bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of K Inactivation and TEA Action in the Supramedullary Cells of Puffer
Authors: Nakajima Shigehiro
Published: May 2004

Under the voltage clamp condition, the K inactivation was analyzed in cells bathed in the isosmotic KCl Lophius-Ringer solution. After conditioning hyperpolarization, the cells respond to depolarizations with increased K permeability, which in turn is decreased during maintained depolarizations. The steady-state levels of the K inactivation as a function of the membrane potential are related by an S-shaped curve similar to that which describes the steady-state Na inactivation in the squid giant axon. TEA reduced the K conductance by a factor which is independent of the potential, and without a shift of the inactivation curve along the voltage axis. The rapid phase of the K activation is less susceptible to TEA than the slow phase of the K activation. Hyperpolarizing steps remove the K inactivation, the rate of the removal being faster the larger the hyperpolarization from the standard potential of about -60 mv.
The Relation between Salt and Ionic Transport Coefficients
Authors: Kedem Ora , Leaf Alexander
Published: May 2004

The reflection coefficient was originally introduced by Staverman to describe the movement of nonelectrolytes through membranes. When this coefficient is extended to salts, one has a choice of defining this term for the whole salt moving as a single electrically neutral component or for the individual ions of the salt. The latter definition is meaningful only in the absence of an electric field across the permeability barrier. This condition may be achieved with the voltage clamp or short-circuit technique and is especially useful in dealing with biological systems in which one rarely has only a single salt or even equal concentrations of the major anion and cation. The relations between the transport coefficients for the salt and its individual ions are derived. The special conditions which may result in negative osmosis through a charged membrane in the presence of a salt are discussed.
Differences in Na and Ca Spikes As Examined by Application of Tetrodotoxin, Procaine, and Manganese Ions
Authors: Hagiwara Susumu , Nakajima Shigehiro
Published: May 2004

The effects of tetrodotoxin, procaine, and manganese ions were examined on the Ca spike of the barnacle muscle fiber injected with Ca-binding agent as well as on the action potential of the ventricular muscle fiber of the frog heart. Although tetrodotoxin and procaine very effectively suppress the "Na spike" of other tissues, no suppressing effects are found on "Ca spike" of the barnacle fiber, while the initiation of the Ca spike is competitively inhibited by manganese ions. The initial rate of rise of the ventricular action potential is suppressed by tetrodotoxin and procaine but the plateau phase of the action potential is little affected. In contrast the suppressing effect of manganese ions is mainly on the plateau phase. The results suggest that the plateau phase of the ventricular action potential is related to the conductance increase in the membrane to Ca ions even though Na conductance change may also contribute to the plateau.
Electrical Characteristics of Triturus Egg Cells during Cleavage
Authors: Ito Shizuo , Hori Nobuaki
Published: May 2004

The membrane potential in the blastomeres of dividing Triturus egg cells increases progressively from the first cleavage to the late morula stages. Both the animal and vegetal poles show the same increasing trend in potential; there is no significant potential difference between them. Upon first cell cleavage, the total resistance of the egg cell surface in contact with the exterior decreases to about one-tenth of its value before cleavage, and then remains rather constant up to the late morula stage. The specific resistance of this membrane surface drops rather abruptly upon first cleavage, and rises progressively during the morula stage. The resistance of the junctional membrane surface of the blastomeres, that is, the membrane formed at the former planes of cleavage, is small in relation to that of the cell surface in contact with the exterior. As a result, the blastomeres are electrically coupled throughout all stages of embryonic development examined.
Active Transport of D-Xylose in the Isolated Small Intestine of the Bullfrog
Authors: Lassen Ulrik V. , Csáky T. Z.
Published: May 2004

Fluxes of D-xylose-1-C14 (xylose) across the wall of the isolated intestine of the bullfrog were studied. When sodium was the principal cation in the mucosal bathing fluid, the transport rate of xylose from the mucosa to the serosa was about 5 times greater than the transport rate from the serosa to the mucosa, indicating an active intestinal transport for this sugar. With potassium as the principal cation on the mucosal side, the transport rate of xylose from the mucosal to the serosal compartment is reduced about 5 to 6 times without appreciable change in the serosal to mucosal transport. The asymmetry was also considerably reduced when ouabain was added to the mucosal and serosal compartments. The data confirm the in vitro and in vivo observations indicating active transport of xylose and are also in accord with the earlier findings that active transport of sugars in the intestine is dependent upon the presence of sodium ions in the mucosal compartment and is inhibited by cardioactive steroids. Since the chemical constitution of xylose does not meet the requirements which were hitherto considered necessary for active transport of sugars in the intestine, this structural requirement has to be revised.
Competitive Action of Calcium and Procaine on Lobster Axon
Authors: Blaustein Mordecai P. , Goldman David E.
Published: May 2004

Voltage clamp studies with the squid giant axon have shown that changes in the external calcium concentration (Frankenhaeuser and Hodgkin, 1957) shift the sodium and potassium conductance versus membrane potential curves along the potential axis. Taylor (1959) found that procaine acts primarily by reducing the sodium and, to a lesser extent, the potassium conductances. Both procaine and increased calcium also delay the turning on of the sodium conductance mechanism. Calcium and procaine have similar effects on lobster giant axon. In addition, we have observed that the magnitude of the response to procaine is influenced by the external calcium concentration. Increasing external calcium tends to reduce the effectiveness of procaine in decreasing sodium conductance. Conversely, procaine is more effective in reducing the membrane conductance if external calcium is decreased. The amplitude of the nerve action potential reflects these conductance changes in that, for example, reductions in amplitude resulting from the addition of procaine to the medium are partially restored by increasing external calcium, as was first noted by Aceves and Machne (1963). These phenomena suggest that calcium and procaine compete with one another with respect to their actions on the membrane conductance mechanism. The fact that procaine and its analogues compete with calcium for binding to phospholipids in vitro (Feinstein, 1964) suggests that the concept of competitive binding to phospholipids may provide a useful model for interpreting these data.
Amino Acid and Sugar Transport in Rabbit Ileum
Authors: Schultz Stanley G. , Fuisz Robert E. , Curran Peter F.
Published: May 2004

L-Alanine and 3-O-methyl-D-glucose accumulation by mucosal strips from rabbit ileum has been investigated with particular emphasis on the interaction between Na and these transport processes. L-Alanine is rapidly accumulated by mucosal tissue and intracellular concentrations of approximately 50 mM are reached within 30 min when extracellular L-alanine concentration is 5 mM. Evidence is presented that intracellular alanine exists in an unbound, osmotically active form and that accumulation is an active transport process. In the absence of extracellular Na, the final ratio of intracellular to extracellular L-alanine does not differ significantly from unity and the rate of net uptake is markedly inhibited. Amino acid accumulation is also inhibited by 5 x 10-5 M ouabain. 3-O-methyl-D-glucose accumulation by this preparation is similarly affected by ouabain and by incubation in a Na-free medium. The effects of amino acid accumulation, of ouabain, and of incubation in a Na-free medium on cell water content and intracellular Na and K concentrations have also been investigated. These results are discussed with reference to the two hypotheses which have been suggested to explain the interaction between Na and intestinal nonelectrolyte transport.
Topochemical Factors in Potentiation of Contraction by Heavy Metal Cations
Authors: Sandow Alexander , Isaacson Allen
Published: May 2004

In addition to the previously studied Zn2+, low concentrations (about 0.5 mM) of Be2+, Ba2+, Cd2+, Ni2+, Cu2+, Pt4+ and, outstandingly, 0.5 µM of UO22+, potentiate the twitch of frog sartorius and toe muscles by prolonging the active state of contraction. The degree of potentiation is a roughly S-shaped function of p(metal2+), suggesting that each metal binds to a ligand of the muscle fiber, representative apparent affinity constants being: UO22+, 5 x 106; Zn2+, 2.8 x 105; and Cd2+, 2 x 104. UO22+ potentiation effects are rapidly reversed by PO4, and Zn2+ and Cd2+ effects by EDTA, PO4, and cysteine. The rapidity of these reversals by the nonpenetrating EDTA and PO4, and the fact that heavy metal ions evidently potentiate by prolonging the action potential, indicate that the metal potentiators exert their primary action at readily accessible (i.e. plasma and T tubular) membrane sites. The relatively slow kinetics of development of potentiation, and the even slower reversal of it in pure Ringer's solution, indicate that the metal ions are bound to connective tissue, as well as to muscle fibers. The binding effects at the readily accessible membrane sites evidently impairs delayed rectification and thus modifies the action potential and excitation-contraction coupling so as to cause potentiation. SH is excluded, and PO4 and imidazole are possibilities, as the membrane ligand binding the potentiating metal ions.
The Effect of Calcium on the Desensitization of Membrane Receptors at the Neuromuscular Junction
Authors: Manthey Arthur A.
Published: May 2004

Desensitization, as represented by the progressive decline in the electromotive effects of depolarizing agents at the neuromuscular junction, was studied by observing the time course of changes in effective transmembrane resistance during the prolonged application of 0.27 mM carbamylcholine to the postjunctional region of frog skeletal muscle fibers. The effective transmembrane resistance was measured by means of two intracellular microelectrodes implanted in the junctional region of single muscle fibers. When carbamylcholine was applied to the muscle there was an immediate decrease in the effective membrane resistance followed by a slower return toward control values which was identified as the phase of desensitization. When the calcium concentration was increased from 0 to 10 mM there was an approximately sevenfold increase in the rate of desensitization. On the other hand, an increase in the concentration of sodium from 28 to 120 mM caused a slowing of the rate of desensitization. Even in muscles depolarized by potassium sulfate, calcium increased the rate of desensitization while high concentrations of potassium tended to prolong the process. Some mechanisms by which calcium might exert these effects are discussed.
Physical and Topological Properties of Circular DNA
Authors: Vinograd Jerome , Lebowitz' Jacob
Published: May 2004

Several types of circular DNA molecules are now known. These are classified as single-stranded rings, covalently closed duplex rings, and weakly bonded duplex rings containing an interruption in one or both strands. Single rings are exemplified by the viral DNA from ϕX174 bacteriophage. Duplex rings appear to exist in a twisted configuration in neutral salt solutions at room temperature. Examples of such molecules are the DNA's from the papova group of tumor viruses and certain intracellular forms of ϕX and λ-DNA. These DNA's have several common properties which derive from the topological requirement that the winding number in such molecules is invariant. They sediment abnormally rapidly in alkaline (denaturing) solvents because of the topological barrier to unwinding. For the same basic reason these DNA's are thermodynamically more stable than the strand separable DNA's in thermal and alkaline melting experiments. The introduction of one single strand scission has a profound effect on the properties of closed circular duplex DNA's. In neutral solutions a scission appears to generate a swivel in the complementary strand at a site in the helix opposite to the scission. The twists are then released and a slower sedimenting, weakly closed circular duplex is formed. Such circular duplexes exhibit normal melting behavior, and in alkali dissociate to form circular and linear single strands which sediment at different velocities. Weakly closed circular duplexes containing an interruption in each strand are formed by intramolecular cyclization of viral λ-DNA. A third kind of weakly closed circular duplex is formed by reannealing single strands derived from circularly permuted T2 DNA. These reconstituted duplexes again contain an interruption in each strand though not necessarily regularly spaced with respect to each other.
On the Internal Structure of Bacteriophage Lambda
Authors: Kaiser A. D.
Published: May 2004

The structure of bacteriophage lambda has been studied by electron microscopy of negatively stained particles. The phage particles will eject their DNA if they are heated or dialyzed against a chelating agent. The ghost particles, so formed, have a channel running down their tails. Since the channel is not visible in normal particles, the channel may be filled with part of the DNA molecule. Up to 30% of the ghosts contain round objects about half the internal diameter of the head. The round objects, called "cores," have the same buoyant density as the coat protein. The core may be a protein spool about which the phage DNA is wound.
The Effect of Potassium on the Intestinal Transport of Glucose
Authors: Csáky T. Z. , Ho P. M.
Published: May 2004

The rate of absorption of glucose, galactose, and 3-0-methylglucose was studied in the rat's small intestine perfused in situ with isosmotic solutions containing these sugars and Na2SO4 or K2SO4. The presence of high [K+] in the lumen enhances absorption of glucose but not that of galactose or of 3-0-methylglucose. The potassium stimulation is apparent at higher glucose concentrations where primarily carrier-mediated diffusion is involved in the translocation. In this case potassium stimulates transport even if it is the only cation in the lumen. The potassium-stimulated intestine produces more glycogen with higher specific activity than the control gut. Lactic acid production by the intestine is markedly enhanced if the intestinal lumen is perfused with a solution containing glucose and high [K+]. It is concluded that potassium does not affect permeability or the specific sugar transport system of the gut, but enhances intracellular metabolic disappearance of glucose thereby creating a larger luminal intracellular concentration gradient which in turn enhances the rate of carrier-facilitated entry.
The Effect of Intracellular Current Pulses in Smooth Muscle Cells of the Guinea Pig Vas Deferens at Rest and during Transmission
Authors: Bennett M. R.
Published: May 2004

The effect of intracellular current pulses on the membrane of smooth muscle cells of the guinea pig vas deferens at rest and during transmission was studied. Two main response types were identified: active response cells, in which a spike was initiated in response to depolarizing currents of sufficient strength and duration; passive response cells, in which depolarizing currents gave only electrotonic potential changes. These cells were three times more numerous than the active response cells. During the crest of the active response the input resistance fell by about 25% of the resting value. Comparison of the active response with the action potential due to stimulating the hypogastric nerve showed that the former was smaller in amplitude and had a slower rate of rise and higher threshold. Electrical coupling occurred between the smooth muscle cells during the propagation of the action potential. Depolarizing current pulses had no effect on the amplitude of the excitatory junction potential (E.J.P.) in passive response cells, but in general did decrease its amplitude in active response cells. These results are discussed with respect to the mechanism of autonomic neuroeffector transmission.
A New Approach to Molecular Configuration Applied to Aqueous Pore Transport
Authors: Soll Andrew H.
Published: May 2004

A cylindrical treatment of the configuration of small molecules in solution has been proposed. Cylindrical dimensions were obtained from Fisher-Hirschfelder molecular models, and these dimensions were used in an analysis of three sets of reflection coefficient values from the literature. The correlation between solute dimensions and the reflection coefficient was subjected to both statistical analyses and graphical examination, with particular emphasis given to parameter interdependence. The results consistently indicated a significant relation between the reflection coefficient and solute diameter. The dependence on diameter suggests a lengthwise orientation of solute within the membrane. Furthermore it is shown that this orientation is occurring within the aqueous region of the membrane, and thus this region has a structural characteristic which is responsible for the lengthwise orientation of solute.
Long Duration Responses in Squid Giant Axons Injected with 134Cesium Sulfate Solutions
Authors: Sjodin R. A.
Published: May 2004

Giant axons from the squid were injected with 1.5 M cesium sulfate solutions containing the radioactive isotopes 42K and 134Cs. These axons, when stimulated, gave characteristic long duration action potentials lasting between 5 and 45 msec. The effluxes of 42K and 134Cs were measured both under resting conditions and during periods of repetitive stimulation. During the lengthened responses there were considerable increases in potassium efflux but only small increases in cesium efflux. The selectivity of the delayed rectification process was about 9 times greater for potassium ions than for cesium ions. The data suggest that internal cesium ions inhibit the outward potassium movement occurring during an action potential. The extra potassium effluxes taking place during excitation appear to be reduced in the presence of cesium ions to values between 7 and 22% of those expected in the absence of cesium inhibition.
Exchange Diffusion Effect and Euryhalinity in Teleosts
Authors: Motais R. , Garcia F. , Maetz Romeu J.
Published: May 2004

The sea water (SW)-adapted euryhaline Platichthys flesus, and the marine Serranus exchange about 50% of their internal sodium with the external sodium per hour. This rate of exchange decreases with decreasing salinity of the adaptation medium. When the flounder is transferred from SW to FW an instantaneous 90% reduction of the Na and Cl outflux is observed. About 30 min later a second, progressive, reduction occurs. The outflux reductions appear to result from two types of regulatory mechanisms reducing gill permeability and preventing excessive salt loss. The first reduction corresponds to independent "Na- and Cl-free effects" as shown by transfers to artificial media containing either Na or Cl with an impermeant co-ion. The pattern of simultaneous rapid variations of Na influx and outflux for a range of salinity changes in flounder adapted to SW, ½ SW, or ¼ SW has been studied. The data are compatible with the hypothesis of an exchange diffusion mechanism characterized by a coupling of both unidirectional fluxes. The affinity of the exchange diffusion carrier for sodium has been measured (Km ≃ 400 mM). The delayed reduction would result from a progressive diminution of the quantity of carrier available but without modification of its affinity for sodium. When the stenohaline marine perch is transferred from SW to FW, a 40% reduction of the outflux is observed. But it is not the result of an exchange diffusion effect as it is related to the external osmolarity change and not to the NaCl concentration change. Furthermore no delayed reduction is observed after transfer into FW. This transfer is accompanied by a heavy loss of electrolytes resulting in a rapid decline of the plasma electrolyte level and death. A comparative survey of the relative importance of these regulatory mechanisms has been made.
Osmometrically Determined Characteristics of the Cell Membrane of Squid and Lobster Giant Axons
Authors: Freeman Alan R. , Reuben John P. , Brandt Philip W. , Grundfest Harry
Published: May 2004

Lobster and squid giant nerve fibers respond differently when subjected to osmotic challenges. The axons proper, as distinct from the total (fiber) complex formed by the axon and connective sheath, both behave as "fast" osmometers for changes in the concentration of NaCl, but the maximum degree of swelling in hyposmotic media is by about 60% in lobster and only by 20% in squid. The relative volume intercepts of the van't Hoff relation are about 0.2 for lobster and 0.4 for squid. The sheaths of both axons undergo only small, apparently passive changes in volume. Lobster axons are permeable to Cl, but squid axons are impermeable to this anion. Lobster axons are also permeable to glycerol. The implications of the data as to the nature of volume regulation of cells are discussed.
Effect of Ions on the Efflux of Acetylcholine from Peripheral Nerve
Authors: Dettbarn Wolf-D. , Rosenberg Philip
Published: May 2004

The nerves from the walking leg of lobster released acetylcholine (ACh) even when the ends were tied off, although this release was significantly increased when the nerve endings were not tied. The resting nerves were kept in sea water containing physostigmine. In absence of physostigmine no ACh was found in the surrounding fluid. Removal of Ca from the sea water reduced the release of ACh, while increased concentrations of Ca had no significant effect. Removal of Mg++ or increased Mg++ concentrations in the presence of normal Ca++ concentrations increased the release of ACh. Increased K+ concentrations had a stimulating action on the efflux of ACh. Increased or reduced Na+ concentrations had only slight effects on the release of ACh in resting lobster nerve. During the 4 hr observation period the excised nerves were still able to synthesize ACh. The choline acetylase activity was stimulated by increased concentrations of Mg++ and K+. The effects of ions on the release of ACh are similar to those reported at the junction.
Time Course of TEA+-Induced Anomalous Rectification in Squid Giant Axons
Authors: Armstrong Clay M.
Published: May 2004

Changes in the voltage clamp currents of squid giant axons wrought by low axoplasmic TEA+ (tetraethylammonium chloride) concentrations (0.3 mM and above) are described. They are: (a) For positive steps from the resting potential in sea water, the K+ current increases, decreases, then increases, instead of increasing monotonically. (b) For positive steps from the resting potential in 440 mM external K+, the current has an exponentially decaying component, whose decay rate increases with axoplasmic [TEA+]. The control currents increase monotonically. (c) For negative steps from the resting potential in 440 mM external K+, the current record has a peak followed by a decay that is slow relative to the control. The control record decreases monotonically. Qualitatively these findings can be described by a simple kinetic model, from which, with one assumption, it is possible to calculate the rate at which K+ ions move through the K+ channels. An interesting conclusion from (c) is that the channels cannot be closed by the normal voltage-sensitive mechanism (described by Hodgkin and Huxley) until they are free of TEA+.
Tracer and Nontracer Potassium Fluxes in Squid Giant Axons and the Effects of Changes in External Potassium Concentration and Membrane Potential
Authors: Sjodin R. A. , Mullins L. J.
Published: May 2004

The efflux of labeled and unlabeled potassium ions from the squid giant axon has been measured under a variety of experimental conditions. Axons soaked in sea water containing 42K ions lost radioactivity when placed in inactive sea water according to kinetics which indicate the presence of at least two cellular compartments. A rapidly equilibrating superficial compartment, probably the Schwann cell, was observed to elevate the specific activity of 42K lost from such axons to K-free sea water for a period of hours. The extra radioactive potassium loss from such axons during stimulation, however, was shown to have a specific activity identical within error to that measured in the axoplasm at the end of the experiment. The same was shown for the extra potassium loss occurring during passage of a steady depolarizing current. Axons placed in sea water with an elevated potassium ion concentration (50 mM) showed an increased potassium efflux that was in general agreement with the accompanying increase in membrane conductance. The efflux of potassium ions observed in 50 mM K sea water at different membrane potentials did not support the theory that the potassium fluxes obey the independence principle.
Phenomenological Description of Active Transport of Salt and Water
Authors: Hoshiko T. , Lindley Barry D.
Published: May 2004

The phenomenological definition of active transport by Kedem and the methods of Kedem and Katchalsky have been used to obtain practical equations describing active transport in the single salt and bi-ionic systems. Procedures were devised to evaluate the required set of 10 coefficients for the single salt case and 15 for the bi-ionic. Three of these coefficients are unusual. They express the effects of active transport, i.e. of entrainment between metabolism and the conventional transport flows: active salt transport coefficient, a volume pump coefficient, and an electrogenicity coefficient. In the bi-ionic case a new passive coefficient, λ, was used to express the linkage between the fluxes of the two salts. However, if primary active transport involves only one ion, for example in the bi-ionic case, 12 coefficients suffice and certain relations can be predicted between the practical coefficients. Particular types of primary active transport could be identified by this means. The relation of active transport to membrane electrogenesis was also examined and the flux ratio equation was rederived in terms of the practical coefficients. Applications to specific parallel and series membrane systems have been analyzed.
Analysis of Compound Postsynaptic Potentials in the Central Nervous System of the Surf Clam
Authors: Mellon DeForest
Published: May 2004

Compound postsynaptic potentials, comprising graded excitatory-inhibitory sequences, are the characteristic mode of response to afferent input exhibited by a population of cells in the visceroparietal ganglion of Spisula. Experimentally induced interaction between the phases of the response indicates that the observed sequential invasion represents differences in individual component latencies, rather than the physiological resultant of two separate processes having simultaneous onset but different rates of decay. Excitation is depressed by changes in membrane conductance throughout the duration of the inhibitory phase; moreover, since similar pathways from the periphery initiate both phases, excitatory events are limited to a duration roughly equal in length to the latency for the inhibition. Within this interval repetitive volleys can evoke summation of excitatory events. The inhibitory mechanism is temporally stable, however, and dominates the membrane during repetitive trains of volleys at 1 to 100 per sec. Artificially generated increases in the membrane potential decrease the IPSP while increasing the amplitude of the EPSP. Thus, both phases of the compound response appear to result from events occurring at chemically transmitting synaptic loci. Evidence is presented that these events are driven via collaterals of the same afferent fibers. The behavioral role of these response sequences is uncertain. Analogies, in terms of some observed reflex activity in these clams, appear to exist but presently lack experimental verification.
Pacemaker Potentials for the Periodic Burst Discharge in the Heart Ganglion of a Stomatopod, Squilla oratoria
Authors: Watanabe Akira , Obara Shosaku , Akiyama Toyohiro
Published: May 2004

From somata of the pacemaker neurons in the Squilla heart ganglion, pacemaker potentials for the spontaneous periodic burst discharge are recorded with intracellular electrodes. The electrical activity is composed of slow potentials and superimposed spikes, and is divided into four types, which are: (a) "mammalian heart" type, (b) "slow generator" type, (c) "slow grower" type, and (d) "slow deficient" type. Since axons which are far from the somata do not produce slow potentials, the soma and dendrites must be where the slow potentials are generated. Hyperpolarization impedes generation of the slow potential, showing that it is an electrically excitable response. Membrane impedance increases on depolarization. Brief hyperpolarizing current can abolish the plateau but brief tetanic inhibitory fiber stimulation is more effective for the abolition. A single stimulus to the axon evokes the slow potential when the stimulus is applied some time after a previous burst. Repetitive stimuli to the axon are more effective in eliciting the slow potential, but the depolarization is not maintained on continuous stimulation. Synchronization of the slow potential among neurons is achieved by: (a) the electrotonic connections, with periodic change in resistance of the soma membrane, (b) active spread of the slow potential, and (c) synchronization through spikes.
The Role of Membrane Phosphoglycerate Kinase in the Control of Glycolytic Rate by Active Cation Transport in Human Red Blood Cells
Authors: Parker John C. , Hoffman Joseph F.
Published: May 2004

When the internal Na of human red cells is raised, both K influx and lactate production increase and become more sensitive to the inhibitory action of ouabain. This occurs with either glucose or purine nucleoside as substrate. Fresh whole hemolysates enriched with Na and Mg will convert intermediates above the triose phosphate dehydrogenase step to lactate at a rate which is slowed by ouabain. Intermediates beyond the phosphoglycerate kinase step (PGK) are metabolized at a very rapid rate which is not affected by ouabain. No metabolic effects of ouabain were found in ghost-free hemolysates. Hemoglobin-free ghosts were shown to have both triose phosphate dehydrogenase and PGK activity. The rate of this two-enzyme sequence was found to be a function of the ADP concentration, being maximal when ADP > 0.35 mM. Initial addition of ATP to the ghost system rendered the forward rate of the sequence sensitive to the inhibitory action of ouabain. When the sequence was run in reverse, no inhibitory effect of ouabain could be demonstrated. It is concluded that membrane PGK is a point at which the Na-K transport system can influence the metabolic rate and that this action is possibly exerted via a compartmentalized form of ADP which is an immediate substrate for the ghost PGK.
Discrimination between Alkali Metal Cations by Yeast
Authors: Armstrong W. McD. , Rothstein A.
Published: May 2004

K+ is a competitive inhibitor of the uptake of the other alkali metal cations by yeast. Rb+ is a competitive inhibitor of K+ uptake, but Li+, Na+, and Cs+ act like H+. At relatively low concentrations they behave as apparent noncompetitive inhibitors of K+ transport, but the inhibition is incomplete. At higher concentrations they inhibit the remaining K+ transport competitively. Ca++ and Mg++ in relatively low concentrations partially inhibit K+ transport in an apparently noncompetitive manner although their affinity for the transport site is very low. In each case, in concentrations that produce "noncompetitive" inhibition, very little of the inhibiting cation is transported into the cell. Competitive inhibition is accompanied by appreciable uptake of the inhibiting cation. The apparently noncompetitive effect of other cations is reversed by K+ concentrations much higher than those necessary to essentially "saturate" the transport system. A model is proposed which can account for the inhibition kinetics. This model is based on two cation-binding sites for which cations compete, a carrier or transporting site, and a second nontransporting (modifier) site with a different array of affinities for cations. The association of certain cations with the modifier site leads to a reduction in the turnover of the carrier, the degree of reduction depending on the cation bound to the modifier site and on the cation being transported.
Alanine and Sodium Fluxes Across Mucosal Border of Rabbit Ileum
Authors: Schultz Stanley G. , Curran Peter F. , Chez Ronald A. , Fuisz Robert E.
Published: May 2004

Unidirectional influxes of L-alanine and Na from the mucosal solution into the epithelium of in vitro rabbit ileum have been determined. In the presence of 140 mM Na, alanine influx is approximately 2.2 µmoles/hr cm2, but is inhibited if the NaCl in the mucosal solution is replaced by choline Cl, Tris-Cl, mannitol, LiCl, or KCl. Although alanine influx is strongly dependent upon Na in the mucosal solution, it is uninfluenced by marked reduction of intracellular Na pools. In addition, alanine influx is unaffected by intracellular alanine concentration. Na influx is markedly inhibited by the presence of Li. Evidence is presented that Na transport across the mucosal border cannot be attributed to simple diffusion even though the net flux across this surface is in the direction of the electrochemical potential difference.
Kinetic Relations of the Na-Amino Acid Interaction at the Mucosal Border of Intestine
Authors: Curran Peter F. , Schultz Stanley G. , Chez Ronald A. , Fuisz Robert E.
Published: May 2004

The relation between unidirectional influxes of Na and amino acids across the mucosal border of rabbit ileum was studied under a variety of conditions. At constant Na concentration in the mucosal bathing solution, amino acid influx followed Michaelis-Menten kinetics permitting determination of maximal influx and the apparent Michaelis constant, Kt. Reduction in Na concentration, using choline as substitute cation, caused an increase in Kt for alanine but had no effect on maximal alanine influx. The reciprocal of Kt was a linear function of Na concentration. Similar results were obtained for valine and leucine and these amino acids competitively inhibited alanine influx both in the presence and in the absence of Na. These results lead to a model for the transport system which involves combination of Na and amino acid with a single carrier or site leading to penetration of both solutes. The model predicts that alanine should cause an increase in Na influx and the ratio of this extra Na flux to alanine flux should vary with Na concentration. The observed relation agreed closely with predicted values for Na concentrations from 5 to 140 mM. These results support the hypothesis that interactions between Na and amino acid transport depend in part on a common entry mechanism at the mucosal border of the intestine.
Nonsolvent Water in Human Erythrocytes
Authors: Cook John S.
Published: May 2004

From the ability of a concentrated suspension of human erythrocytes to regulate the pH of unbuffered, anisotonic, external media it is possible to calculate the fractional cell volume in which chloride is dissolved. The difference between this volume and the total cell water gives the nonsolvent water (for chloride) of the cell. Nonsolvent water is less than 3% of the isotonic cell volume. The quantity of nonsolvent water per cell may increase as the cells shrink in hypertonic solutions.
The Effect of Low Ionic Strength Extracellular Solutions on the Resting Potential in Skeletal Muscle Fibers
Authors: Holtzman David
Published: May 2004

Intracellular measurements of the resting potential were made in fibers of the frog sartorius muscle in solutions of varying salt composition and concentration to determine the effects of low ionic strength extracellular solutions on the resting potential. Changes in the glass microelectrode tip potential in low ionic strength solutions were minimized by adding ThCl4 to the extracellular solution. These experimental conditions allowed measurement of the relationship of the resting potential to the concentration of the salt in the extracellular solution by replacing it with the nonionic substance, sucrose. Substitution of sucrose for the extracellular NaCl produced a stable depolarization which was logarithmically related to the NaCl concentration. Substitution of sucrose for choline Cl, instead of NaCl, produced the same degree of depolarization. When Na salts of anions less permeable than chloride (Br, I, NO3) were used, the resting potentials in 116 mM solutions were close to those with chloride (±3mv). The depolarizations produced in low ionic strength solutions of these salts were significantly less than those with chloride.
Decreased K+ Conductance Produced by Ba++ in Frog Sartorius Fibers
Authors: Sperelakis Nick , Schneider Martin F. , Harris E. J.
Published: May 2004

The action of Ba++ on membrane potential (Em) and resistance (Rm) of frog (R. pipiens) sartorius fibers was studied. In normal Cl- Ringer's, Ba++ (<9 mM) did not depolarize or induce contractions, but increased Rm slightly above the control value of 3.8 ± 0.6 KΩ-cm2. In Cl--free Ringer's (methane sulfonate) Rm was 28.8 ± 2.8 KΩ-cm2, and low concentrations of Ba++ (0.05–5.0 mM) depolarized and induced spontaneous contractions (fibrillation), even in tetrodotoxin. To stop disturbance of the microelectrodes, contractions were prevented by using two Cl--free solutions: (a) twice hypertonic with sucrose (230 mM), or (b) high K+ (83 mM) partially replacing Na+. In the hypertonic solution, the fiber diameters decreased, Em increased slightly, and Rm decreased to 9.0 ± 0.6 KΩ-cm2 (perhaps due to swelling of sarcotubules). Ba++ (0.5 mM) rapidly increased Rm to 31.3 ± 3.8, decreased Em (e.g., to -30 mv), and induced spontaneous "action potentials;" Sr++ had no effect. In the high K+ solution, the fibers were nearly completely depolarized, and Rm was decreased markedly to 1.5 ± 0.2 KΩ-cm2; Ba++ increased Rm to 6.7 ± 0.5 KΩ-cm2. The Ba++ actions usually began within 0.5 min and reached a maximum within 5 min. Addition of SO4=, to precipitate the Ba++, rapidly reversed the increase in Rm. Ba++ must act by decreasing K+ conductance (gK). In Cl- Ringer's, the high gCl/gK ratio masked the effect of Ba++ on gK. Thus, small concentrations of Ba++ specifically and rapidly decrease gK.
Effects of Cardiac Glycosides on Electrical Activity in the Isolated Retina of the Frog
Authors: Frank Robert N. , Goldsmith Timothy H.
Published: May 2004

Ouabain added to physiological salt solutions bathing the isolated frog retina irreversibly abolishes the electrical response to light (the electroretinogram or ERG). The time course of abolition depends on the concentration of ouabain in the medium and the surface of the retina to which it is applied. When the glycoside is placed on the receptor surface, in 7 min the ERG is completely eliminated by 10-4 M ouabain and more than 90% inhibited by 3 x 10-5 M ouabain. The effect is slower at lower concentrations and when the solution is applied to the vitreous surface of the retina. The evidence suggests that abolition of the ERG by ouabain is due principally to inhibition of the active transport of sodium: (a) Structurally modified glycosides which are considerably less potent inhibitors of alkali cation-activated ATPase activity in preparations of frog retinal outer segments are also poorer inhibitors of electrical activity in isolated retinas. (b) Replacing much of the sodium in the medium bathing the retina by choline, Tris, or sucrose significantly protects the retina from ouabain. It is suggested that in a standard sodium environment essentially constant activity of the sodium pump is required to prevent rapid and irreversible change. The cellular sites most critically dependent on the sodium pump have not been identified.
Ion Transport in Hydrodictyon africanum
Authors: Raven J. A.
Published: May 2004

The concentrations of K, Na, and Cl in the cytoplasm and vacuole, the tracer fluxes of these ions into and out of the cenocyte, and the electrical potential difference between bathing solution and vacuole and cytoplasm, have been measured in Hydrodictyon africanum. If the ions were acted on solely by passive electrochemical forces, a net efflux of K and Cl and a net influx of Na would be expected. Tracer fluxes indicate a net influx of K and Cl and efflux of Na in the light; these net fluxes are consequently active, with an obligate link to metabolism. The effects of darkness and low temperature indicate that most of the tracer K and Cl influx and Na efflux are linked to metabolism, while the corresponding tracer fluxes in the direction of the free energy gradient are not. Ouabain specifically inhibits the metabolically linked portions of tracer K influx and Na efflux. Alterations in the external K concentration have similar effects on metabolically mediated K influx and Na efflux. It would appear that K influx and Na efflux are linked, at least in the light.
Light Stimulation of Active Transport in Hydrodictyon africanum
Authors: Raven J. A.
Published: May 2004

The mechanism of light stimulation of active K and Cl influx and active Na efflux, in Hydrodictyon africanum has been investigated using different wavelengths of red light and different gas mixtures, and the inhibitors DCMU and CCCP. The active Cl influx requires photosystem 2, since its relative quantal efficiency falls with increasing wavelength of red light, and it is as sensitive to the inhibitor DCMU as is photosynthesis; it is relatively insensitive to the uncoupler CCCP. The active K influx and active Na efflux are inhibited by CCCP, but the relative quantal efficiency of these processes increases with increasing wavelength of red light, and they are relatively insensitive to DCMU. These cation fluxes can be supported by cyclic photophosphorylation, whereas Cl influx needs photosystem 2 but probably not ATP.
Cation Transport in Escherichia coli
Authors: Weiden Paul L. , Epstein Wolfgang , Schultz Stanley G.
Published: May 2004

When Escherichia coli K-12 is grown in media containing limiting amounts of K, growth continues normally until all the extracellular K has been consumed. Thereafter the rates of growth, glucose consumption, and oxygen consumption decrease progressively, and the cell contents of K and P fall. These changes, referred to as K limitation, are all reversed by the addition of K. By specifically altering the ionic composition of the cells it was shown that these metabolic disturbances are not due to changes in the cell content of K or Na, but are directly related to the absence of K from the extracellular medium. The cell pool of inorganic P and the uptake of PO4 from the medium are low in K-limited cells and are immediately stimulated by the addition of K, suggesting that the primary effect of K limitation is to inhibit PO4 uptake. All the metabolic effects of K limitation can be attributed to inhibition of PO4 uptake. The requirement of extracellular K for PO4 uptake may be due to a coupling between the uptake of K and PO4.
Factors Influencing Glucose Flux and the Effect of Insulin in Cultured Human Cells
Authors: Hay Robert J. , Paul John
Published: May 2004

Uptake of glucose-3H into cultured HLM cells was measured. Equilibration of intracellular and extracellular pools occurred after 25 min. Glucose influx was determined subsequently by measuring the glucose-3H entering in precisely 1 min. Although saturation kinetics were demonstrated these were not of the simple Michaelis-Menten type. The Km of the glucose carrier system is probably about 60 mM glucose. Galactose did not compete with glucose. Insulin stimulated glucose flux without increasing the value of Vmax. The stimulation was fully demonstrable after 10 min, could be elicited at concentrations of 10-4 units/ml, and was absent 2–4 hr after removal. Increasing pH had little or no effect in stimulating glucose flux. Increasing osmotic pressure caused a marked increase and reduced the effect of insulin. Glucose influx was unaffected by anoxia. Glucose influx was increased and the effect of insulin abolished in the absence of K+. Glucose influx was increased by mercuric chloride, iodoacetate, and fluoride which abolished the effect of insulin. Dinitrophenol decreased the rate of glucose uptake but did not alter the effect of insulin. Phlorizin reduced the rate of glucose uptake and abolished the effect of insulin. ATP and AMP enhanced the rate of glucose uptake. These findings are discussed in relation to the mode of action of insulin.
Cation Movements in the High Sodium Erythrocyte of the Cat
Authors: Sha'afi R. I. , Lieb W. R.
Published: May 2004

The uptake of 42K and 24Na by cat erythrocytes was investigated. Under steady-state conditions, the nontransient component of 42K influx was found to be 0.18 ± 0.01 meq/liter RBC/hr and insensitive to ouabain (100 µM); the corresponding value for 24Na was 17 ± meq/liter RBC/hr. A study was made of the effects of anions upon cation movements in these and other mammalian red cells. Iodide was found to inhibit markedly (>50%) Na inward movements in cat and dog but not in the other erythrocytes. An increase (15–30%) in K uptake in the presence of iodide was noted in all the mammalian cells studied.
Some Fundamental Molecular Mechanisms of Contractility in Fibrous Macromolecules
Authors: Mandelkern L.
Published: May 2004

The fundamental molecular mechanisms of contractility and tension development in fibrous macromolecules are developed from the point of view of the principles of polymer physical chemistry. The problem is treated in a general manner to encompass the behavior of all macromolecular systems irrespective of their detailed chemical structure and particular function, if any. Primary attention is given to the contractile process which accompanies the crystal-liquid transition in axially oriented macromolecular systems. The theoretical nature of the process is discussed, and many experimental examples are given from the literature which demonstrate the expected behavior. Experimental attention is focused on the contraction of fibrous proteins, and the same underlying molecular mechanism is shown to be operative for a variety of different systems.
Contractility and Conformation
Authors: Scheraga Harold A.
Published: May 2004

Contractility in fibers can arise from changes of macromolecular conformation caused by changes in some thermodynamic variable such as temperature, pH, or solvent composition. Illustrations are given of contractile processes in fibers and of changes in macromolecular conformation in dilute solution. These may involve order-disorder transitions, e.g. of the type exhibited by the helix-coil transition. A statistical mechanical treatment of the helix-coil transition involves the assignment of statistical weights to various states and the proper counting of these statistical weights in the formation and evaluation of the partition function; the thermodynamic properties of the system are derivable from the partition function. The counting procedure involved in the consideration of the α-helix and random coil is described. In addition, the factors affecting the relative stabilities of various helical conformations are discussed. These considerations of macromolecular conformation provide a basis for discussing contractile mechanisms in which changes of conformation are involved.