium. However, the uphill movement of choline is probably not coupled directly to the Na+ electrochemical gradient.
Strophanthidin-Sensitive Components of Potassium and Sodium Movements in Skeletal Muscle As Influenced by the Internal Sodium Concentration
Authors: Sjodin R. A. , Beaugé L. A.
Published: May 2004

"Low sodium" muscles were prepared which contained around 5 mmoles/kg fiber of intracellular sodium. "High sodium" muscles containing between 15 and 30 mmoles/kg fiber of intracellular sodium were also prepared. In low sodium muscles application of 10-5 M strophanthidin reduced potassium influx by about 5%. Potassium efflux was unaffected by strophanthidin under these conditions. In high sodium muscles, 10-5 M strophanthidin reduced potassium influx by 45% and increased potassium efflux by 70%, on the average. In low sodium muscles sodium efflux was reduced by 25% during application of 10-5 M strophanthidin while in high sodium muscles similarly treated, sodium efflux was reduced by about 60%. Low sodium muscles showed a large reduction in sodium efflux when sodium ions in the Ringer solution were replaced by lithium ions. The average reduction in sodium efflux was 4.5-fold. Of the amount of sodium efflux remaining in lithium. Ringer's solution, 40% could be inhibited by application of 10-5 M strophanthidin. The total sodium efflux from low sodium muscles exposed to Ringer's solution in which lithium had been substituted for sodium ions for a period of 1 hr can be fractionated as 78% Na-for-Na interchange, 10% strophanthidin-sensitive sodium pump, and 12% residual sodium efflux. It is concluded that large strophanthidin-sensitive components of sodium and potassium flux can be expected only at elevated sodium concentrations within the muscle cells.
The Effect of Calcium Depletion upon the Tension-Independent Component of Cardiac Heat Production
Authors: Gibbs C. L. , Vaughan P.
Published: May 2004

Rabbit papillary muscle has been exposed to calcium concentrations ranging from 2.5 mM to zero. Its mechanical and electrical activity has been monitored and its heat production measured using a myothermic technique. Calcium depletion decreased the magnitude of the tension-independent heat per contraction from a mean of 0.45 mcal/g muscle to 0.31 mcal/g muscle at room temperature (18° to 22°C). Calcium-chelating agents did not abolish action potential conduction under the experimental conditions used but they further reduced the magnitude of the tension-independent heat. Raising the temperature from room level to 32°C decreased the tension-independent heat from a mean of 0.52 to a mean of 0.24 mcal/g muscle. Calcium depletion at 32°C further decreased this heat and it was calculated that the energy now liberated in activating the muscle was about 2% of the total energy normally liberated in the working heart. The results are interpreted in terms of current biochemical and myothermic data.
The Form of Sodium-Calcium Competition at the Frog Myoneural Junction
Authors: Birks R. I. , Burstyn P. G. R. , Firth D. R.
Published: May 2004

The times required for a steady rate of miniature end-plate potential discharge to be reached in response to changes in extracellular [K+], [Na+], and [Ca++] have been measured. In the presence of 15 mM KCl, Ca++ raises and Na+ lowers the steady-state mepp frequency; but the depressive effect on Na+ is not specific: Li+ can replace Na+ to a large extent. Mepp frequency has been found to depend on the ratio of [Cao++]/[Nao+]. It is assumed that in the steady state, intracellular sodium will change when extracellular sodium is changed. Because both intracellular and extracellular sodium at motor nerve endings affect acetylcholine release, it is proposed that mepp frequency depends on the ratio [Cao] [Nai]2·/[Nao]2 Two models are proposed. Firstly, to account for the action of sodium and calcium a carrier is postulated for which Ca++ and Na+ compete. The carrier determines a maximum level of intracellular Ca++ far lower than predicted by the Nernst equation for Ca. Secondly, to account for activation of acetylcholine release by a small influx of Ca++, the ions are presumed to enter the nerve ending in a two stage process through a small intermediate compartment and to act on the acetylcholine release site in this region rather than after entering directly into the cell.
Current- and Voltage-Clamped Studies on Myxicola Giant Axons
Authors: Binstock L. , Goldman L.
Published: May 2004

A new dissection procedure for preparing Myxicola giant axons for observation under voltage clamp is described. Preparation time is generally 40–45 min. 65–70% of the preparations attempted may be brought through the entire procedure, including insertion of the long internal electrode, and support an initial action potential amplitude of 100 mv or greater. Mean values for axon diameter, resting membrane potential, action potential amplitude, maximum peak inward transient current, and resting membrane resistance are 560 µ, —66.5 mv, 112 mv, 0.87 ma/cm2 and 1.22 KΩ cm 2 respectively. Cut branches do not seem to be a problem in this preparation. Behavior under voltage clamp is reasonably stable over several hours. Reductions in maximum inward transient current of 10% and in steady-state current of 5–10% are expected in the absence of any particular treatment. Tetrodotoxin blocks the action potential and both the inward and outward transient current, but has no effect on either the resting membrane potential or the steady-state current. This selective action of tetrodotoxin on the transient current is taken as an indication that this current component is probably carried by Na.
Current Separations in Myxicola Giant Axons
Authors: Goldman L. , Binstock L.
Published: May 2004

The effect of reducing the external sodium concentration, [Na]o, on resting potential, action potential, membrane current, and transient current reversal potential in Myxicola giant axons was studied. Tris chloride was used as a substitute for NaCl. Preliminary experiments were carried out to insure that the effect of Tris substitution could be attributed entirely to the reduction in [Na]o. Both choline and tetramethylammonium chloride were found to have additional effects on the membrane. The transient current is carried largely by Na, while the delayed current seems to be independent of [Na]o. Transient current reversal potential behaves much like a pure Nernst equilibrium potential for sodium. Small deviations from this behavior are consistent with the possibility of some small nonsodium component in the transient current. An exact PNa/PK for the transient current channels could not be computed from these data, but is certainly well greater than unity and possibly quite large. The peak of the action potential varied with [Na]o as expected for a sodium action potential with some substantial potassium permeability at the time of peak. Resting membrane potential is independent of [Na]o. This finding is inconsistent with the view that the resting membrane potential is determined only by the distribution of K and Na, and PNa/PK. It is suggested that PNa/PK's obtained from resting membrane potential-potassium concentration data do not always have the physical meaning generally attributed to them.
The Nature of the Negative Resistance in Bimolecular Lipid Membranes Containing Excitability-Inducing Material
Authors: Ehrenstein Gerald , Lecar Harold , Nossal Ralph
Published: May 2004

When sufficiently small amounts of excitability-inducing material (EIM) are added to a bimolecular lipid membrane, the conductance is limited to a few discrete levels and changes abruptly from one level to another. From our study of these fluctuations, we have concluded that the EIM-doped bilayer contains ion-conducting channels capable of undergoing transitions between two states of different conductance. The difference in current between the "open" and "closed" states is directly proportional to the applied membrane potential, and corresponds to a conductance of about 3 x 10-10 ohm-1. The fraction of the total number of channels that is open varies from unity to zero as a function of potential. The voltage-dependent opening and closing of channels explains the negative resistance observed for bimolecular lipid membranes treated with greater amounts of EIM.
The Sodium-Alanine Interaction in Rabbit Ileum
Authors: Curran Peter F. , Hajjar Jean Jacques , Glynn I. M.
Published: May 2004

The interaction between Na transfer and alanine transfer across the mucosal border of rabbit ileum has been studied further by examining the effect of alanine on Na movement. Studies on strips of mucosa treated with ouabain showed that net Na movements against a Na concentration difference could be caused by a concentration difference of alanine. Na extrusion from mucosal cells was demonstrated when cellular alanine concentration exceeded that in the external medium. Conversely, the cells took up Na against a concentration difference when external alanine concentration was greater than cellular concentration. Unidirectional Na efflux from the cells toward the mucosal solution was increased by loading the cells with alanine. The relation between the increment in Na efflux and alanine efflux was approximately that predicted by the model of Curran et al. (reference 2) for the Na-alanine interaction at the mucosal border of the cells. The results offer further indication that the transport system is reversible and symmetrical.
Molecular Aspects of Polyene- and Sterol-Dependent Pore Formation in Thin Lipid Membranes
Authors: Dennis Vincent W. , Stead Nancy W. , Andreoli Thomas E.
Published: May 2004

Amphotericin B modifies the permeability properties of thin lipid membranes formed from solutions containing sheep red cell phospholipids and cholesterol. At 10-6 M amphotericin B, the DC membrane resistance fell from ≈108 to ≈102 ohm-cm2, and the membranes became Cl--, rather than Na+-selective; the permeability coefficients for hydrophilic nonelectrolytes increased in inverse relationship to solute size, and the rate of water flow during osmosis increased 30-fold. These changes may be rationalized by assuming that the interaction of amphotericin B with membrane-bound sterol resulted in the formation of aqueous pores. N-acetylamphotericin B and the methyl ester of N-acetylamphotericin B, but not the smaller ring compounds, filipin, rimocidin, and PA-166, produced comparable permeability changes in identical membranes, and amphotericin B and its derivatives produced similar changes in the properties of membranes formed from phospholipid-free sterol solutions. However, amphotericin B did not affect ionic selectivity or water and nonelectrolyte permeability in membranes formed from solutions containing phospholipids and no added cholesterol, or when cholesterol was replaced by either cholesterol palmitate, dihydrotachysterol, epicholesterol, or Δ5-cholesten-3-one. Phospholipid-free sterol membranes exposed to amphotericin B or its derivatives were anion-selective, but the degree of Cl- selectivity varied among the compounds, and with the aqueous pH. The data are discussed with regard to, first, the nature of the polyene-sterol interactions which result in pore formation, and second, the functional groups on amphotericin B responsible for membrane anion selectivity.
Kinetics of Excitable Membranes
Authors: Offner Franklin F.
Published: May 2004

An understanding of the properties of excitable membranes requires the calculation of ion flow through the membrane, including the effects of nonuniformity in the transverse membrane properties (mobilities, fixed charge, electric field). Permeability is apparently controlled at the external interface. Two factors may be involved here: the statistical blocking of pores by divalent cations, and activation energy. Only the former is included in the present treatment. When the total transmembrane voltage is varied, a redistribution in ionic concentration occurs. This can cause a change in boundary (zeta) potential, large in comparison with the applied voltage change—"voltage amplification." The result is a steep change in membrane conductance. The calculated flow curves are compared with experimental results. The Appendix gives an outline of the numerical method used for solving the boundary value problem with several diffusible ions, across a nonuniform regime.
The Cellular Transport of Magnesium in Rat Liver
Authors: Wallach S. , Gamponia P. J. , Ahmed S. A.
Published: May 2004

The bidirectional transport of Mg in rat liver was studied using slices labeled with 28Mg in a closed two-compartment system under steady-state conditions. The influx (Kbs) and efflux (Ksb) transfer coefficients governing transport between the extracellular phase and a rapidly exchanging cell fraction were 0.074 and 0.019 per min, respectively. An increased extracellular concentration of Mg++ caused a 30% decrease in Kbs and a 31% increase in Ksb. A decreased extracellular Mg++ had an opposite effect. At 0°C, both transfer coefficients were reduced by 65%. Increased pH and NaCN increased transport, whereas Ca++ reduced transport. Reduced pH, altered Na+:K+ ratio, Sr++, glucose deletion, iodoacetate, ethanol, and lactate had no significant influence. Dinitrophenol reduced Ksb but had no effect on Kbs. These data support the thesis that the intracellular concentration of Mg is in part regulated by a reciprocal change in the influx transfer coefficient and a parallel change in the efflux transfer coefficient in response to altered extracellular concentrations of Mg++. The qualitative and quantitative similarities of Mg and Ca transport in this system suggest that Mg and Ca share a common transport mechanism which is primarily dependent upon the binding of these divalent cations to macromolecular ligands within the cell membrane or within the cell.