bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses of Photoreceptors in Hermissenda
Authors: Alkon Daniel L. , Fuortes M. G. F.
Published: May 2004

The five photoreceptors in the eye of the mollusc Hermissenda crassicornis respond to light with depolarization and firing of impulses. The impulses of any one cell inhibit other cells, but the degree of inhibition differs in different pairs. Evidence is presented to show that the interactions occur at terminal branches of the photoreceptor axons, inside the cerebropleural ganglion. Properties of the generator potential are examined and it is shown that the depolarization develops in two phases which are affected differently by extrinsic currents. Finally, it is shown that by enhancing the differences in the responses of individual cells to a variety of stimuli, the interactions may facilitate a number of simple discriminations.
Calcium and Facilitation at Two Classes of Crustacean Neuromuscular Synapses
Authors: Linder Thomas M.
Published: May 2004

The closer muscle of the crab, Chionoecetes, has at least two classes of excitatory neuromuscular synapses. In one class of synapses an action potential depolarizing the synaptic region releases much more transmitter if it has been preceded recently by another action potential. The other class of synapses shows this property, called facilitation, to a far lesser extent. Immediately after one conditioning stimulus the level of facilitation is similar in both classes. The rate of the ensuing decay of the facilitation is the critical factor differentiating the two classes of synapses. The relationship between external Ca++ concentration and transmitter release is similar for both classes of synapses. The slope of a double logarithmic plot of this relationship varies from 3.1 between 5 and 10 mM Ca++ to 0.9 between 30 and 40 mM Ca++. Facilitation does not significantly change when tested in external Ca++ concentrations ranging from 7 to 30 mM. The extracellularly recorded nerve terminal action potential does not increase in amplitude during facilitation. The results suggest that the mechanism of synaptic facilitation is similar for both classes of synapses and occurs after the stage in transmitter release involving Ca++.
An Analysis of the Leakages of Sodium Ions into and Potassium Ions out of Striated Muscle Cells
Authors: Sjodin R. A. , Beaugé L. A.
Published: May 2004

Net sodium influx under K-free conditions was independent of the intracellular sodium ion concentration, [Na]i, and was increased by ouabain. Unidirectional sodium influx was the sum of a component independent of [Na]i and a component that increased linearly with increasing [Na]i. Net influx of sodium ions in K-free solutions varied with the external sodium ion concentration, [Na]o, and a steady-state balance of the sodium ion fluxes occurred at [Na]o = 40 mM. When solutions were K-free and contained 10-4 M ouabain, net sodium influx varied linearly with [Na]o and a steady state for the intracellular sodium was observed at [Na]o = 13 mM. The steady state observed in the presence of ouabain was the result of a pump-leak balance as the external sodium ion concentration with which the muscle sodium would be in equilibrium, under these conditions, was 0.11 mM. The rate constant for total potassium loss to K-free Ringer solution was independent of [Na]i but dependent on [Na]o. Replacing external NaCl with MgCl2 brought about reductions in net potassium efflux. Ouabain was without effect on net potassium efflux in K-free Ringer solution with [Na]o = 120 mM, but increased potassium efflux in a medium with NaCl replaced by MgCl2. When muscles were enriched with sodium ions, potassium efflux into K-free, Mg++-substituted Ringer solution fell to around 0.1 pmol/cm2·s and was increased 14-fold by addition of ouabain.
Effects of Rapid Cooling on the Mechanical and Electrical Activities of Smooth Muscles of Guinea Pig Stomach and Taenia Coli
Authors: Magaribuchi T. , Ito Y. , Kuriyama H.
Published: May 2004

The effects of rapid cooling on the mechanical and electrical activities of the guinea pig taenia coli and circular muscle of the stomach were investigated. Lowering the temperature from 32° to 10°C (cold shock) depolarized the membrane and increased the membrane resistance in both tissues. However, in the taenia coli, an initial reduction of membrane resistance was observed. In both tissues, contracture evoked by cold shock and rapid relaxation after rewarming, preceded the changes of membrane properties. Displacements of the membrane potential did not modify the amplitude of contracture under cold shock. Caffeine and thymol modified the membrane properties, but the effects of cold shock were still observed. The effects of cold shock were also observed on K-induced contracture. It was postulated that at least two different sites of sequestered bound Ca are located in these smooth muscles and are responsible for evoking the mechanical response. One component possesses a close relation to membrane and the other component is presumably sequestered within the muscle.
Graded Activation in Frog Muscle Fibers
Authors: Costantin L. L. , Taylor S. R.
Published: May 2004

The membrane potential of frog single muscle fibers in solutions containing tetrodotoxin was controlled with a two-electrode voltage clamp. Local contractions elicited by 100-ms square steps of depolarization were observed microscopically and recorded on cinefilm. The absence of myofibrillar folding with shortening to striation spacings below 1.95 µm served as a criterion for activation of the entire fiber cross section. With depolarizing steps of increasing magnitude, shortening occurred first in the most superficial myofibrils and spread inward to involve axial myofibrils as the depolarization was increased. In contractions in which the entire fiber cross section shortened actively, both the extent of shortening and the velocity of shortening at a given striation spacing could be graded by varying the magnitude of the depolarization step. The results provide evidence that the degree of activation of individual myofibrils can be graded with membrane depolarization.
The Reponse of Duck Erythrocytes to Norepinephrine and an Elevated Extracellular Potassium
Authors: Kregenow Floyd M.
Published: May 2004

This paper presents evidence that duck erythrocytes regulate their size in isotonic media by utilizing a previously reported "volume-controlling mechanism." Two different experimental situations are examined. In the first, cells enlarge in a solution containing norepinephrine and an elevated [K]o; and in the second, enlarged cells shrink to their original size if the norepinephrine and excess potassium are removed. As the erythrocytes enlarge, K, Cl, and H2O accumulate. Shrinkage, in contrast, is accompanied by the controlled loss of K, Cl, and H2O. These changes and the associated changes in membrane permeability resemble those reported previously when duck erythrocytes incubate in anisotonic media. There cells, after first shrinking or swelling, utilize a "volume-controlling mechanism" to reestablish their original size. The mechanism regulates cell size by adjusting the total number of osmotically active intracellular particles. The present studies indicate duck red cells use this mechanism to readjust their total monovalent cation content and thus their solute content in isotonic media as well. In addition, evidence is presented which indicates that the "volume-controlling mechanism" and ouabain-inhibitable cation pump differ functionally.
Light-Evoked and Spontaneous Discrete Waves in the Ventral Nerve Photoreceptor of Limulus
Authors: Yeandle Stephen , Spiegler Joel B.
Published: May 2004

Discrete waves, recorded from the ventral nerve photoreceptor, occur in the light and in the dark. Spontaneous waves, on the average, are smaller than light-evoked waves. This suggests that not all spontaneous waves can arise from spontaneous changes in the visual pigment molecule identical to changes induced by photon absorption. Spontaneous and light-evoked waves are statistically independent of each other. This is shown by determination of frequency of response as a function of pulse energy for short pulses and determination of the distribution of intervals between waves evoked by steady lights. The available data can be explained by two models. In the first each photon produces a time-dependent excitation that goes to zero the instant the wave occurs so that the number of effective absorptions from a short light pulse equals the number of waves produced by the light pulse. In the second the excitation produced by photon absorption is unaffected by the occurrence of the waves so that the number of waves produced from a short light pulse may be different from the number of effective absorptions. Present results do not allow a choice between the two models.
Ionic Blockage of Sodium Channels in Nerve
Authors: Woodhull Ann M.
Published: May 2004

Increasing the hydrogen ion concentration of the bathing medium reversibly depresses the sodium permeability of voltage-clamped frog nerves. The depression depends on membrane voltage: changing from pH 7 to pH 5 causes a 60% reduction in sodium permeability at +20 mV, but only a 20% reduction at +180 mV. This voltage-dependent block of sodium channels by hydrogen ions is explained by assuming that hydrogen ions enter the open sodium channel and bind there, preventing sodium ion passage. The voltage dependence arises because the binding site is assumed to lie far enough across the membrane for bound ions to be affected by part of the potential difference across the membrane. Equations are derived for the general case where the blocking ion enters the channel from either side of the membrane. For H+ ion blockage, a simpler model, in which H+ enters the channel only from the bathing medium, is found to be sufficient. The dissociation constant of H+ ions from the channel site, 3.9 x 10-6 M (pKa 5.4), is like that of a carboxylic acid. From the voltage dependence of the block, this acid site is about one-quarter of the way across the membrane potential from the outside. In addition to blocking as described by the model, hydrogen ions also shift the responses of sodium channel "gates" to voltage, probably by altering the surface potential of the nerve. Evidence for voltage-dependent blockage by calcium ions is also presented.
Temperature Dependence of Nonelectrolyte Permeation across Red Cell Membranes
Authors: Galey W. R. , Owen J. D. , Solomon A. K.
Published: May 2004

The temperature dependence of permeation across human red cell membranes has been determined for a series of hydrophilic and lipophilic solutes, including urea and two methyl substituted derivatives, all the straight-chain amides from formamide through valeramide and the two isomers, isobutyramide and isovaleramide. The temperature coefficient for permeation by all the hydrophilic solutes is 12 kcal mol-1 or less, whereas that for all the lipophilic solutes is 19 kcal mol-1 or greater. This difference is consonant with the view that hydrophilic molecules cross the membrane by a path different from that taken by the lipophilic ones. The thermodynamic parameters associated with lipophile permeation have been studied in detail. ΔG is negative for adsorption of lipophilic amides onto an oil-water interface, whereas it is positive for transfer of the polar head from the aqueous medium to bulk lipid solvent. Application of absolute reaction rate theory makes it possible to make a clear distinction between diffusion across the water-red cell membrane interface and diffusion within the membrane. Diffusion coefficients and apparent activation enthalpies and entropies have been computed for each process. Transfer of the polar head from the solvent into the interface is characterized by ΔG‡ = 0 kcal mol-1 and ΔS‡ negative, whereas both of these parameters have large positive values for diffusion within the membrane. Diffusion within the membrane is similar to what is expected for diffusion through a highly associated viscous fluid.
Differential Responses of Crab Neuromuscular Synapses to Cesium Ion
Authors: Atwood H. L. , Lang Fred
Published: May 2004

Excitatory postsynaptic potentials (EPSP's) generated in crab muscle fibers by a single motor axon, differ in amplitude and facilitation. Some EPSP's are large at low frequencies of stimulation and show little facilitation; others are smaller and show pronounced facilitation. When K+ is replaced by Cs+ in the physiological solution, all EPSP's increase in amplitude, but small EPSP's increase proportionately more than large ones. Quantal content of transmission, determined by external recording at single synaptic regions, undergoes a much larger increase at facilitating synapses. The increase in quantal content of transmission is attributable to prolongation of the nerve terminal action potential in Cs+. After 1–2 h of Cs+ treatment, defacilitation of synaptic potentials occurs at synapses which initially showed facilitation. This indicates that Cs+ treatment drastically increases the fraction of the "immediately available" transmitter store released by each nerve impulse, especially at terminals with facilitating synapses. It is proposed that facilitating synapses normally release less of the "immediately available" store of transmitter than poorly facilitating synapses. Possible reasons for this difference in performance are discussed.
The Electrical Activity of Canine Cardiac Purkinje Fibers in Sodium-Free, Calcium-Rich Solutions
Authors: Aronson Ronald S. , Cranefield Paul F.
Published: May 2004

Propagated action potentials can be obtained in canine cardiac Purkinje fibers exposed to Na-free solutions containing no inorganic cation other than Ca and K. Essentially similar action potentials are obtained if Na is replaced by tetraethylammonium (TEA), tetramethylammonium (TMA), or choline. In a solution containing 128 mM TEA and 16.2 mM Ca the characteristics of these electrical responses were: maximum diastolic potential, -59 ± 3.3 mV; overshoot, 20 ± 6.8 mV; maximum upstroke velocity, 3.7 ± 2.3 V/s; conduction velocity, 0.1 m/s; and action potential duration, 360 ± 45 ms. The magnitude of the overshoot varied with log Cao with a slope of about 30 mV/10-fold concentration change. The upstroke velocity was an approximately linear function of Cao. The active response was greatly diminished or abolished by Mn and D-600 but was unaffected by tetrodotoxin. These Ca-dependent responses appeared in a region of transmembrane potential (about -50 mV) at which the rapid Na-dependent upstroke is abolished even when Na is present.
Inhibition of Amino Acid Transport in Rabbit Intestine by p-Chloromercuriphenyl Sulfonic Acid
Authors: Schaeffer John F. , Preston Robert L. , Curran Peter F.
Published: May 2004

Influx of phenylalanine across the brush border of rabbit intestine is markedly reduced by treatment with 5 mM p-chloromercuriphenyl sulfonate (PCMBS). The effect is rapidly and completely reversed by dithiothreitol. Phenylalanine influx into PCMBS-treated tissue can be competitively inhibited by other neutral amino acids and follows saturation kinetics. PCMBS causes an increase in the apparent Michaelis constant from the value observed in control tissue but does not alter the maximal influx significantly. Treatment of the tissue with PCMBS leads to a significant reduction in the Na-sensitivity of the transport, and a number of results indicate that the major effect of the reagent is to cause a marked reduction in the affinity of the transport system for Na. The transport system can be partially protected against reaction with PCMBS by phenylalanine and tryptophan but not by methionine or norleucine. The results suggest that PCMBS reacts with a sulfhydryl group in the region of the transport site and may alter conformational changes associated with the binding of substrates.
Intersensory Interactions in Hermissenda
Authors: Alkon Daniel L.
Published: May 2004

Hair cells of the Hermissenda statocyst respond to photic stimulation. This response requires the presence of at least one of the two eyes. Two principal hair cell responses to light were observed. The activity of photoreceptors in response to a light step is interrupted during firing of contralateral hair cells. The intersensory interactions between the statocyst and visual pathway underlying these responses were examined with simultaneous intracellular recordings. Evidence is presented that the statocyst of Hermissenda is an important channel for visual information.
The Quantal Nature of Synaptic Transmission at the Neuromuscular Junction of a Spider
Authors: Brenner H. R. , Rathmayer W.
Published: May 2004

Spontaneous and evoked release of transmitter at neuromuscular junctions in three different leg muscles of a tarantula (Dugesiella hentzi) was investigated. In most cases the spontaneous miniature potentials were released independently, although bursts from single synaptic junctions occasionally occurred. In contrast to recent findings in other arthropod muscles, focal extracellular recording from junctional areas revealed that the evoked release of transmitter quanta followed Poisson's theorem at low quantal content synaptic junctions in arachnid muscles.
Destruction of Sodium Conductance Inactivation in Squid Axons Perfused with Pronase
Authors: Armstrong Clay M. , Bezanilla Francisco , Rojas Eduardo
Published: May 2004

We have studied the effects of the proteolytic enzyme Pronase on the membrane currents of voltage-clamped squid axons. Internal perfusion of the axons with Pronase rather selectively destroys inactivation of the Na conductance (gNa). At the level of a single channel, Pronase probably acts in an all-or-none manner: each channel inactivates normally until its inactivation gate is destroyed, and then it no longer inactivates. Pronase reduces g¯Na, possibly by destroying some of the channels, but after removal of its inactivation gate a Na channel seems no longer vulnerable to Pronase. The turn-off kinetics and the voltage dependence of the Na channel activation gates are not affected by Pronase, and it is probable that the enzyme does not affect these gates in any way. Neither the K channels nor their activation gates are affected in a specific way by Pronase. Tetrodotoxin does not protect the inactivation gates from Pronase, nor does maintained inactivation of the Na channels during exposure to Pronase. Our results suggest that the inactivation gate is a readily accessible protein attached to the inner end of each Na channel. It is shown clearly that activation and inactivation of Na channels are separable processes, and that Na channels are distinct from K channels.
Dark Adaptation and Visual Pigment Regeneration in Human Cones
Authors: Hollins M. , Alpern M.
Published: May 2004

Foveal threshold elevation and red-green cone pigment regeneration have been studied in the dark after a wide range of bleaches in normal man with a view to probing the limits of the application of the Dowling-Rushton relation: i.e., the direct proportionality between log threshold elevation and fraction of unregenerated pigment. Cone pigment regeneration (and threshold recovery) is much faster after short bleaches than expected from the kinetics of a simple monomolecular reaction. Recovery is faster after a fixed (short) duration bleach the weaker it is. Except for the first 30 s after relatively weak bleaches and the entire recovery after a very brief (<0.001 s) saturating bright flash which bleaches a little more than 50%, the results are accurately fit by the Dowling-Rushton relation over the entire range tested with only one arbitrary constant (the proportionality factor). Theory predicts too low threshold in comparison with what is obtained, for both of these exceptions
A Relaxation Oscillator Description of the Burst-Generating Mechanism in the Cardiac Ganglion of the Lobster, Homarus americanus
Authors: Mayeri Earl
Published: May 2004

Properties of the neural mechanism responsible for generating the periodic burst of spike potentials in the nine ganglion neurons were investigated by applying brief, single shocks to the four small cells with extracellular electrodes placed near the trigger zones of the small cells. The shock elicited a burst if presented during the latter portion of the silent period, terminated a burst during the latter portion of the burst period, and was followed by a newly initiated burst during the early portion of the burst period. The resultant changes in burst and silent period durations were quantitatively described by a second-order non-linear differential equation similar to the van der Pol equation for a relaxation oscillator. The equation also qualitatively described changes in firing threshold of the small cells during the burst cycle. The first derivative of the solution to the equation is similar to slow transmembrane potentials in neurons that are involved in generation of burst activity in other crustacean cardiac ganglia.
Mechanical and Electrical Oscillations in Cardiac Muscle of the Turtle
Authors: Bozler Emil , Delahayes J. F.
Published: May 2004

During contractures of the turtle ventricle rapid changes in length induce sinusoidal oscillations under isotonic conditions. They are due to delayed responses to stretching and release, which can be demonstrated also under isometric conditions. Oscillations of two distinct frequencies are produced under different conditions and are distinguished as high- and low-frequency oscillations. In depolarized muscles the frequency is such that the duration of one cycle is about the same as that of a normal twitch, while in high-Ca solutions the duration can be the same as in high-K solutions or about six times lower. As reported previously, twitches are followed by weak mechanical and electrical oscillations. Their frequency agrees with the high-frequency oscillations. The same effects can also be induced by stretching and release. It is suggested that the phenomena observed are due to feedback mechanisms which originate in the contractile mechanism. The high-frequency oscillations are similar to those observed previously in other muscles, particularly insect fibrillar muscle, and are not due to changes in Ca concentration. The other mechanisms involve the membrane and possibly the intracellular Ca stores.
Tension in Skinned Frog Muscle Fibers in Solutions of Varying Ionic Strength and Neutral Salt Composition
Authors: Gordon A. M. , Godt R. E. , Donaldson S. K. B. , Harris C. E.
Published: May 2004

The maximal calcium-activated isometric tension produced by a skinned frog single muscle fiber falls off as the ionic strength of the solution bathing this fiber is elevated declining to zero near 0.5 M as the ionic strength is varied using KCl. When other neutral salts are used, the tension always declines at high ionic strength, but there is some difference between the various neutral salts used. The anions and cations can be ordered in terms of their ability to inhibit the maximal calcium-activated tension. The order of increasing inhibition of tension (decreasing tension) at high ionic strength for anions is propionate- ≃ SO4-- < Cl- < Br-. The order of increasing inhibition of calcium-activated tension for cations is K+ ≃ Na+ ≃ TMA+ < TEA+ < TPrA+ < TBuA+. The decline of maximal calcium-activated isometric tension with elevated salt concentration (ionic strength) can quantitatively explain the decline of isometric tetanic tension of a frog muscle fiber bathed in a hypertonic solution if one assumes that the internal ionic strength of a muscle fiber in normal Ringer's solution is 0.14–0.17 M. There is an increase in the base-line tension of a skinned muscle fiber bathed in a relaxing solution (no added calcium and 3 mM EGTA) of low ionic strength. This tension, which has no correlate in the intact fiber in hypotonic solutions, appears to be a noncalcium-activated tension and correlates more with a declining ionic strength than with small changes in [MgATP], [Mg], pH buffer, or [EGTA]. It is dependent upon the specific neutral salts used with cations being ordered in increasing inhibition of this noncalcium-activated tension (decreasing tension) as TPrA+ < TMA+ < K+ ≃ Na+. Measurements of potentials inside these skinned muscle fibers bathed in relaxing solutions produced occasional small positive values (<6 mV) which were not significantly different from zero.
The Light Growth Response of Phycomyces
Authors: Foster K. W. , Lipson E. D.
Published: May 2004

With the help of an automated tracking system we have studied the characteristics of the transient light growth response of Phycomyces. The response shows a sharply defined latency. The Q10 of the reciprocal latency is 2.4. Response patterns at different peaks of the action spectrum are the same. The gradual variation of response magnitude over a wide range of adapted intensifies parallels that of phototropism. The responses to saturating stimuli exhibit a strong oscillation with a constant period of 1.6 min and variable damping. The growth responses to sinusoidally varying light intensities show a system bandwidth of 2.5 x 10-3 Hz. The linear dependence of phase shift on frequency is largely attributable to the latency observed with pulse stimuli. In the high intensity range a previously suspected increase of the steady-state growth rate with intensity has been confirmed. The light growth responses of mutants selected for diminished phototropism have been investigated. Many of these mutants have sizable but grossly distorted growth responses.
Patterns of Nonelectrolyte Permeability in Human Red Blood Cell Membrane
Authors: Naccache P. , Sha'afi R. I.
Published: May 2004

The permeability of human red cell membrane to 90 different molecules has been measured. These solutes cover a wide spectrum of nonelectrolytes with varying chemical structure, chain length, lipid solubility, chemical reactive group, ability to form hydrogen bonds, and other properties. In general, the present study suggests that the permeability of red cell membrane to a large solute is determined by lipid solubility, its molecular size, and its hydrogen-bonding ability. The permeability coefficient increases with increasing lipid solubility and decreasing ability to form hydrogen bonds, whereas it decreases with increasing molecular size. In the case of small solutes, the predominant diffusion factor is steric hindrance augmented by lipid solubility. It is also found that replacement of a hydroxyl group by a carbonyl group or an ether linkage tends to increase permeability. On the other hand, replacement of a hydroxyl group by an amide group tends to decrease the permeability coefficient.
The Effect of Bathing Solution Tonicity on Resting Tension in Frog Muscle Fibers
Authors: Lännergren J. , Noth J.
Published: May 2004

Resting tension and short-range elastic properties of isolated twitch muscle fibers of the frog have been studied while bathed by solutions of different tonicities. Resting tension in isotonic solution at 2.3-µm sarcomere spacing averaged 0.46 mN·mm-2 and was proportional to the fiber cross-section area. Hypertonic solutions, containing 0.1–0.5 mM tetracaine to block contracture tension, caused a small sustained tension increase, which was proportional to the fiber cross-section area and which reached 0.9 mN·mm-2 at two times normal tonicity (2T). Further increases in tonicity caused little increase in tension. Hypotonic solutions decreased tension. Thus, tension at 2.3 µm is a continuous, direct function of tonicity. The dependence of tension on tonicity lessened at greater sarcomere lengths. At 3.2 µm either a very small rise or, in some fibers, a fall in tension resulted from an increase in tonicity. Hypertonic solutions also decreased the tension of extended sarcolemma preparations. In constant-speed stretch experiments the elastic modulus, calculated from the initial part of the stretch response, rose steeply with tonicity over the whole range investigated (1–2.5T). The results show that tension and stiffness of the short-range elastic component do not increase in parallel in hypertonic solutions.
Muscle Contraction during Hyperpolarizing Currents in the Crab
Authors: Uchitel O. D. , García H.
Published: May 2004

Isolated muscle fibers from the motor legs of the crab Trichodactilus dilocarcinus were submitted to strong hyperpolarizing currents of varied intensities which produced tension during the current pulse. Threshold for tension was obtained with intensities of about 0.2 x 10–5 A, changing Em to ca. –150 mV (starting from a resting potential ofca. –80 mV). At the closure of the anodic square pulse, a second phase of tension usually appeared superimposed upon the one obtained during hyperpolarization. The first phase of tension increased with the increase of Ca++ concentration in the bath. Sr++ produced the same type of mechanical output as Ca++. When added to the normal Ca++ concentration, Ba++ and Mn++ in low concentrations (up to 21.5 mM) also increased the tension of this phase, but at higher concentrations they blocked both phases while Mg++ did not alter the tension. Of all the divalent cations employed, only Sr++ is capable of developing tension as a substitute for Ca++ in the external media. Procaine administered in a dosage (5 x 10–3 W/V)which would suppress the contracture due to caffeine (10 mM), did not modify the tension developed during the hyperpolarization.

The preceding data indicate that the Ca++ required for tension during hyperpolarization comes from sites which would differ from those usually postulated for tension due to depolarization in the muscle fibers of other crustaceans (American crayfish). Furthermore, the external source of Ca++ appears to be one mainly implicated in the induction of tension due to inward current pulses.
Pigment Migration and Adaptation in the Eye of the Squid, Loligo pealei
Authors: Daw N. W. , Pearlman A. L.
Published: May 2004

The migration of the screening pigment was investigated in the retina of the intact squid. The action spectrum of pigment migration corresponds to the action spectrum of the visual pigment, rhodopsin, rather than to the absorption spectrum of the screening pigment. The total number of quanta required for a fixed criterion of pigment migration is the same, when the quanta are delivered over any period of time from 6 s to an hour or more. When less than 3–10% of the rhodopsin is isomerized, the screening pigment migrates out to the tips of the receptors with a time-course of 5–15 min, and back again over the same period of time. When rather more than 10% is isomerized, the outward migration takes 5–15 min, but the screening pigment does not migrate inwards, even after several hours in the dark. Indirect evidence suggests that the band of screening pigment, when it reaches the tips of the receptors, is approximately equivalent to a filter of 0.6 log units. The spectral sensitivity of the optic nerve response was measured, and was found to be broader than the absorption spectrum of squid rhodopsin in vitro; the broadness could be explained by self-screening, assuming a density of rhodopsin of 0.6 log units at 500 nm.
Control of Retinal Sensitivity
Authors: Werblin Frank S.
Published: May 2004

Test stimuli, presented at the center of the bipolar cell receptive field, spanning less than 2 log units of intensity, elicit the full range of graded response. The intensity range of test stimuli that elicits the graded response depends upon the background conditions. A higher range of log test intensities is required to elicit the graded bipolar response in the presence of surround backgrounds. But surround backgrounds can also serve to unsaturate the bipolar response and thereby increase sensitivity under certain conditions. The results suggest that a second stage of sensitivity-control is mediated by the horizontal cell system at the outer plexiform layer, concatenated with the effects of adaptation in the photoreceptors.
Calcium Efflux from Barnacle Muscle Fibers
Authors: Russell J. M. , Blaustein M. P.
Published: May 2004

Calcium-45 was injected into single giant barnacle muscle fibers, and the rate of efflux was measured under a variety of conditions. The rate constant (k) for 45Ca efflux into standard seawater averaged 17 x 10–4 min–1 which corresponds to an efflux of about 1–2 pmol/cm2·s. Removal of external Ca (Cao) reduced the efflux by 50%. In most fibers about 40% of the 45Ca efflux into Ca-free seawater was dependent on external Na (Nao); treatment with 3.5 mM caffeine increased the magnitude of the Nao-dependent efflux. In a few fibers removal of Nao, in the absence of Cao, either had no effect or increased k; caffeine (2–3.5 mM) unmasked an Nao-dependent efflux in these fibers. The Nao-dependent Ca efflux had a Q10 of about 3.7. The data are consistent with the idea that a large fraction of the Ca efflux may be carrier-mediated, and may involve both Ca-Ca and Na-Ca counterflow. The relation between the Nao-dependent Ca efflux and the external Na concentration is sigmoid, and suggests that two, or more likely three, external Na+ ions may activate the efflux of one Ca+2. With a three-for-one Na-Ca exchange, the Na electrochemical gradient may be able to supply sufficient energy to maintain the Ca gradient in these fibers. Other, more complex models are not excluded, however, and may be required to explain some puzzling features of the Ca efflux such as the variable Nao-dependence.
Intestinal Transport of Weak Electrolytes
Authors: Jackson Michael J. , Shiau Yih-Fu , Bane Susan , Fox Margaret
Published: May 2004

A study has been made of the transmural fluxes of benzoic, phenylacetic, and pentanoic acids, benzylamine, hexylamine, and D-amphetamine across rat jejunum incubated in vitro. The M to S fluxes of the weak acids were greater than their corresponding S to M fluxes, and the S to M fluxes of the weak bases were larger than their M to S fluxes. These patterns of asymmetric movements were observed when the transmural electrical potential difference was clamped at 0 mV, and when the pH values of the mucosal and serosal fluids were identical. The effects of a weak acid on the fluxes of other weak electrolytes were qualitatively similar when the effector weak acid was added to the mucosal fluid, and when it was added to the serosal fluid. But the effects of a weak base on the fluxes of other weak electrolytes were dependent upon its location, and the interactions observed when the effector weak base was added to the mucosal fluid were qualitatively different than those seen when it was added to the serosal fluid. The interactions between weak electrolytes could readily be explained in terms of the function of a system of three compartments in series, in which the pH of the intermediate compartment is greater than that of the bulk phases. But these observations could not be explained in terms of an analogous system involving an intermediate compartment of low pH, or in terms of a carrier mediated system. The transport function of the three-compartment system can be described in the form of an equation, and it is found that a pH difference of less than 0.5 unit may explain our observations on weak electrolyte transport.
Action Potential in the Transverse Tubules and Its Role in the Activation of Skeletal Muscle
Authors: Bastian Joseph , Nakajima Shigehiro
Published: May 2004

The double sucrose-gap method was applied to single muscle fibers of Xenopus. From the "artificial node" of the fiber, action potentials were recorded under current-clamping condition together with twitches of the node. The action potentials were stored on magnetic tape. The node was then made inexcitable by tetrodotoxin or by a sodium-free solution, and the wave form of the action potential stored on magnetic tape was imposed on the node under voltage-clamp condition (simulated AP). The twitch height caused by the simulated AP's was always smaller than the twitch height produced by the real action potentials, the ratio being about 0.3 at room temperature. The results strongly suggest that the transverse tubular system is excitable and is necessary for the full activation of twitch, and that the action potential of the tubules contributes to about 70 % of the total mechanical output of the normal isotonic twitch at 20°C. Similar results were obtained in the case of tetanic contraction. At a temperature near 10°C, twitches produced by the simulated AP were not very different (85 % of control amplitude) from the twitches caused by real action potentials. This indicates that the excitability of the tubules becomes less necessary for the full activation of twitch as the temperature becomes lower.
Visual Pigments of Goldfish Cones
Authors: Hárosi Ferenc I. , MacNichol Edward F.
Published: May 2004

Freshly isolated retinal photoreceptors of goldfish were studied microspectrophotometrically. Absolute absorptance spectra obtained from dark-adapted cone outer segments reaffirm the existence of three spectrally distinct cone types with absorption maxima at 455 ± 3,530 ± 3, and 625 ± 5 nm. These types were found often recognizable by gross cellular morphology. Side-illuminated cone outer segments were dichroic. The measured dichroic ratio for the main absorption band of each type was 2–3:1. Rapidly bleached cells revealed spectral and dichroic transitions in regions near 400–410, 435–455, and 350–360 nm. These photoproducts decay about fivefold as fast as the intermediates in frog rods. The spectral maxima of photoproducts, combined with other evidence, indicate that retinene2 is the chromophore of all three cone pigments. The average specific optical density for goldfish cone outer segments was found to be 0.0124 ± 0.0015/µm. The spectra of the blue-, and green-absorbing cones appeared to match porphyropsin standards with half-band width Δν = 4,832 ± 100 cm–1. The red-absorbing spectrum was found narrower, having Δν = 3,625 ± 100 cm–1. The results are consistent with the notion that visual pigment concentration within the outer segments is about the same for frog rods and goldfish cones, but that the blue-, and green-absorbing pigments possess molar extinctions of 30,000 liter/mol cm. The red-absorbing pigment was found to have extinction of 40,000 liter/mol cm, assuming invariance of oscillator strength among the three cone spectra.
Electrophoretic Separation of Different Phophosproteins Associated with Ca-ATPase and Na,K-ATPase in Human Red Cell Ghosts
Authors: Knauf Philip A. , Proverbio Fulgencio , Hoffman Joseph F.
Published: May 2004

Ca has been found to increase the quantity of 32P incorporated into red cell ghosts from [γ-32P]ATP over the levels obtained by incubation with Mg alone or with Mg + Na, in correlation with the effect of Ca on the associated ATPase activities. When the 32P-labeled ghosts were solubilized in sodium dodecyl sulfate (SDS) and electrophoresed on acrylamide gels only two bands could be detected either by autoradiography or by counting the sliced gels. The faster moving band (P-2) had the same mobility and the same molecular weight (103,000) as the phosphoprotein found either with Mg alone or with Mg + Na. The slower moving band (P-1) was not found in extensively washed ghosts labeled in the absence of Ca. The molecular weight of P-1 is approximately 150,000. P-1 like P-2 was not affected by pretreatment of intact cells with Pronase before labeling indicating that neither the phosphorylating mechanism nor the phosphoprotein are accessible to externally applied Pronase. The demonstration that a Ca-phosphoprotein is separable from the Na-stimulated phosphoprotein suggests that the Ca-ATPase is distinct from and independent of the Na,K-ATPase. The fact that Ca blocks the dephosphorylation by K of the Na-phosphoprotein indicates that caution is required in interpreting results when the activities of the different phosphoproteins have not been separately determined.
Ionic Dependence of Reversal Voltage of the Light Response in Limulus Ventral Photoreceptors
Authors: Brown J. E. , Mote M. I.
Published: May 2004

The light-induced current as measured using a voltage clamp (holding voltage at resting potential) is attenuated when sodium ions in the bathing solution, Nao, are replaced by Tris, choline, or Li or when NaCl is replaced by sucrose. After replacement of NaCl by sucrose, the reversal voltage, Vrev, for the light response becomes more negative. In this case, the slope of the Vrev vs. log Nao near Nao = 425 mM is approximately 55 mV/decade increase of Nao (mean for 13 cells). The slope decreases at lower values of Nao. Choline is not impermeant and partially substitutes for Na; the slope of Vrev vs. log Nao is 20 mV/decade (mean for three cells). Vrev does not change when Na is replaced by Li. Decreases in the bath concentrations of Ca, Mg, Cl, or K do not affect Vrev. When Nao = 212 mM, Vrev becomes more positive when Ko is increased. Thus, light induces a change in membrane permeability to Na and probably also to K.
Mechanism for Increase in Intracellular Concentration of Free Calcium in Fertilized Sea Urchin Egg
Authors: Nakamura Masahisa , Yasumasu Ikuo
Published: May 2004

Intracellular free calcium concentration in the sea urchin egg was calculated to increase from 0.1 mM in an unfertilized egg to 1 mM in a fertilized egg 10 min after fertilization, based on measurement of the dissociation constant between free calcium and sea urchin egg homogenate. The dissociation constant between free calcium (dialyzable calcium) and homogenate of sea urchin eggs was measured by means of dialysis equilibrium. The dissociation constant of the unfertilized egg was about 10–4 M and that of the fertilized egg was about 10–3 M in three species of sea urchin, Hemicentrotus pulcherrimus, Anthocidaris crassispina, and Pseudocentrotus depressus. An increase in the dissociation constant of the unfertilized egg homogenate was observed after the addition of calcium ion at a concentration above 0.3 mM, the dissociation constant becoming the same as that observed in the fertilized egg homogenate after the administration of CaCl2 at a concentration above 1 mM. Sodium ion also caused a decrease in the calcium-binding ability of the unfertilized egg homogenate. Therefore, penetration of calcium ion or sodium ion upon fertilization might induce an increase in the dissociation constant and then intracellular concentration of free calcium would increase at fertilization. Almost all calcium-binding ability of the egg homogenate was found in the microsomal fraction, and the substance which bound calcium was thought to be protein in nature, since trypsin could decrease the level of calcium-binding substance in the homogenate of the eggs.
Investigation of the Accompaniment of Calcium During Active Calcium Transport from Human Erythrocyte Ghosts
Authors: Olson Erik J. , Cazort Ralph J.
Published: May 2004

To determine whether a cell metabolite was involved in active calcium transport, the cell contents of human erythrocytes were subjected to high dilutions and the resultant ghosts were checked for their ability to actively transport calcium. It was found that the diluted erythrocyte ghosts did retain their capacity to actively transport calcium and that the characteristics of this transport process appeared to be unaltered by the high dilutions. Calcium analysis of the cell membrane and cell supernatant indicated that almost all of the calcium was lost from the cell solution rather than the cell membrane as active calcium transport proceeded. Therefore it appeared that calcium was able to cross the cell membrane without the aid of a cell metabolite. Investigations with layered erythrocytes indicated that the active transport of calcium was not assisted by centrifugation. Neither inorganic phosphate, pyrophosphate, nor an adenine nucleotide appeared to accompany calcium across the membrane as indicated by total phosphate and inorganic phosphate analysis and 260-nm readings of the deproteinized supernatant.
Solute Flux Coupling in a Homopore Membrane
Authors: Van Bruggen John T. , Boyett June D. , van Bueren Antonia L. , Galey William R.
Published: May 2004

Our previous studies on solute drag on frog skin and synthetic heteropore membranes have been extended to a synthetic homopore membrane. The 150-Å radius pores of this membrane are formed by irradiation and etching of polycarbonate films. The membrane is 6-µm thick and it has 6 x 108 pores cm–2. In this study, sucrose has been used as the driver solute with bulk flow blocked by hydrostatic pressure. As before on heteroporous membranes, the transmembrane asymmetry of tracer solute is dependent on the concentration of the driver solute. Tracer sucrose shows no solute drag while maltotriose shows appreciable solute drag at 1.5 M sucrose. With tracer inulin and dextran, solute drag is detectable at 0.5 M sucrose. These results are in keeping with the previous findings on heteropore membranes. Transmembrane solute drag is the result of kinetic and frictional interaction of the driver and tracer solutes as the driver flows down its concentration gradient. The magnitude of the tracer flux asymmetry is also dependent on the size of the transmembrane pores.
Contractile Activation in Frog Skeletal Muscle
Authors: Costantin L. L.
Published: May 2004

Contractile activation was studied in frog single muscle fibers treated with tetrodotoxin to block action potentials. The membrane potential in a short segment of the fiber was controlled with a two-electrode voltage clamp, and the contractile response of superficial myofibrils in this segment was observed microscopically. The strength-duration relation for contractile activation was similar to that reported by Adrian, Chandler, and Hodgkin (1969); at 3.9°C, the contraction threshold was –44 mV for long depolarizing pulses (100-ms) and increased to +64 mV for 2-ms depolarizations. Hyperpolarizing postpulses shifted the threshold for 2-ms pulses to more positive values, and a similar, but smaller, effect was produced by hyperpolarizing prepulses. The decay of excitability following subthreshold pulses showed two apparently distinct components; at 3.9°C, excitability fell to 50% of its initial value within 4 ms, while the subsequent decline of excitability proceeded with a half-time of about 20 ms.
Effects of Internal Divalent Cations on Voltage-Clamped Squid Axons
Authors: Begenisich Ted , Lynch Carl
Published: May 2004

We have studied the effects of internally applied divalent cations on the ionic currents of voltage-clamped squid giant axons. Internal concentrations of calcium up to 10 mM have little, if any, effect on the time-course, voltage dependence, or magnitude of the ionic currents. This is inconsistent with the notion that an increase in the internal calcium concentration produced by an inward calcium movement with the action potential triggers sodium inactivation or potassium activation. Low internal zinc concentrations (∼1 mM) selectively and reversibly slow the kinetics of the potassium current and reduce peak sodium current by about 40% with little effect on the voltage dependence of the ionic currents. Higher concentrations (∼10 mM) produce a considerable (ca. 90%) nonspecific reversible reduction of the ionic currents. Large hyperpolarizing conditioning pulses reduce the zinc effect. Internal zinc also reversibly depolarizes the axon by 20–30 mV. The effects of internal cobalt, cadmium, and nickel are qualitatively similar to those of zinc: only calcium among the cations tested is without effect.