bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Amphotericin B on the Water and Nonelectrolyte Permeability of Thin Lipid Membranes
Authors: Andreoli Thomas E. , Dennis Vincent W. , Weigl Ann M.
Published: May 2004

This paper reports the effects of amphotericin B, a polyene antibiotic, on the water and nonelectrolyte permeability of optically black, thin lipid membranes formed from sheep red blood cell lipids dissolved in decane. The permeability coefficients for the diffusion of water and nonelectrolytes (PDDi) were estimated from unidirectional tracer fluxes when net water flow (Jw) was zero. Alternatively, an osmotic water permeability coefficient (Pf) was computed from Jw when the two aqueous phases contained unequal solute concentrations. In the absence of amphotericin B, when the membrane solutions contained equimolar amounts of cholesterol and phospholipid, Pf was 22.9 ± 4.6 µsec-1 and PDDHDH2O was 10.8 ± 2.4 µsec-1. Furthermore, PDDi was < 0.05 µsec-1 for urea, glycerol, ribose, arabinose, glucose, and sucrose, and σi, the reflection coefficient of each of these solutes was one. When amphotericin B (10-6 M) was present in the aqueous phases and the membrane solutions contained equimolar amounts of cholesterol and phospholipid, PDDHDH2O was 18.1 ± 2.4 µsec-1; Pf was 549 ± 143 µsec-1 when glucose, sucrose, and raffinose were the aqueous solutes. Concomitantly, PDDi varied inversely, and σi directly, with the effective hydrodynamic radii of the solutes tested. These polyene-dependent phenomena required the presence of cholesterol in the membrane solutions. These data were analyzed in terms of restricted diffusion and filtration through uniform right circular cylinders, and were compatible with the hypothesis that the interactions of amphotericin B with membrane-bound cholesterol result in the formation of pores whose equivalent radii are in the range 7 to 10.5 A.
Mechanisms of Accommodation in Different Types of Frog Neurons
Authors: Stoney S. D. , Machne Xenia
Published: May 2004

Responses of individual spinal ganglion neurons, sympathetic ganglion neurons, and motoneurons of frogs to linearly rising currents were investigated utilizing microelectrodes for intracellular stimulation and recording. Spinal ganglion neurons exhibited rapid accommodation to linearly rising currents. Minimal current gradients (MCG's) required to excite these neurons (average value, 106 rheobases/sec) were of the same order of magnitude as for some nerve fibers. Although sympathetic ganglion neurons exhibited responses to lower current gradients than spinal ganglion neurons, distinct MCG's (average value, 26 rheobases/sec) could always be established. MCG's could not be detected in most motoneurons, even with current gradients as low as 0.6 rheobase/sec. A few motoneurons exhibited distinct MCG's (average value, 11 rheobases/sec). The failure of spinal ganglion neurons to respond to anything other than rapidly rising currents appears to be due primarily to the development of severe delayed rectification. The inability of sympathetic ganglion neurons to respond to low current gradients appears to depend not only on delayed rectification but also on increases in depolarization threshold. When present in motoneurons, accommodation appears to result from the same mechanisms responsible for its appearance in sympathetic ganglion neurons.
Volume Control by Muscle Fibers of the Blue Crab
Authors: Lang Michael A. , Gainer Harold
Published: May 2004

Single isolated muscle fibers from the walking legs of the blue crab, Callinectes sapidus act as Boyle-van't Hoff osmometers with an osmotically inactive volume of 33 %. Fibers in hypotonic salines undergo a spontaneous volume readjustment toward the initial volumes of the cells found in isotonic salines. The volume readjustment is initiated by the increase in cell volume in hypotonic salines and appears to be dependent on the duration of exposure of the fiber to external sodium, the sodium concentration, and the pH of the external medium. The volume-readjusted cells continue to behave as osmometers, but with an increased relative osmotically inactive volume and a decreased internal resistivity. The decreases in cell volumes appear to be, in large part, due to losses of osmotically active nonelectrolytes from the cells.
Potassium Fluxes in Dialyzed Squid Axons
Authors: Mullins L. J. , Brinley F. J.
Published: May 2004

Measurements have been made of K influx in squid giant axons under internal solute control by dialysis. With [ATP]i = 1 µM, [Na]i = 0, K influx was 6 ± 0.6 pmole/cm2 sec; an increase to [ATP]i = 4 mM gave an influx of 8 ± 0.5 pmole/cm2 sec, while [ATP]i 4, [Na]i 80 gave a K influx of 19 ± 0.7 pmole/cm2 sec (all measurements at ∼16°C). Strophanthidin (10 µM) in seawater quantitatively abolished the ATP-dependent increase in K influx. The concentration dependence of ATP-dependent K influx on [ATP]i, [Na]i, and [K]o was measured; an [ATP]i of 30 µM gave a K influx about half that at physiological concentrations (2–3 mM). About 7 mM [Na]i yielded half the K influx found at 80 mM [Na]i. The ATP-dependent K influx responded linearly to [K]o from 1–20 mM and was independent of whether Na, Li, or choline was the principal cation of seawater. Substances tested as possible energy sources for the K pump were acetyl phosphate, phosphoarginine, PEP, and d-ATP. None was effective except d-ATP and this substance gave 70% of the maximal flux only when phosphoarginine or PEP was also present.
Proteins of Excitable Membranes
Authors: Nachmansohn David
Published: May 2004

Excitable membranes have the special ability of changing rapidly and reversibly their permeability to ions, thereby controlling the ion movements that carry the electric currents propagating nerve impulses. Acetylcholine (ACh) is the specific signal which is released by excitation and is recognized by a specific protein, the ACh-receptor; it induces a conformational change, triggering off a sequence of reactions resulting in increased permeability. The hydrolysis of ACh by ACh-esterase restores the barrier to ions. The enzymes hydrolyzing and forming ACh and the receptor protein are present in the various types of excitable membranes. Properties of the two proteins directly associated with electrical activity, receptor and esterase, will be described in this and subsequent lectures. ACh-esterase has been shown to be located within the excitable membranes. Potent enzyme inhibitors block electrical activity demonstrating the essential role in this function. The enzyme has been recently crystallized and some protein properties will be described. The monocellular electroplax preparation offers a uniquely favorable material for analyzing the properties of the ACh-receptor and its relation to function. The essential role of the receptor in electrical activity has been demonstrated with specific receptor inhibitors. Recent data show the basically similar role of ACh in the axonal and junctional membranes; the differences of electrical events and pharmacological actions are due to variations of shape, structural organization, and environment.
On Some Structural Analogies between Acetylcholinesterase and the Macromolecular Receptor of Acetylcholine
Authors: Changeux Jean-Pierre , Podleski Thomas , Meunier Jean-Claude
Published: May 2004

Several properties of the enzyme acetylcholinesterase (AChE) isolated in vitro are compared with those of the membrane receptor(s) of acetylcholine expressed by the in vivo electrical response of the electroplax membrane. AChE strongly binds in vitro effectors of the electroplax: agonists e.g., decamethonium or antagonists, e.g., d-tubocurarine and flaxedil. It also reacts covalently with an affinity labeling reagent of the acetylcholine receptor site(s) in vivo (TDF). Two classes of sites on AChE molecule account for the binding of these quaternary nitrogen containing compounds: (1) the anionic site of the active center and (2) noncatalytic "peripheral anionic centers" located outside the active center. A disulfide bond breaking agent, dithiothreitol (DTT) alters in a parallel manner the reaction of AChE and the excitable membrane of the electroplax to TDF. The irreversibility of TDF action is lost in both cases, after exposure to DTT. Both AChE and the acetylcholine receptor thus contain disulfide bonds—they are closely related but not necessarily identical proteins.
Isologous Oxygen, Sulfur, and Selenium Compounds as Probes of Acetylcholine Receptors
Authors: Mautner Henry G.
Published: May 2004

Evidence is presented that while the conformations of acetylcholine and acetylthiolcholine are different, acetylthiolcholine and acetylselenolcholine are structurally and conformationally very similar. Experiments with sulfur and selenium isologs of acetylcholine, choline, and local anesthetics suggest that the active sites of receptors of the electroplax and of electric eel acetylcholinesterase are different, but are compatible with the postulate that acetylcholine receptors of axonal and synaptic excitable membranes are similar.
Ion Transport and the Development of Hydrogen Ion Secretion in the Stomach of the Metamorphosing Bullfrog Tadpole
Authors: Forte John G. , Limlomwongse Liangchai , Kasbekar Dinkar K.
Published: May 2004

Isolated bullfrog tadpole stomachs secrete H+ by stage XXIV of metamorphosis, when tail reabsorption is nearly complete. At this stage the PD shows characteristic responses identical to those of the adult. The appearance of HCl secretion correlates well with other studies showing the morphogenesis of oxyntic cells. Prior to the development of H+ secretion tadpole stomachs maintain a PD similar in polarity and magnitude to that of the adult; i.e., secretory (S) side negative with respect to the nutrient (N) side. The interdependence with aerobic metabolism appeared to increase progressively through metamorphosis; however, glycolytic inhibitors always abolished the PD. Isotopic flux analysis showed that the transepithelial movement of Na+ was consistent with passive diffusion, whereas an active transport of Cl- from N to S was clearly indicated. Variations in [Na+], [K+], and [Cl-] in the bathing solutions induced changes consistent with the following functional description of the pre-H+-secreting tadpole stomach. (a) The S side is relatively permeable to Cl-, but not to Na+ or K+. (b) An equilibrium potential for K+ and Cl- exists at the N interface. (c) Ouabain abolishes the selective K+ permeablity at the N interface and reduces the total PD. (d) Effects of Na+ replacement by choline in the N solution become manifest only below 10–20 mM. It is concluded that prior to development of H+ secretion, the tadpole gastric PD is generated by a Cl- pump from N to S and a Na+ pump operating from the cell interior toward the N side.
Sodium plus Potassium-Activated, Ouabain-Inhibited AdenosineTriphosphatase from a Fraction of Rat Skeletal Muscle, and Lack of Insulin Effect on It
Authors: Rogus Ellen , Price Thomas , Zierler Kenneth L.
Published: May 2004

An ATPase, activated by Na+ plus K+ in the presence of Mg++ and inhibited by ouabain, has been obtained from rat skeletal muscle. Unlike ATPase's with similar properties obtained from other preparations, this ATPase was found only in the fraction containing fragmented sarcoplasmic reticulum. It is suggested that in rat skeletal muscle this ATPase may reside in sarcoplasmic reticulum and not in sarcolemma. This ATPase differed in its pH optimum and in its cation sensitivity from that of rat brain and from that of human muscle reported by Samaha and Gergely (1965, 1966). Because insulin accelerates Na+ efflux from muscle, efforts were made to determine whether or not this effect of insulin could be attributed to increased Na+ + K+-activated ATPase activity. Insulin, administered either in vivo or in vitro, had no demonstrable effect on the enzyme system, nor did it protect against inhibition by ouabain.
Function of Insect Compound Eyes Containing Crystalline Tracts
Authors: Døving Kjell B. , Miller William H.
Published: May 2004

Image formation is studied in compound eyes of insects that contain crystalline tracts. In optical experiments the course of light is studied in fresh scalps of dark-adapted eyes using point and extended sources. In the tract region a point source gives a diffusely lighted area within which are punctate spots about 10 times brighter. Because the position of these spots does not change when the source is moved, and because their spacing agrees with estimates based on the known scalp depth, we conclude that these spots represent light radiating from the cut ends of tracts. An extended source gives a dim erect image in the tract region that may come from the pattern of illumination radiating from the cut ends of the tracts. In electrophysiological experiments intracellular microelectrode recordings of responses to illumination are made from single retinular cells of the skipper, Epargyreus clarus, an animal that lacks iris pigment. Measurements of visual fields of single retinular cells by three methods give half-power beam widths of about 2°. Though not conclusive, these experiments suggest that only the light contained in the tract is effective in stimulating the retinular cell. This agrees with the theoretical study of Allen (1968) and is inconsistent with the superposition theory of Exner (1891) as applied to certain moth and skipper eyes.
The Ventral Photoreceptor Cells of Limulus
Authors: Millecchia Ronald , Mauro Alexander
Published: May 2004

The ventral photoreceptors of Limulus polyphemus are unipolar cells with large, ellipsoidal somas located long both "lateral olfactory nerves." As a consequence of their size and location, the cells are easily impaled with microelectrodes. The cells have an average resting potential of -48 mv. The resting potential is a function of the external concentration of K. When the cell is illuminated, it gives rise to the typical "receptor potential" seen in most invertebrate photoreceptors which consists of a transient phase followed by a maintained phase of depolarization. The amplitude of the transient phase depends on both the state of adaptation of the cell and the intensity of the illumination, while the amplitude of the maintained phase depends only on the intensity of the illumination. The over-all size of the receptor potential depends on the external concentration of Na, e.g. in sodium-free seawater the receptor potential is markedly reduced, but not abolished. On the other hand lowering the Ca concentration produces a marked enhancement of both components of the response, but predominantly of the steady-state component. Slow potential fluctuations are seen in the dark-adapted cell when it is illuminated with a low intensity light. A spike-like regenerative process can be evoked by either the receptor potential or a current applied via a microelectrode. No evidence of impulse activity has been found in the axons of these cells. The ventral photoreceptor cell has many properties in common with a variety of retinular cells and therefore should serve as a convenient model of the primary receptor cell in many invertebrate eyes.
Two Components of the Cardiac Action Potential
Authors: de Carvalho Antonio Paes , Hoffman Brian Francis , de Paula Carvalho Marilene
Published: May 2004

Transmembrane potentials recorded from the rabbit heart in vitro were displayed as voltage against time (V, t display), and dV/dt against voltage (V, V or phase-plane display). Acetylcholine was applied to the recording site by means of a hydraulic system. Results showed that (a) differences in time course of action potential upstroke can be explained in terms of the relative magnitude of fast and slow phases of depolarization; (b) acetylcholine is capable of depressing the slow phase of depolarization as well as the plateau of the action potential; and (c) action potentials from nodal (SA and AV) cells seem to lack the initial fast phase. These results were construed to support a two-component hypothesis for cardiac electrogenesis. The hypothesis states that cardiac action potentials are composed of two distinct and physiologically separable "components" which result from discrete mechanisms. An initial fast component is a sodium spike similar to that of squid nerve. The slow component, which accounts for both a slow depolarization during phase 0 and the plateau, probably is dependent on the properties of a slow inward current having a positive equilibrium potential, coupled to a decrease in the resting potassium conductance. According to the hypothesis, SA and AV nodal action potentials are due entirely or almost entirely to the slow component and can therefore be expected to exhibit unique electrophysiological and pharmacological properties.
Membrane Characteristics of the Canine Papillary Muscle Fiber
Authors: Sakamoto Yasuzi
Published: May 2004

Passive and active responses to intracellular and extracellular stimulation were studied in the canine papillary muscle. The electrotonic potential produced by extracellular polarization with the partition chamber method fitted the time course and the spatial decay expected from the cable theory (the time constant, 3.3 msec; the space constant, 1.2 mm). Contrariwise, spatial decay of the electrotonic potentials produced by intracellular polarization was very short and did not fit the decay curve expected for a simple cable, although only a small difference of time course in the electrotonic potentials produced by intracellular and extracellular polarizations was observed. A similar time course might result from the fact that when current flow results from intracellular polarization, the input resistance is less dependent on the membrane resistance. The foot of the propagated action potential rose exponentially with a time constant of 1.1 msec and a conduction velocity of 0.68 m/sec. The membrane capacity was calculated from the time constant of the foot potential and the conduction velocity to be 0.76 µF/cm2. The responses of the papillary muscle membrane to intracellular stimulation differed from those to extracellular stimulation applied with the partition method in the following ways: higher threshold potential, shorter latency for the active response, linearity of the current-voltage relationship, and no reduction in the membrane resistance at the crest of the action potential during current flow.
The Intracellular Site of Calcium Activation of Contraction in Frog Skeletal Muscle
Authors: Winegrad Saul
Published: May 2004

Radioautography has been used to localize 45Ca in isotopically labeled frog skeletal muscle fibers which had been quickly frozen during a maintained tetanus, a declining tetanus, or during the period immediately following a tetanus or a contracture. During a tetanus almost all of the myofibrillar 45Ca is localized in the region of the sarcomere occupied by the thin filaments. The amount varies with the tension being developed by the muscle. The movement of calcium within the reticulum from the tubular portion to the terminal cisternae during the posttetanic period has a half-time of about 9 sec at room temperature and a Q10 of about 1.7. Repolarization is not necessary for this movement. Evidence is given to support the notion that most calcium efflux from the cell occurs from the terminal cisternae into the transverse tubules.
The Coupling of Solute Fluxes in Membranes
Authors: Galey William R. , Van Bruggen J. T.
Published: May 2004

Our previous description of solute drag on a synthetic membrane has been extended to include the solutes mannitol, sucrose, raffinose, inulin, and dextran. Labeled and nonlabeled forms of these solutes were used in pairs to quantitate solute flux interaction. Three membranes with pore sizes of 350, 80, and 20 A, respectively, have been utilized. It is shown that solute flux interaction occurs with all the solutes and that the extent of interaction is related directly to solute permeability, concentration, and molecular size. The magnitude of solute interaction is reciprocally related to the radii of the membrane pores, greater interaction occurring with small pored membranes. Solute drag is seen as an increased flux of tracer solute in the direction of the diffusion gradient of a second solute as well as a decreased tracer flux into the diffusion gradient. Values are given for self-diffusion and interaction coefficients as well as for a new coefficient, the "effectiveness coefficient."
Fractionation of Sodium Efflux in Frog Sartorius Muscles by Strophanthidin and Removal of External Sodium
Authors: Horowicz P. , Taylor J. W. , Waggoner D. M.
Published: May 2004

The influence of strophanthidin, ouabain, and the removal of external sodium on the sodium efflux from frog sartorius muscle was measured. In freshly dissected muscles strophanthidin and ouabain in maximally effective concentrations reduced the efflux of sodium by about 50%. Of the sodium efflux which is strophanthidin-insensitive about 75% is inhibited after complete replacement of external sodium by lithium. In the absence of strophanthidin replacement of external sodium by lithium, calcium, or magnesium produces an initial rise in the sodium efflux, followed by a fall in the efflux as the exposure of the muscles to sodium-free media is continued. When the muscles are exposed for prolonged periods in sodium-free media, the fraction of internal sodium lost per minute is higher when returned to normal Ringer fluid than it was initially. The activation of sodium efflux by external sodium after long periods in sodium-free solutions is partly strophanthidin-sensitive and partly strophanthidin-insensitive. The internal sodium concentration is an important factor in these effects. The effects of temperature on the sodium efflux were also measured. Above 7°C the Q10 of both the strophanthidin-sensitive and strophanthidin-insensitive sodium efflux is about 2.0. Below 7°C the strophanthidin-insensitive sodium efflux has a Q10 of about 7.4.
Ionic Channels and Nerve Membrane Lipids Cholesterol-tetrodotoxin interaction
Authors: Villegas Raimundo , Barnola Flor V. , Camejo Germáan
Published: May 2004

Experiments were carried out to investigate possible interactions of tetrodotoxin (TTX) with lipid molecules isolated from nerve fiber plasma membranes of the squid Dosidicus gigas. TTX has a highly selective ability to block the channel normally used by Na+ to cross the axolemma during nervous impulse conduction. In order to investigate the interaction each lipid sample was spread on 5 x 10-7 M TTX and TTX-free 0.15 M NaCl solutions adjusted to pH 7.4 with 7 x 10-3 M phosphate buffer. The surface pressure-area diagrams of the lipid monolayers revealed that TTX interacts only with cholesterol. The expansion of the cholesterol monolayers at 5 x 10-7 M TTX was 2 A2/molecule at zero pressure for the experiments at 20°C and 2.5 A2/molecule for those at 25°C. Similar results were obtained in KCl subphases. The apparent dissociation constant of the cholesterol-TTX complex calculated from dose-response experiments is 2.6 x 10-7 M. Experiments at pH 10.1 revealed that the zwitter ionic form of TTX is less active. Experiments with cholesterol derivatives (cholesteryl acetate, cholesterol methyl ether, cholestanol, and cholestanyl acetate) indicate that for the interaction with TTX a partial negatively charged group at C-3 and a double bond between C-5 and C-6 on the steroid nucleus are required. Tetrodonic acid, a biologically inactive derivative of TTX, does not interact with cholesterol. The results lead us to propose that cholesterol is part of the Na+ channel.
Amphibian Lens Histones and Their Relation to the Cell Cycle
Authors: Johnson Alan , Rothstein Howard
Published: May 2004

Histones have been electrophoretically separated from acid extracts of the frog lens for the first time. The five conventional histone fractions, representing four electrophoretic bands (f1; f2b, f3; f2a2; and f2a1), are present in both the epithelial and fiber cells. In addition, a fifth fraction was isolated from both sources and the evidence suggests that it may be a tissue-specific histone, possibly related to the lysine-rich f2c fraction found previously only in nucleated erythrocytes. The epithelial cells contain a substantially greater amount of histone than the fiber cells. Moreover, the fibers, unlike the epithelium, manifest no net histone synthesis or turnover following lenticular explantation. Microspectrophotometric, radioautographic, and gel electrophoretic studies indicate that the histones are synthesized in frog lenses concurrently with DNA. Inhibition of DNA synthesis does not completely abolish that of histones but reduces it by about one-half. In the early stages of culture (prior to their synthesis and that of DNA) the histones appear to undergo alterations which are prevented by treatment with cycloheximide.
Studies on the Mechanism of Interferon Action
Authors: Friedman Robert M.
Published: May 2004

Interferon does not inactivate viruses or viral RNA. Virus growth is inhibited in interferon-treated cells, but apart from conferring resistance to virus growth, no other effect of interferon on cells has been definitely shown to take place. Interferon binds to cells even in the cold, but a period of incubation at 37°C is required for development of antiviral activity. Cytoplasmic uptake of interferon has not been unequivocally demonstrated. Studies with antimetabolites indicate that the antiviral action of interferon requires host RNA and protein synthesis. Experiments with 2-mercapto-1(ß-4-pyridethyl) benzimidazole (MPB) suggest that an additional step is required between the binding and the synthesis of macromolecules. Interferon does not affect the adsorption, penetration, or uncoating of RNA or DNA viruses, but viral RNA synthesis is inhibited in cells infected with RNA viruses. The main action of interferon appears to be the inhibition of the translation of virus genetic information probably by inhibiting the initiation of virus protein synthesis.
Circulating Interferon Production in the Mouse
Authors: De Maeyer Edward , De Maeyer-Guignard Jaqueline , Jullien Pierre
Published: May 2004

A radiobiological study of circulating interferon production in the mouse was undertaken in the hope of elucidating the site(s) of circulating interferon production. After total body X-irradiation of the animals, different radiosensitivities of circulating interferon production were observed with different viral inducers. Myxovirus-induced circulating interferon production was especially radiosensitive. Moreover, a study of interferon production in syngeneic and xenogeneic radiochimeras demonstrated that cells producing NDV (Newcastle disease virus)-induced circulating interferon were derived from hematopoietic stem cells. In addition, treatment of mice with antilymphocyte serum significantly reduced NDV- and Sendai virus-induced circulating interferon, as opposed to other inducers. Taken together, these results strongly suggest that the lymphocyte is the major source of myxovirus-induced circulating interferon. A survey of interferon production in 12 inbred mouse strains, using NDV as inducer, revealed the existence of low and high producers. A Mendelian analysis carried out with low producing Balb/c and high producing C57BL indicated that the difference between low and high interferon producers was caused by a single, autosomal, codominant factor.
Direct Measurement of Uptake of Sodium at the Outer Surface of the Frog Skin
Authors: Biber Thomas U. L. , Curran Peter F.
Published: May 2004

A combination of the methods described by Schultz et al. (6) and by Ussing and Zerahn (9) was used to measure directly the unidirectional uptake of sodium from the outside solution into the frog skin, under short-circuit conditions. The sodium uptake was determined at six sodium concentrations ranging from 3.4 to 114 mM. NaCl was replaced by choline chloride in the solutions bathing both sides of the skin. Sodium uptake is not a linear function of sodium concentration but appears to be composed of two components, a saturating one and one that varies linearly with concentration. The sodium uptake is inhibited by the addition of lithium to the outside solution. The effect appears to be primarily on the saturating component and has the characteristics of competitive inhibition. In addition, lithium uptake by the skin is inhibited by sodium. The effects of lithium cannot be ascribed to changes in electrical potential difference. Measurements with microelectrodes indicate that under short-circuit condition there is no change in the intracellular potential when lithium chloride is added to the outside solution.
Specific Uncoupling of Excitation and Contraction in Mammalian Cardiac Tissue by Lanthanum
Authors: Sanborn W. G. , Langer G. A.
Published: May 2004

Arterially cannulated rabbit interventricular septal tissue was exposed to 5–40 µM La in 2.5 mM Ca perfusate. Immediately following perfusion with La two concurrent events were consistently observed: (a) a rapid decline of active tension to a lesser steady-state value, and (b) an abrupt, release of short duration of tissue-bound Ca. The magnitude of both events was directly related to the [La]o. If the duration of exposure to La was brief, contractility returned toward normal upon return to the La-free perfusate. Elevation of [Ca]o during exposure to La counteracted its effect and induced a concurrent displacement of tissue-bound La. Cellular action potentials recorded during brief perfusion with La demonstrated that essentially normal regenerative depolarization was maintained. Analysis of the quantities of 45Ca released following exposure to 10 µM La indicated that this La-susceptible Ca was being displaced from a homogeneous pool—the one previously shown by Langer to represent contractile dependent Ca. These data led to the following conclusions: During perfusion with 2.5 mM Ca contractile dependent Ca was derived primarily from "superficially" located sites. La effected the release of contractile dependent Ca by modifying the normal permselectivity of this "superficial" membrane for activator Ca. These and other data infer that contractile dependent Ca is derived primarily from superficially located sites.
Threshold and Receptor Reserve in the Action of Neurohypophyseal Peptides
Authors: Eggena Patrick , Schwartz Irving L. , Walter Roderich
Published: May 2004

The interrelationship of several physiological receptors which influence the hydroosmotic response of the toad urinary bladder was studied employing neurohypophyseal peptides, prostaglandin E1, theophylline, and cyclic nucleotides. The binding property of agonists (pD2), synergists (pS2), competitive antagonists (pA2), and noncompetitive antagonists (pD2') was determined after a suitable methodology had been developed. A series of neurohypophyseal peptides was examined in detail for their catalytic activity. It was found that the replacement of the hydroxy radical of the tyrosine residue in oxytocin by a methoxy and then by an ethoxy radical led to a progressive decline in the catalytic activity of the hormone—corresponding to a change from agonist to partial agonist to competitive antagonist. [4-Leucine]-mesotocin behaved as a competitive antagonist of oxytocin. Prostaglandin E1 (PGE1) was found to be a noncompetitive inhibitor of neurohypophyseal peptides and theophylline; whereas the maximal hydroosmotic response of the bladder to [2-O-methyltyrosine]-oxytocin and theophylline was greatly depressed by PGE1, the response to saturating concentrations of oxytocin was only slightly diminished—a finding which reveals a "receptor reserve" for oxytocin. Saturating concentrations of [2-O-ethyltyrosine]-oxytocin, inactive per se, potentiate theophylline—disclosing a "threshold phenomenon" for the mediation of neurohypophyseal hormone action. It is concluded that neurohypophyseal peptides are capable of producing graded effects on adenyl cyclase both below and above the range of enzyme activity which evokes graded changes in membrane permeability.
Influence of Polyvalent Cations on the Activation of Muscle End Plate Receptors
Authors: Lambert Donald H. , Parsons Rodney L.
Published: May 2004

The influence of polyvalent cations on the activation of end plate receptors has been studied in vitro on the sartorius muscle of the frog. In the absence of extracellular calcium, the sensitivity of the receptors to depolarizing quaternary ammonium salts was markedly reduced. Maximum receptor activation occurred in those fibers equilibrated in 1.8 mM calcium Ringer solution, with the response being reduced as the calcium concentration was raised or lowered. Magnesium was less efficient than calcium in regulating the sensitivity of the end plate receptors, the maximum receptor response occurring in those fibers equilibrated in 8 mM magnesium Ringer solution. In the presence of lanthanum the end plate response to carbamylcholine or acetylcholine was enhanced. Lanthanum increased the conductance change produced by carbamylcholine both in polarized and in potassium-depolarized fibers. The application of 10-2 mM lanthanum to the end plate increased MEPP's amplitude, rise time, and half-fall time by 19, 54, and 45%, respectively. The results suggest that polyvalent cations influence postjunctional membrane receptor processes in addition to their well-documented prejunctional action.
Regulatory Mechanisms of the Calcium Transport System of Fragmented Rabbit Sarcoplasmic Reticulum
Authors: Weber A.
Published: May 2004

The rate of ATP hydrolysis decreases very rapidly during the first 2 sec of calcium uptake. It changes with time in a manner similar to that described for calcium net uptake by other workers, suggesting that the two activities are coupled. The decline in both rates may be ascribed to an inhibitory effect of accumulated calcium on calcium influx and ATPase activity for the following reasons. During the steady state, Ca-Ca and Sr-Ca exchange and the rate of ATP hydrolysis are much slower than the initial rate of net calcium uptake and the associated ATP hydrolysis. If the accumulation of free calcium is prevented by calcium-oxalate precipitation the initial rate of net calcium uptake does not decay during prolonged periods of transport. Furthermore, passive preloading of vesicles with calcium inhibits the rate of hydrolysis in proportion to the extent of preloading. The inhibition of steady-state flux is alleviated by free ATP; i.e., not chelated with magnesium, but not by free ITP.
Spectral Sensitivity of the Barnacle, Balanus amphitrite
Authors: Stratten Wilford P. , Ogden Thomas E.
Published: May 2004

The extracellular ocellar potential was used to evaluate the spectral sensitivity of the ocellus of the barnacle, Balanus amphitrite. Maximum relative sensitivity was at 530–540 nm. Studies with chromatic adapting lights suggest that the receptors contain a single photopigment. The spectra were relatively broader in the dark as compared to the light-adapted state. This effect was shown to be due to an increase in the slope of the amplitude-intensity function, caused by light adaptation. Studies of tapetal fluorescence and corneal transmission indicate little effect of the ocellar media on the determination of sensitivity.
Potassium and Sodium Transport across Single Distal Tubules of Amphiuma
Authors: Wiederholt M. , Sullivan W. J. , Giebisch G.
Published: May 2004

The transport properties of potassium (K) and sodium (Na) were studied in single distal tubules of Amphiuma using free-flow micropuncture techniques and stationary microperfusion methods. The transepithelial movement of labeled potassium was measured utilizing a three-compartment system in series in which the time course of tracer disappearance from the lumen was followed. Under control conditions, in blood- and doubly-perfused kidneys, extensive active net reabsorption of sodium and potassium obtains along single distal tubules. Tubular potassium reabsorption is abolished by ouabain at a concentration of 5 x 10-6 M. Significant net secretion of K can be induced by exposing Amphiuma to a high K environment (100 mM KCl) or by adding acetazoleamide (1 x 10-4 M) to the perfusion fluid. Transepithelial movement of potassium involves mixing with only a small fraction of total distal tubular cell potassium. This transport pool of potassium increases significantly with the transition from tubular net reabsorption to net secretion. Indirect evidence is presented which indicates that increased active K uptake across the peritubular cell boundary may be of prime importance during states of net K secretion.
The Effect of Valinomycin on the Electrical Properties of Solutions of Red Cell Lipids in n-Decane
Authors: Andreoli Thomas E. , Tosteson Daniel C.
Published: May 2004

This paper reports the electrical properties of thick lipid membranes in the absence and presence of valinomycin. The thick lipid membranes were formed by placing a solution of sheep red cell lipids in decane between two cellophane partitions which formed the interfaces between the membrane and the two aqueous bathing solutions. The DC electrical resistance of these structures was found to be directly proportional to the reciprocal of the concentration of lipids in the decane (CL). The limiting resistance, as (CL-1) approached zero, was 3 x 108 ohm-cm2. Resistance was also found to be linearly related to membrane thickness. The limiting resistance at zero thickness was again 1–3 x 108 ohm-cm2. These data are interpreted to indicate that the DC resistance of thick lipid membranes comprises two surface resistances (RS) at each interface with the aqueous bathing solutions, and a bulk resistance (RB) of the lipid-decane solution, arranged in series. Measurements of the effect of variations of area on resistance were consistent with this interpretation. Valinomycin reduced RS but had no effect on RB. Under certain conditions, thick lipid membranes containing valinomycin behaved like highly selective K+ electrodes.
Effect of Geometrical and Chemical Constraints on Water Flux across Artificial Membranes
Authors: Gary-Bobo C. M. , Solomon A. K.
Published: May 2004

Studies have been made on the temperature dependence of both the hydraulic conductivity, Lp, and the THO diffusion coefficient, ω, for a series of cellulose acetate membranes (CA) of varying porosity. A similar study was also made of a much less polar cellulose triacetate membrane (CTA). The apparent activation energies, Ea, for diffusion across CA membranes vary with porosity, being 7.8 kcal/mole for the nonporous membrane and 5.5 kcal/mole for the most porous one. Ea for diffusion across the less polar CTA membrane is smaller than Ea for the CA membrane of equivalent porosity. Classical viscous flow, in which the hydraulic conductivity is inversely related to bulk water viscosity, has been demonstrated across membranes with very small equivalent pores. Water-membrane interactions, which depend upon both chemical and geometrical factors are of particular importance in diffusion. The implication of these findings for the interpretation of water permeability experiments across biological membranes is discussed.
Divalent Ions and the Surface Potential of Charged Phospholipid Membranes
Authors: McLaughlin S. G. A. , Szabo G. , Eisenman G.
Published: May 2004

Phospholipid bilayer membranes were bathed in a decimolar solution of monovalent ions, and the conductance produced by neutral carriers of these monovalent cations and anions was used to assess the electric potential at the surface of the membrane. When the bilayers were formed from a neutral lipid, phosphatidylethanolamine, the addition of alkaline earth cations produced no detectable surface potential, indicating that little or no binding occurs to the polar head group with these ions. When the bilayers were formed from a negatively charged lipid, phosphatidylserine, the addition of Sr and Ba decreased the magnitude of the surface potential as predicted by the theory of the diffuse double layer. In particular, the potential decreased 27 mv for a 10-fold increase in concentration in the millimolar-decimolar range. A 10-fold increase in the Ca or Mg concentration also produced a 27 mv decrease in potential in this region, which was again due to screening, but it was necessary to invoke some specific binding to account for the observation that these cations were effective at a lower concentration than Ba or Sr. It is suggested that the ability of the alkaline earth cations to shift the conductance-voltage curves of a nerve along the voltage axis by 20–26 mv for a 10-fold increase in concentration may be due to essentially a screening rather than a binding phenomenon.
Conductance Change Associated with Receptor Potentials of Gustatory Cells in Rat
Authors: Ozeki Masahiro
Published: May 2004

The electrical properties of gustatory cells and cells which do not respond to chemical stimuli in the taste bud of fungiform papillae in rats were studied by means of intracellular microelectrodes. Neither of these cell types showed spike electrogenesis. Gustatory cells showed a depolarization, the receptor potential, associated with an increase in the membrane conductance in response to NaCl, sucrose, and HCl, whereas quinine produced a decrease in the conductance together with an increase in the receptor potential magnitude. The reversal point of the receptor potential in response to NaCl or KCl was close to zero membrane potential, but in the case of quinine it was at a more negative potential level than the resting potential. From these results two receptive processes are postulated in the gustatory cell membrane. When the gustatory cells were stimulated for a long duration by concentrated NaCl or sucrose, receptor potentials showed adaptation with decrease in magnitude, but adaptation of the responses to HCl and quinine were hardly detected. Adaptation of the receptor potential was not correlated with conductance change.
Ionic Channels and Nerve Membrane Constituents
Authors: Villegas Raimundo , Barnola Flor V.
Published: May 2004

Saxitoxin (STX) and tetrodotoxin (TTX) have the same striking property of blocking the Na+ channels in the axolemma. Experiments with nerve plasma membrane components of the squid Dosidicus gigas have shown that TTX interacts with cholesterol monolayers. Similar experiments were carried out with STX. The effect of STX on the surface pressure-area diagrams of lipid monolayers and on the fluorescence emission spectra of sonicated nerve membranes was studied. The results indicate a TTX-like interaction of STX with cholesterol monolayers. The expansion of the monolayers caused by 10-6 M STX was 2.2 A2/cholesterol molecule at 25°C. From surface pressure measurements at constant cholesterol area (39 A2/molecule) in media with various STX concentrations, it was calculated that the STX/cholesterol surface concentration ratio is 0.54. The apparent dissociation constant of the STX-cholesterol monolayer complex is 4.0 x 10-7 M. The STX/cholesterol ratio and the apparent dissociation constant are similar to those determined for TTX. The presence of other lipids in the monolayers affects the STX-cholesterol association. The interactions of STX and TTX with cholesterol monolayers suggest (a) that cholesterol molecules may be part of the nerve membrane Na+ channels, or (b) that the toxin receptor at the nerve membrane shares similar chemical features with the cholesterol monolayers.
Energetics of Sodium Transport in Frog Skin
Authors: Vieira F. L. , Caplan S. R. , Essig A.
Published: May 2004

Sodium transport and oxygen consumption were studied simultaneously in the short-circuited frog skin. Sodium transport was evaluated from Io/F, where Io is the short-circuit current measured with standard Ringer's solution bathing each surface and F is the Faraday constant. Oxygen tension was measured polarographically. Under a variety of circumstances the rate of oxygen consumption from the outer solution exceeded that from the inner solution, the ratio being constant (0.57 ± 0.09 SD). Both Io and the associated rate of oxygen consumption Jro declined nonlinearly with time, but the relationship between them was linear, suggesting that the basal oxygen consumption was constant. For each skin numerous experimental points were fitted by the best straight line. The intercept (Jro)Io=0 then gave the basal oxygen consumption, and the slope dNa/dO2 gave an apparent stoichiometric ratio for a given skin. The basal oxygen consumption was about one-half the total oxygen consumption in a representative untreated short-circuited skin. Values of dNa/dO2 in 10 skins varied significantly, ranging from 7.1 to 30.9 (as compared with Zerahn's and Leaf and Renshaw's values of about 18). KCN abolished both Io and Jro. 2,4-dinitrophenol (DNP) depressed Io while increasing Jro four- to fivefold. Anti-diuretic hormone stimulated and ouabain depressed both Io and Jro; in both cases apparent stoichiometric ratios were preserved.
The Effects of Temperature on the Labellar Chemoreceptors of the Blowfly
Authors: Uehara S. , Morita H.
Published: May 2004

In the labellar chemosensory hairs of the blowfly, Phormia regina Meigen, stationary amplitudes of the slow potentials induced by salt and sugar stimulations were decreased to 50–80% at 12°C of the values measured at 28°C. The amplitudes induced by water did not show any dependence on temperature change. The maximum rate of rise of the receptor potentials was strongly increased with rising temperature. The value of Kb, the apparent Michaelis constant, was less by a factor of six at 28°C compared to the 12°C value for the sugar receptor.
Dual Sensitivities of Cells in Wolf Spider Eyes at Ultraviolet and Visible Wavelengths of Light
Authors: DeVoe Robert D.
Published: May 2004

Intracellular recordings have been made from visual cells in principal and secondary eyes of in vitro wolf spider preparations. The responses of all cells to all wavelengths of light were graded depolarizations; no hyperpolarizations or nerve discharges were seen. Cells in a secondary eye, the anterior lateral eye, had a maximum sensitivity in the visible at 510 nm and a secondary maximum, or shoulder, of sensitivity in the near ultraviolet at 380 nm. Cells in principal eyes, the anterior median eyes, all responded maximally both in the visible at 510 nm and in the ultraviolet at 360–370 nm or less. However, there was no typical ratio of ultraviolet to visible sensitivities; the differences in log sensitivities (log UV/VIS) varied from 3.3 to -0.5. Each principal eye had a population of cells with different ratios. These populations varied with the time of the year, possibly due to changes in light upon the animals. Chromatic adaptations of cells in anterior median (but not anterior lateral) eyes resulted in small, selective changes in spectral sensitivities, and there was some facilitation of responses from cells repeatedly stimulated. It is concluded that cells of secondary eyes contain only a visual pigment absorbing maximally in the visible, while cells of principal eyes probably contain variable amounts of both this pigment and one absorbing in the ultraviolet as well.
A Theoretical Analysis of the Capacitance of Muscle Fibers Using a Distributed Model of the Tubular System
Authors: Eisenberg R. S. , Vaughan P. C. , Howell J. N.
Published: May 2004

A model is developed to predict the changes in total capacitance (i.e. total charge stored divided by surface membrane potential) of the tubular system of muscle fibers. The tubular system is represented as a punctated disc and the area of membrane across which current flows is represented as a punctated annulus, the capacitance of the muscle fiber being proportional to this area. The area can be determined from a distributed model of the tubular system, in which the only resistance to radial current flow is presumed to be in the lumen of the tubules. Calculations are made of the variation of capacitance expected as the conductivity of the bathing solution is varied. These calculations include the effects of fixed charge in the tubular lumen and the effects of changes in the shape and volume of the tubular system in solutions of low conductivity. The calculated results fail to fit comparable experimental data, although they do qualitatively account for the known variation of the radial spread of contraction with conductivity of the bathing medium. It is pointed out that the existence of a significant "access resistance" at the mouth of the tubules might explain the discrepancy between theory and experiment.