bluuebunny/crossref_metadata_2025 huggingface dataset:
High Potassium and Low Sodium Contractures in Sheep Cardiac Muscle
Authors: Gibbons W. R. , Fozzard H. A.
Published: May 2004

Contractures develop in sheep atrial trabeculae if Tyrode's solution is rapidly replaced by a solution containing elevated potassium, reduced sodium, or both. Two phases of the contracture can be identified on the basis of differences in physiological behavior: a rapid and transient phase that predominates during the first few seconds of the contracture, and a slowly developed phase that is responsible for the steady level of tension reached later in the contracture. The transient phase is particularly prominent if the muscle is stimulated rapidly before the contracture, and reduced or absent if the muscle is not stimulated or if calcium is not present before the contracture. Recovery of the transient phase after a contracture parallels the recovery of twitches. This transient phase appears to reflect the depolarization-induced release of activator (calcium) from an internal store, possibly the same store that is involved in the normal contraction. The slowly developed tension is dependent on the contracture solution used, and is decreased if the calcium concentration is reduced or if the sodium concentration is increased. It does not depend on conditions before the contracture and does not require time to recover. This phase of the contracture may be due to entry of calcium from the extracellular solution.
Equivalent Circuit of Frog Atrial Tissue as Determined by Voltage Clamp-Unclamp Experiments
Authors: Tarr Merrill , Trank John
Published: May 2004

The equivalent circuit that has been used in the analysis of nerve voltage-clamp data is that of the membrane capacity in parallel with the membrane resistance. Voltage-clamp experiments on frog atrial tissue indicate that this circuit will not suffice for this cardiac tissue. The change in membrane current associated with a step change in membrane potential does not show a rapid spike of capacitive current as would be expected for the simple parallel resistance-capacitance network. Rather, there is a step change in current followed by an exponential decay in current with a time constant of about 1 msec. This relatively slow capacitive charging current suggests that there is a resistance in series with the membrane capacity. A possible equivalent circuit is that of a series resistance external to the parallel resistance-capacitance network of the cell membranes. Another possible circuit assumes that the series resistance is an integral part of the cell membrane. The data presented in this paper demonstrate that the equivalent circuit of a bundle of frog atrial muscle is that of an external resistance in series with the cell membranes.
Temperature Adaptation of Active Sodium-Potassium Transport and of Passive Permeability in Erythrocytes of Ground Squirrels
Authors: Kimzey S. L. , Willis J. S.
Published: May 2004

Unidirectional active and passive fluxes of 42K and 24Na were measured in red blood cells of ground squirrels (hibernators) and guinea pigs (nonhibernators). As temperature is lowered, "active" (ouabain-sensitive) K influx and Na efflux were more greatly diminished in guinea pig cells than in those of ground squirrels. The fraction of total K influx which is ouabain sensitive in red blood cells of ground squirrels was virtually constant at all temperatures, whereas it decreased abruptly in guinea pig cells as temperature was lowered. All the passive fluxes (i.e., Na influx, K efflux, and ouabain-insensitive K influx and Na efflux) decreased logarithmically with decrease in temperature in both species, but in ground squirrels the temperature dependence (Q10 2.5–3.0) was greater than in guinea pig (Q10 1.6–1.9). Thus, red blood cells of ground squirrel are able to resist loss of K and gain of Na at low temperature both because of relatively greater Na-K transport (than in cells of nonhibernators) and because of reduced passive leakage of ions.
The Interaction between Steroid Hormones and Lipid Monolayers on Water
Authors: Gershfeld N. L. , Muramatsu M.
Published: May 2004

The interaction of progesterone, testosterone, androsterone, and etiocholanolone with insoluble lipid films (cholesterol and saturated hydrocarbons containing either alcohol, ester, acetamide, phosphate, amine, or carboxyl groups) was studied. In addition to surface pressure and surface potential measurements of the surface films, radioactive tracers were used to measure the concentration of adsorbed steroid in the lipid films. In general, steroids form mixed films with the insoluble lipid films. Compression of the insoluble lipid films to their most condensed state leads to complete ejection of adsorbed steroid from the surface in all cases except with the amine, for which a small amount of steroid is still retained in the surface. Interactions between the steroids and insoluble lipids are primarily due to van der Waals or dispersion forces; there were no significant contributions from dipole-dipole interactions (except possibly with the amine). Specific interactions between cholesterol and the soluble steroids were not observed. Evidence suggests that low steroid concentrations influence structure of lipid films by altering the hydration layer in the surface film. In contrast to a specific site of action, it is proposed that steroid hormones initiate structural changes in a variety of biological sites; this model of steroid action is consistent with the ubiquity of many steroid hormones.
Polarization of Tryptophan Fluorescence from Single Striated Muscle Fibers
Authors: dos Remedios C. G. , Millikan R. G. C. , Morales M. F.
Published: May 2004

Instrumentation has been developed to detect rapidly the polarization of tryptophan fluorescence from single muscle fibers in rigor, relaxation, and contraction. The polarization parameter (P⊥) obtained by exiciting the muscle tryptophans with light polarized perpendicular to the long axis of the muscle fiber had a magnitude P⊥ (relaxation) > P⊥ (contraction) > P⊥ (rigor) for the three types of muscle fibers examined (glycerinated rabbit psoas, glycerinated dorsal longitudinal flight muscle of Lethocerus americanus, and live semitendinosus of Rana pipiens). P⊥ from single psoas fibers in rigor was found to increase as the sarcomere length increased but in relaxed fibers P⊥ was independent of sarcomere length. After rigor, pyrophosphate produced little or no change in P⊥, but following an adenosine triphosphate (ATP)-containing solution, pyrophosphate produced a value of P⊥ that fell between the contraction and relaxation values. Sinusoidal or square wave oscillations of the muscle of amplitude 0.5–2.0% of the sarcomere length and frequency 1, 2, or 5 Hz were applied in rigor when the myosin cross-bridges are considered to be firmly attached to the thin filaments. No significant changes in P⊥ were observed in either rigor or relaxation. The preceding results together with our present knowledge of tryptophan distribution in the contractile proteins has led us to the conclusion that the parameter P⊥ is a probe of the contractile state of myosin which is probably sensitive to the orientation of the myosin S1 subfragment.
The Influence of Hydrogen Ion Concentration on Calcium Binding and Release by Skeletal Muscle Sarcoplasmic Reticulum
Authors: Nakamaru Yoshiaki , Schwartz Arnold
Published: May 2004

Calcium release and binding produced by alterations in pH were investigated in isolated sarcoplasmic reticulum (SR) from skeletal muscle. When the pH was abruptly increased from 6.46 to 7.82, after calcium loading for 30 sec, 80–90 nanomoles (nmole) of calcium/mg protein were released. When the pH was abruptly decreased from 7.56 to 6.46, after calcium loading for 30 sec, 25–30 nmole of calcium/mg protein were rebound. The calcium release process was shown to be a function of pH change: 57 nmole of calcium were released per 1 pH unit change per mg protein. The amount of adenosine triphosphate (ATP) bound to the SR was not altered by the pH changes. The release phenomenon was not due to alteration of ATP concentration by the increased pH. Native actomyosin was combined with SR in order to study the effectiveness of calcium release from the SR by pH change in inducing super-precipitation of actomyosin. It was found that SR, in an amount high enough to inhibit superprecipitation at pH 6.5, did not prevent the process when the pH was suddenly increased to 7.3, indicating that the affinity of SR for calcium depends specifically on pH. These data suggest the possible participation of hydrogen ion concentration in excitation-contraction coupling.
Polypeptide Secretion from the Isolated Parietovisceral Ganglion of Aplysia californica
Authors: Arch S.
Published: May 2004

In vitro studies of the secretory behavior of the parietovisceral ganglion in Aplysia californica were performed. The aim of these studies was to investigate the release of polypeptides in response to depolarizing stimuli, and, in particular, to determine if a specific polypeptide known to induce egg laying in the intact animal is secreted into the bathing medium. During continuous perfusion of a ganglion preincubated in leucine-3H the application of either high-potassium medium or a burst of electrical stimuli (via the pleurovisceral connective nerve) evoked a marked increase in the amount of trichloroacetic acid (TCA)-precipitable radioactivity recovered in the perfusate. Enhanced release could be detected within 80 sec of the initial exposure to high potassium; however, incubation of a ganglion in calcium-free media before the application of high-potassium medium abolished the increase of precipitable radioactivity. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of perfusate samples revealed a significant change in the polypeptide species washed from the ganglion during high-potassium depolarization. Bioassays confirmed that egg laying is induced when high-potassium medium used to bathe a ganglion is injected into a recipient animal. These and other results permit the conclusion that the bulk of the polypeptide material secreted from the ganglion in response to depolarization is a specific neurohormone produced by two identified cell clusters, the so-called bag cells.
Ultraviolet-Induced Sensitivity to Visible Light in Ultraviolet Receptors of Limulus
Authors: Nolte John , Brown Joel E.
Published: May 2004

In the UV-sensitive photoreceptors of the median ocellus (UV cells), prolonged depolarizing afterpotentials are seen following a bright UV stimulus. These afterpotentials are abolished by long-wavelength light. During a bright UV stimulus, long-wavelength light elicits a sustained negative-going response. These responses to long-wavelength light are called repolarizing responses. The spectral sensitivity curve for the repolarizing responses peaks at 480 nm; it is the only spectral sensitivity curve for a median ocellus electrical response known to peak at 480 nm. The reversal potentials of the repolarizing response and the depolarizing receptor potential are the same, and change in the same way when the external sodium ion concentration is reduced. We propose that the generation of repolarizing responses involves a thermally stable intermediate of the UV-sensitive photopigment of UV cells.
Changes from High Potassium (HK) to Low Potassium (LK) in Bovine Red Cells
Authors: Israel Yedy , Macdonald Alain , Bernstein Jaime , Rosenmann Eduardo
Published: May 2004

Red cells of newborn calves contain 105–110 mmole K+ and 1–5 mmole Na+ per liter of cells. As the animals age the K+ content decreases to a value of 25–30 mmole/liter of cells after about 60 days. At approximately the same time, the sodium content reaches a value of 60–70 mmole/liter. The time required for half change (t½) is 35–37 days for both Na+ and K+. The activity of (Na + K)-adenosine triphosphatase (ATPase) and the influx of K42 and Rb86 into the red cells are high at birth and are reduced to 5 and 15% of their original values, respectively, in mature animals. t½ for both is of the order of 30–35 days. The membrane Mg-ATPase activity is also high at birth and is reduced with a t½ of 28–32 days to a final value of about 20% of its activity at birth. Separation of red cells according to their age showed that, in animals at the age of transition, newly formed red cells contain a higher K/Na ratio and a higher active transport capacity than older red cells of the same animal. It is suggested that the changes observed are a reflection of the average age of the red cell population as the animal grows.
Ultrastructure within the Lateral Plexus of the Limulus Eye
Authors: Gur Moshe , Purple Richard L. , Whitehead Russell
Published: May 2004

The ultrastructure of the lateral plexus in the compound eye of Limulus is investigated by serial section technique. "Cores" of tissue containing the axons, lateral plexus, and neuropile associated with one sensory ommatidium show the following features: (a) collateral branches from retinular cells do not contribute to the lateral plexus proper, but do form retinular neuropile by contacting collaterals of a self-contained cluster of retinular axons; (b) collateral branches from eccentric cell axons always branch repeatedly upon leaving the parent axon, and compose the bulk of the lateral plexus; (c) the most distal collateral branches from an eccentric cell axon appear to form neuropile and synaptic contacts with each other, whereas more proximal branches form synaptic contacts with collaterals from eccentric cell axons of neighboring ommatidia. We conclude that the ribbon synapses and associated transmitter substance in eccentric cell collaterals must be inhibitory, and that two pathways for self-inhibition may exist. We suggest, as a working hypothesis for the structure of the lateral plexus, a branching pattern with depth that mirrors the horizontal spread of lateral inhibition measured physiologically.
Regulation of Tension in the Skinned Crayfish Muscle Fiber
Authors: Brandt P. W. , Reuben J. P. , Grundfest H.
Published: May 2004

Tension outputs were measured in skinned crayfish muscle fibers exposed to solutions variously buffered for both Mg-adenosine triphosphate (ATP) and Ca. Two types of data are shown, relating tension and substrate concentration with different levels of Ca present, or tension and calcium concentration at different levels of substrate. The data are fitted by curves calculated from a general equation for substrate inhibition. The equation is based on the schema that both tension and relaxation are induced by the substrate and that the relaxing effect of excess substrate is repressed by calcium. The physiological findings of the present work are similar to data obtained by others on biochemical model systems of the contractile proteins.
Ionic Conductances of Extracellular Shunt Pathway in Rabbit Ileum
Authors: Frizzell Raymond A. , Schultz Stanley G.
Published: May 2004

The unidirectional influxes of Na, K, and Cl into isolated strips of rabbit ileum are comprised of movements across the mucosal membrane of the epithelial cells and ionic diffusion into an extracellular shunt pathway. A large fraction of the Na influx across the mucosal membrane alone is inhibited by Li, suggesting the participation of a carrier mechanism in the influx process. The partial ionic shunt conductances of Na, K, and Cl account for at least 82% of the total tissue conductance. The calculated shunt permeabilities (P) are (in centimeters per hour) PK = 0.040, PNa = 0.035, and PCl = 0.019, so that PK:PNa:PCl = 1.14:1.00:0.55. Diffusion potentials across the tissue resulting from isotonic replacement of NaCl in the mucosal solution with mannitol or KCl are described by the Goldman constant-field equation together with the above permeabilities of the shunt pathway. These observations are not consistent with permeation through a fixed-charge pore but can be explained by a model featuring constant ionic partition into a neutral-polar pore that traverses the tight junction. Such a pore may be lined with either fixed dipoles or fixed dipolar ions oriented such that electronegative groups influence the permselective properties of the diffusion pathway. The essential feature of both models is that electroneutrality is maintained by means of fixed membrane components and does not depend upon the presence of mobile counterions.
Active Calcium Ion Uptake by Inside-Out and Right Side-Out Vesicles of Red Blood Cell Membranes
Authors: Weiner Myra L. , Lee Kwang Soo
Published: May 2004

The relationship between active extrusion of Ca++ from red cell ghosts and active uptake of Ca++ by isolated red cell membrane fragments was investigated by studying the Ca++ uptake activities of inside-out and right side-out vesicles. Preparations A and B which had mainly inside-out and right side-out vesicles, respectively, were isolated from red cell membranes and were compared with respect to Ca++ adenosine triphosphatase (ATPase) and ATP-dependent Ca++ uptake activities. Preparation A had nearly eight times more inside-out vesicles and took up eight times more 45Ca in the presence of ATP compared to preparation B. Separation of the 45Ca-labeled membrane vesicles by density gradient centrifugation showed that the 45Ca label was localized to the inside-out vesicle fraction. In addition, the 45Ca taken up in the presence of ATP was lost during a subsequent incubation in the absence of ATP. The rate of 45Ca loss was not influenced by the presence of EGTA, but was slowed in the presence of La+8 (0.1 mM) in the efflux medium. The results presented here support the thesis that the active uptake of Ca++ by red cell membrane fragments is due to the active transport of Ca++ into inside-out vesicles.
The Action of Serotonin on Calcium-45 Efflux from the Anterior Byssal Retractor Muscle of Mytilus edulis
Authors: Bloomquist Eunice , Curtis Brian A.
Published: May 2004

45Ca efflux was studied in resting anterior byssal retractor muscle. The data are described by a three-compartment system. The most rapidly exchanging compartment, with an average time constant of 7 min, contains about 0.9 mM Ca/liter muscle, and probably represents extracellular space. A second compartment, with a time constant of 83 ± 5 min, contains 1.2 mM Ca/liter, and may represent a membrane calcium store. The presence of a third, or more, compartments, probably representing sarcoplasmic reticulum and contractile proteins, is indicated by the fact that the final time constant is 10 times the 83 min time constant of the second compartment. Serotonin (5HT), on initial application, increases 45Ca efflux from this third compartment(s). This effect has a typical dose-response relationship with a maximum response appearing at 10-7 M5HT. In addition, removal of 5HT causes a secondary increase in 45Ca efflux which has a maximum at a 5HT concentration of 10-7 M and declines at both higher and lower doses.
The Permeability of Thin Lipid Membranes to Bromide and Bromine
Authors: Gutknecht John , Bruner L. J. , Tosteson D. C.
Published: May 2004

Thin lipid (optically black) membranes were made from sheep red cell lipids dissolved in n-decane. The flux of Br across these membranes was measured by the use of tracer 82Br. The unidirectional flux of Br (in 50–100 mM NaBr) was 1–3 x 10-12 mole/cm2sec. This flux is more than 1000 times the flux predicted from the membrane electrical resistance (>108 ohm-cm2) and the transference number for Br- (0.2–0.3), which was estimated from measurements of the zero current potential difference. The Br flux was not affected by changes in the potential difference imposed across the membrane (±60 mv) or by the ionic strength of the bathing solutions. However, the addition of a reducing agent, sodium thiosulfate (10-3 M), to the NaBr solution bathing the membrane caused a 90% reduction in the Br flux. The inhibiting effect of S2O3= suggests that the Br flux is due chiefly to traces of Br2 in NaBr solutions. As expected, the addition of Br2 to the NaBr solutions greatly stimulated the Br flux. However, at constant Br2 concentration, the Br flux was also stimulated by increasing the Br- concentration, in spite of the fact that the membrane was virtually impermeable to Br-. Finally, the Br flux appeared to saturate at high Br2 concentrations, and the saturation value was roughly proportional to the Br- concentration. These results can be explained by a model which assumes that Br crosses the membrane only as Br2 but that rapid equilibration of Br between Br2 and Br- occurs in the unstirred layers of aqueous solution bathing the two sides of the membrane. A consequence of the model is that Br- "facilitates" the diffusion of Br across the unstirred layers.
Response of the Frog Skin to Steady-State Voltage Clamping
Authors: Mandel Lazaro J. , Curran Peter F.
Published: May 2004

Properties of the shunt pathway (a pathway in parallel to the Na transport system) in frog skin have been examined. The permeability of this shunt to urea increases markedly when the skin is depolarized to -100 mv (inside negative) but hyperpolarization to +100 mv produces no change in urea permeability compared to short-circuit conditions. The permeability increase at depolarizing potentials is dependent on the external solute concentration and is considerably reduced by the presence of external Ca. Neither urea permeability nor its response to changes in potential difference are affected by complete inhibition of Na transport by ouabain. In ouabain-poisoned skins, movements of Na, K, Cl, and mannitol through the shunt change in parallel with urea movements. Ion fluxes under these conditions and their response to potential can be described by the constant field equation. The selectivity of the shunt is in the order Cl > urea > K > Na > mannitol and this order does not appear to be affected by the absolute magnitude of the shunt permeability. Arguments are presented suggesting that the pathway is mainly between cells and that its permeability may be affected by cell swelling.
The Permeability of the Sodium Channel to Metal Cations in Myelinated Nerve
Authors: Hille Bertil
Published: May 2004

The relative permeability of sodium channels to eight metal cations is studied in myelinated nerve fibers. Ionic currents under voltage-clamp conditions are measured in Na-free solutions containing the test ion. Measured reversal potentials and the Goldman equation are used to calculate the permeability sequence: Na+ ≈ Li+ > Tl+ > K+. The ratio PK/PNa is 1/12. The permeabilities to Rb+, Cs+, Ca++, and Mg++ are too small to measure. The permeability ratios agree with observations on the squid giant axon and show that the reversal potential ENa differs significantly from the Nernst potential for Na+ in normal axons. Opening and closing rates for sodium channels are relatively insensitive to the ionic composition of the bathing medium, implying that gating is a structural property of the channel rather than a result of the movement or accumulation of particular ions around the channel. A previously proposed pore model of the channel accommodates the permeant metal cations in a partly hydrated form. The observed sequence of permeabilities follows the order expected for binding to a high field strength anion in Eisenman's theory of ion exchange equilibria.
Inactivation of the Sodium Current in Myxicola Giant Axons
Authors: Goldman L. , Schauf C. L.
Published: May 2004

Experiments were conducted on Myxicola giant axons to determine if the sodium activation and inactivation processes are coupled or independent. The main experimental approach was to examine the effects of changing test pulses on steady-state inactivation curves. Arguments were presented to show that in the presence of a residual uncompensated series resistance the interpretation of the results depends critically on the manner of conducting the experiment. Analytical and numerical calculations were presented to show that as long as test pulses are confined to an approximately linear negative conductance region of the sodium current-voltage characteristic, unambiguous interpretations can be made. When examined in the manner of Hodgkin and Huxley, inactivation in Myxicola is quantitatively similar to that described by the h variable in squid axons. However, when test pulses were increased along the linear negative region of the sodium current-voltage characteristic, steady-state inactivation curves translate to the right along the voltage axis. The shift in the inactivation curve is a linear function of the ratio of the sodium, conductance of the test pulses, showing a 5.8 mv shift for a twofold increase in conductance. An independent line of evidence indicated that the early rate of development of inactivation is a function of the rise of the sodium conductance.
The Effects of Intracellular Iontophoretic Injection of Calcium and Sodium Ions on the Light Response of Limulus Ventral Photoreceptors
Authors: Lisman J. E. , Brown J. E.
Published: May 2004

During intracellular iontophoretic injection of Ca++ into Limulus ventral photoreceptor cells, there is a progressive diminution of the light response. Following Ca++ injection, the size of the light response slowly recovers. Similarly, there is a progressive diminution of the light response during intracellular injection of Na+ and recovery after the injection is stopped. The rate of diminution during Na+ injection is greater for higher [Ca++]out. In solutions which contain 0.1 mM Ca++, there is nearly no progressive decrease in the size of the light response during Na+ injection. Intracellular injections of Li+ or K+ do not progressively decrease the size of the light response. We propose that an increase in [Na+]in leads to an increase in [Ca++]in and that an increase in [Ca++]in by any means leads to a reduction in responsiveness to light.
Dynamics of Encoding in a Population of Neurons
Authors: Knight Bruce W.
Published: May 2004

A simple encoder model, which is a reasonable idealization from known electrophysiological properties, yields a population in which the variation of the firing rate with time is a perfect replica of the shape of the input stimulus. A population of noise-free encoders which depart even slightly from the simple model yield a very much degraded copy of the input stimulus. The presence of noise improves the performance of such a population. The firing rate of a population of neurons is related to the firing rate of a single member in a subtle way.
Cation Transport in Dog Red Cells
Authors: Romualdez A. , Sha'afi R. I. , Lange Y. , Solomon A. K.
Published: May 2004

Studies have been made on the cation transport system of the dog red cell, a system of particular interest because it has been shown that there is a marked dependence of cation fluxes on the cell volume. We have found that a 10% decrease in cell volume causes a large increase in 1 hr uptake of 24Na as well as a considerable inhibition of 42K uptake. This effect cannot be produced by a difference in medium osmolality but rather requires the cell volume to change. Dog red cell uptake of 24Na is not inhibited by iodoacetate. Phloretin inhibits 24Na uptake and lactate production, and virtually abolishes the volume effect on Na uptake. These several observations may be accounted for in terms of a working hypothesis which presupposes a cation carrier complex which pumps K into and Na out of cells of normal volume. When the cells are shrunken the carrier specificity shifts to an external Na-specific mode and there is a large increase in 24Na uptake, driven by the inwardly directed Na electrochemical potential gradient.
Light Adaptation of Discrete Waves in the Limulus Photoreceptor
Authors: Srebro Richard , Behbehani Mahmood
Published: May 2004

Light adaptation affects discrete waves in two ways. It reduces their average size and decreases the probability that a photon incident at the cornea causes a discrete wave. There is no effect of light adaptation on the latency of discrete waves, or on their time-course.
The Effect of Surface Charge on the Voltage-Dependent Conductance Induced in Thin Lipid Membranes by Monazomycin
Authors: Muller Robert U. , Finkelstein Alan
Published: May 2004

Differences in the behavior of phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) thin lipid membranes treated with monazomycin are shown to be due to the negative surface charge on PG membranes. We demonstrate that shifts of the conductance-voltage (g-V) characteristic of PG films produced by changes of univalent or divalent cation concentrations result from changes of the membrane surface potential on one or both sides. In particular, if divalent cations are added to the aqueous phase not containing monazomycin, the resulting asymmetry of the surface potentials results in an intramembrane potential difference not recordable by electrodes in the bulk phases. Nevertheless, this intramembrane potential difference is "seen" by the monazomycin, and consequently the g-V characteristic is shifted along the voltage axis. These changes are accounted for by diffuse double layer theory. Thus we find it unnecessary to invoke specific binding of Mg++ or Ca++ to the negative charges of PG membranes to explain the observation that concentrations of these ions some 100-fold lower than that of the univalent cation present produce large shifts of the g-V characteristic. We suggest that analogous shifts of g-V characteristics in axons produced by changes of divalent cation concentration are also best explained by diffuse double layer theory.
Phosphate Starvation and the Nonlinear Dynamics of Insect Fibrillar Flight Muscle
Authors: White D. G. S. , Thorson John
Published: May 2004

The nonlinear mechanical dynamics of glycerinated insect fibrillar flight muscle are investigated. The most striking nonlinearity reported previously, which often resulted in oscillatory work being limited to frequencies below those of natural flight, disappears if 5 mM or more orthophosphate is added to the experimental solutions. We show that two further asymmetric nonlinearities, which remain even though phosphate is present, are predicted by cross-bridge theory if one takes account of the expected distortion of attached cross-bridges as filament sliding becomes appreciable. Adenosine triphosphate and adenosine diphosphate have opponent effects upon the mechanical rate constants, suggesting a scheme for the sequential ordering of the events comprising the cross-bridge cycle.
Some Kinetic and Metabolic Characteristics of Calcium-Induced Potassium Transport in Human Red Cells
Authors: Kregenow Floyd M. , Hoffman Joseph F.
Published: May 2004

When fresh human erythrocytes or their ghosts are incubated with Ca + IAA (iodoacetic acid) + adenosine, K permeability increases; K permeability also increases when energy-depleted cells or their ghosts are incubated with Ca alone. Na transport decreases or remains unaltered in both situations. The Ca-induced increase in K permeability in the depleted cell system is qualitatively similar to that seen in the fresh cell system and furnishes a means for studying the metabolic dependence of calcium's action. Studies with the depleted system suggest that the normal refractiveness of the cell to calcium is provided by a metabolically dependent substrate. Removal of this substrate allows Ca to enter the cell and exert its effect. By using 47Ca, a maximum value was obtained (3–7 x 10-6 moles/liter of red blood cells) for the quantity of calcium that is taken up by the cell and responsible for the change in K permeability. Measurements of the unidirectional fluxes of K, obtained during the time Ca increases K permeability, appear to satisfy the flux ratio equation for passive diffusion through a membrane.
Chloride Fluxes in Isolated Dialyzed Barnacle Muscle Fibers
Authors: DiPolo R.
Published: May 2004

Chloride outflux and influx has been studied in single isolated muscle fibers from the giant barnacle under constant internal composition by means of a dialysis perfusion technique. Membrane potential was continually recorded. The chloride outfluxes and influxes were 143 and 144 pmoles/cm2-sec (mean resting potential: 58 mv, temperature: 22°–24°C) with internal and external chloride concentrations of 30 and 541 mM, respectively. The chloride conductance calculated from tracer measurements using constant field assumptions is about fourfold greater than that calculated from published electrical data. Replacing 97% of the external chloride ions by propionate reduces the chloride efflux by 51%. Nitrate ions applied either to the internal or external surface of the membrane slows the chloride efflux. The external pH dependence of the chloride efflux follows the external pH dependence of the membrane conductance, in the range pH 3.9–4.7, increasing with decreasing pH. In the range pH 5–9, the chloride efflux increased with increasing pH, in a manner similar to that observed in frog muscle fibers. The titration curve for internal pH changes in the range 4.0–7.0 was quantitatively much different from that for external pH change, indicating significant asymmetry in the internal and external pH dependence of the chloride efflux.
Mode of Operation of Ampullae of Lorenzini of the Skate, Raja
Authors: Obara S. , Bennett M. V. L.
Published: May 2004

Ampullae of Lorenzini are sensitive electroreceptors. Applied potentials affect receptor cells which transmit synaptically to afferent fibers. Cathodal stimuli in the ampullary lumen sometimes evoke all-or-none "receptor spikes," which are negative-going recorded in the lumen, but more frequently they evoke graded damped oscillations. Cathodal stimuli evoke nerve discharge, usually at stimulus strengths subthreshold for obvious receptor oscillations or spikes. Anodal stimuli decrease any ongoing spontaneous nerve activity. Cathodal stimuli evoke long-lasting depolarizations (generator or postsynaptic potentials) in afferent fibers. Superimposed antidromic spikes are reduced in amplitude, suggesting that the postsynaptic potentials are generated similarly to other excitatory postsynaptic potentials. Anodal stimuli evoke hyperpolarizations of nerves in preparations with tonic activity and in occasional silent preparations; presumably tonic release of excitatory transmitter is decreased. These data are explicable as follows: lumenal faces of receptor cells are tonically (but asynchronously) active generating depolarizing responses. Cathodal stimuli increase this activity, thereby leading to increased depolarization of and increased release of transmitter from serosal faces, which are inexcitable. Anodal stimuli act oppositely. Receptor spikes result from synchronized receptor cell activity. Since cathodal stimuli act directly to hyperpolarize serosal faces, strong cathodal stimuli overcome depolarizing effects of lumenal face activity and are inhibitory. Conversely, strong anodal stimuli depolarize serosal faces, thereby causing release of transmitter, and are excitatory. These properties explain several anomalous features of responses of ampullae of Lorenzini.
Cyclic Adenosine Monophosphate in the Nervous System of Aplysia californica
Authors: Cedar Howard , Kandel Eric R. , Schwartz James H.
Published: May 2004

In the isolated abdominal ganglion of Aplysia, previously incubated in adenine-3H, the amount of 3H-labeled adenosine-3',5' monophosphate (cAMP) doubled after electrical stimulation of nerves at a physiological rate (1/sec). No change was detected after 4 min of stimulation. An increase in cAMP was first seen after 15 min; lengthening the period of stimulation to 1 hr did not increase the extent of the effect. ATP contained 50% of the total radioactivity taken up from adenine-3H, cAMP about 0.1%. During stimulation both the total amount and the specific radioactivity of adenosine triphosphate (ATP) did not change. Thus, the increased amount of radioactivity found in cAMP after stimulation represented an increase in its rate of synthesis. During stimulation formation of cAMP-3H was not altered in nerves or in the cell body of an identified neuron (R2). In addition, no changes were detected in the total amounts of cAMP in the ganglion and in the cell body of R2. It seems likely that the increase was initiated by synaptic activity rather than by action potentials. It was blocked by elevating the concentration of Mg, which also blocks synaptic activity without impairing conduction of impulses. Moreover, impulse activity induced by ouabain and glutamate did not result in increased formation of cAMP.
Cyclic Adenosine Monophosphate in the Nervous System of Aplysia californica
Authors: Cedar Howard , Schwartz James H.
Published: May 2004

Serotonin and dopamine, both likely transmitter substances in Aplysia, stimulated formation of adenosine-3',5' monophosphate (cAMP) in ganglia, connectives, and identified nerve cell bodies. This widespread distribution suggests that receptors for the response are localized throughout the nervous system, as is adenyl cyclase. Both synthesis of cAMP-3H from precursor previously labeled in incubations with adenine-3H and total content of cAMP were stimulated up to 15-fold. The acetylcholine analogue carbachol, glutamate, norepinephrine, and histamine were inactive. Full stimulation occurred within 2–4 min of applying serotonin; the extent of the effect was half maximal at 6µ serotonin. Even in the continued presence of serotonin, the increased cAMP diminished with time. When serotonin was removed, tissue remained refractory for 15–20 min; sensitivity returned after 25 min. Serotonin stimulated cAMP after removal of extracellular Na, K, or Cl and in isotonic sucrose, with all extracellular ions removed. Elevating Mg, which blocked the stimulation of cAMP caused by synaptic activity, did not affect the response to serotonin. Thus the response appeared to be independent of transmitter release and of changes in synaptic potentials and current flow. The role of cAMP in neuronal functioning remains to be determined. Conditions which markedly increased cAMP in neurons, however, did not affect the rate of RNA synthesis, nor did they alter the distribution of phosphorylated adenine or uridine nucleotides.
The Effects of Sodium and Potassium on Ouabain Binding by Human Erythrocytes
Authors: Gardner Jerry D. , Conlon Thomas P.
Published: May 2004

Ouabain binding by the human erythrocyte membrane is reversible, exhibits a high degree of chemical specificity, and can be detected at ouabain concentrations as low as 1 x 10-10M. The relation between ouabain binding and ouabain concentration can be described by a rectangular hyperbola permitting determination of the maximal binding (Bmax) and the ouabain concentration at which ouabain binding is half-maximal (KB). Reducing the external sodium concentration increased KB, while reducing the external potassium concentration decreased KB. Neither cation altered Bmax The reciprocal of KB was a linear function of the sodium concentration at sodium concentrations ranging from 0 to 150 mM. Conversely, the relation between the reciprocal of KB and the external potassium concentration was nonlinear, and raising the potassium concentration above 4 mM produced no further increase in KB. These results are compatible with a model which postulates that the erythrocyte membrane contains a finite number of receptors each composed of a glycoside-binding site and a cation-binding site. When sodium occupies the cation-binding site, the affinity of the glycoside site for ouabain is increased; when potassium occupies the cation-binding site the affinity of the glycoside site for ouabain is decreased.
Effect of Black Widow Spider Venom on the Lobster Neuromuscular Junctions
Authors: Kawai Nobufumi , Mauro Alexander , Grundfest Harry
Published: May 2004

The effect of black widow spider venom (BWSV) on the junctions of the lobster nerve-muscle preparation was studied by intracellular recordings. After application of BWSV both excitatory and inhibitory postsynaptic potentials (epsp and ipsp) were augmented then suppressed. The frequency of miniature potentials was markedly increased by BWSV. Summated postsynaptic conductance changes appeared to be responsible for the membrane depolarization and the decrease in effective membrane resistance seen in the early stages of the venom action. In the later stages both excitatory and inhibitory "giant miniature potentials" were evoked. No discernible changes were found in the reversal potential of the epsp and ipsp and in the sensitivity of the postsynaptic membrane. The results indicate that BWSV has a presynaptic action at crustacean neuromuscular junctions.
Osmotic Regulation of Toad Bladder Responsiveness to Neurohypophyseal Hormones
Authors: Eggena Patrick
Published: May 2004

The effect of dilution of the interstitial fluids on the responsiveness of the toad urinary bladder to antidiuretic hormones has been examined in vivo and in vitro. Toads were given periodic injections with vasopressin while in water so that their plasma osmolality fell below 190 mosmoles/kg H2O. The hydraulic conductivity of bladders which had been removed from the animal and fixed with 1% glutaraldehyde was 10-fold less in overhydrated toads than in normally hydrated controls. A similar inhibitory phenomenon was observed in in vitro studies, when the tonicity of Ringer's fluid in which the bladders were suspended was lowered from its isotonic value. Mannitol, but not urea, could be effectively substituted for one-half of the NaCl content of Ringer's fluid. In other experiments it has been shown that the responsiveness of the bladder to vasotocin is depressed during bulk water movement across the tissue. This "flux inhibition" was found to depend upon the velocity and the duration of water flow from mucosa to the serosa. It is suggested that the responsiveness of the toad bladder to antidiuretic hormones diminishes as the effective osmotic pressure of the interstitial fluids declines.
Adaptation in Skate Photoreceptors
Authors: Dowling John E. , Ripps Harris
Published: May 2004

Receptor potentials were recorded extracellularly from the all-rod retina of the skate after the application of sodium aspartate. This agent suppresses the responses of proximal elements, but leaves relatively unaffected the electrical activity of the photoreceptors (a-wave) and pigment epithelium (c-wave). Since the latter develops too slowly to interfere with the receptor response, it was possible to isolate receptor potentials and to compare their behavior in light and dark adaptation with earlier observations on the S-potential, b-wave, and ganglion cell discharge. The results show that the photoreceptors display the full complement of adaptational changes exhibited by cells proximal to the receptors. Thus, it appears that visual adaptation in the skate is governed primarily by the photoreceptors themselves. Of particular interest was the recovery of sensitivity in the presence of background fields that initially saturate the receptor potential. Analysis of this recovery phase indicates that a gain-control mechanism operates within the receptors, at a distal stage of the visual process.
The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum
Authors: Scarpa Antonio , Baldassare Judith , Inesi Giuseppe
Published: May 2004

X-537 A and A 23187, two antibiotics which form liphophilic complexes with divalent cations, function as ionophores in vesicular fragments of sarcoplasmic reticulum (SR). Addition of either ionophore to SR preloaded with calcium in the presence of adenosine triphosphate (ATP), causes rapid release of calcium. Furthermore, net calcium accumulation by SR is prevented, when the ionophores are added to the reaction mixture before ATP. On the contrary, ATP-independent calcium binding to SR is not inhibited. This effect is specific for the two antibiotics and could not be reproduced, either by inactive derivatives, or by other known ionophores. Neither ionophore produces alterations of the electron microscopic appearance of SR membranes or inhibition of the calcium-dependent ATPase. In fact, the burst of ATP hydrolysis obtained on addition of calcium, is prolonged in the presence of the ionophores. Lanthanum inhibits ATP-independent calcium binding to SR, ATP-dependent calcium accumulation and calcium-dependent ATPase. However, addition of lanthanum to SR preloaded in the presence of ATP, does not cause calcium release. The reported experiments indicated that: (a) ATP-dependent calcium accumulation by SR results in primary formation of calcium ion gradients across the membrane. (b) Most of the accumulated calcium is not available for displacement by lanthanum on the outer surface of the membrane. (c) Calcium ionophores induce rapid equilibration of the gradients, by facilitating cation diffusion across the membrane.
A Study of the Reinnervation of Fast and Slow Mammalian Muscles
Authors: McArdle Joseph J. , Albuquerque Edson X.
Published: May 2004

Miniature end plate potential (mepp) frequency in innervated extensor muscle is significantly higher than in soleus muscle. 9 days after nerve crush mepps of low amplitude and prolonged duration reappeared at a frequency of 2% of control and were similar to normal muscles after 35 days. Membrane potential began to increase 9–10 days after nerve crush and at 30 days was similar to controls. The region most sensitive to ACh in denervated and reinnervated muscles was the end plate. Caffeine (20 mM, 23°C) induced contracture in innervated soleus but not in extensor muscles. After denervation the extensor became sensitive to caffeine while the soleus muscles decreased in sensitivity to the drug; 4–5 days after reinnervation the effect of caffeine on these muscles was similar to control. The events during reinnervation are: (a) reappearance of mepps at the same time as end plate potential and muscle twitch; (b) partial restoration of the membrane potential; (c) return of caffeine-induced contracture to normal levels in the soleus and its absence in the extensor muscles; (d) return of membrane resistance to normal values in both muscles at about 25 days; and (e) return of ACh-sensitivity to control levels at about 30 days in both muscles. Although these results suggest that the membrane potential and sarcoplasmic reticulum are under neural influence, it remains to be established whether or not separate neurotrophic factors are involved.
The Effect of Hypertonic Media on Water Permeability of Frog Urinary Bladder
Authors: Ripoche P. , Bourguet J. , Parisi M.
Published: May 2004

The frog urinary bladder undergoes, in some conditions, a marked increase of its water permeability when incubated in hypertonic media. This increase was observed with various nonpermeant solutes. It seems to result from the shrinkage of an osmo-sensitive compartment of the tissue, probably the epithelial cells. Many similarities were found between this effect and the physiological increase in water permeability (hydrosmotic response) elicited by antidiuretic hormone (ADH): both were dependent on the physiological state of the animals, and although the response was slower after hyperosmolar than after hormonal challenge, the patterns of response were similar, and in both cases markedly dependent on bathing solution temperature. Norepinephrine and prostaglandin E1, which in this tissue reduce the hydrosmotic action of ADH, presumably by inhibiting the adenyl cylase also reduced the effect of hyperosmolarity. Conversely this effect was potentiated by incubation in the presence of oxytocin, exogenous cyclic AMP, and theophylline, conditions in which the intracellular concentration of cyclic AMP is increased. These data demonstrate that the response to hyperosmolarity is elicited, at least partly, by mechanisms also involved in the physiological hydrosmotic response to ADH.