bluuebunny/crossref_metadata_2025 huggingface dataset:
The Subcellular Origin of Bioluminescence in Noctiluca miliaris
Authors: Eckert Roger , Reynolds George T.
Published: May 2004

The light emitted by Noctiluca has its origin in 1 to 5 x 104 organelles ("microsources") which are scattered throughout the perivacuolar cytoplasm, and which appear to be the elementary functional units of bioluminescence. Microscopical techniques, image intensification, and microphotometry were employed in their investigation. Microsources are fluorescent, strongly phase-retarding, and range widely in diameter below 1.5 microns. The number of quanta emitted in a flash from a microsource ("microflash") is of the order of 105 photons. However, microflashes show a wide range of intensities, which are correlated with the size of the organelles from which they arise. Each organelle responds repetitively and with reproducible time course to a succession of invading triggering potentials. Reversible changes in the intensity of the flash emitted by the whole cell ("macroflash") occur because of graduations in intensity of microflashes rather than as a result of changes in the number of responsive organelles. The shape of the flash emitted by individual microsources resembles that of the macroflash except for slightly shorter rise and decay times. It is concluded that the macroflash results from somewhat asynchronous, but otherwise parallel summation of microflashes.
Evidence from Insect Fibrillar Muscle about the Elementary Contractile Process
Authors: Pringle J. W. S.
Published: May 2004

Bundles of myofibrils prepared from the dorsal longitudinal flight muscles of giant water bugs show oscillatory contractile activity in solutions of low ionic strength containing ATP and 10-8-10-7 M Ca2+. This is due to delay between changes of length and changes of tension under activating conditions. The peculiarities of insect fibrillar muscle which give rise to this behavior are (1) the high elasticity of relaxed myofibrils, (2) a smaller degree of Ca2+ activation of ATPase activity in unstretched myofibrils and extracted actomyosin, and (3) a direct effect of stretch on ATPase activity. It is shown that the cross-bridges of striated muscle are probably formed from the heads of three myosin molecules and that in insect fibrillar muscle the cycles of mechanochemical energy conversion in the cross-bridges can be synchronized by imposed changes of length. This material is more suitable than vertebrate striated muscle for a study of the nature of the elementary contractile process.
Temperature Effects on Pacemaker Generation, Membrane Potential, and Critical Firing Threshold in Aplysia Neurons
Authors: Carpenter David O.
Published: May 2004

Temperature increases cause a regular and reproducible increase in the frequency of generation of pacemaker potentials in most Aplysia neurons specialized for this type of activity which can only be explained as a direct stimulating effect of temperature upon the ionic mechanisms responsible for pacemaker potentials. At the same time all cells in the visceral ganglion undergo a membrane potential hyperpolarization of approximately 1–2 mv/°C warmed. In spite of the marked variation in resting membrane potential the critical firing threshold remains at a constant membrane potential level at all temperatures in the absence of accommodative changes. The temperature-frequency curves of all types of cells are interpreted as a result of the interaction between the effects of temperature on the pacemaker-generating mechanism and resting membrane potential. Previous observations on the effects of temperature on excitability of mammalian neurons suggest that other types of neurons may undergo similar marked shifts in resting membrane potential with temperature variation.
Cation Regulation in the Smooth Muscle of Frog Stomach
Authors: Stephenson Elizabeth W.
Published: May 2004

Cation composition of frog smooth muscle cells was investigated. Fresh stomach muscle rings resembled skeletal muscle, but marked Na gain and K loss followed immersion. Mean Na (49.8–79.7 mM/kg tissue) and K (61.8–80.1 mM/kg tissue) varied between batches, but were stable for long periods in vitro. Exchange of 6–30 mM Na/kg tissue with 22Na was extremely slow and distinct. Extracellular water was estimated from sucrose-14C uptake. Calculated exchangeable intracellular Na was 9 mM/kg cell water, and varied little. Thus steady-state transmembrane cation gradients appeared to be steep. K-free solution had only slight effects. Ouabain (10-4 M) caused marked Na gain and reciprocal K loss; at 30°C, Na and K varied linearly with time over a wide range of contents, indicating constant net fluxes. Net fluxes decreased with temperature decrease. 22Na exchange in ouabain-treated tissue at 20–30°C was rapid and difficult to analyze. The best minimum estimates of unidirectional Na fluxes at 30°C were 10–12 times the constant net flux; constant pump efflux may explain these findings. The rapidity of Na exchange may not reflect very high permeability, but it does require a high rate of transport work.
Oxygen Poisoning in Drosophila
Authors: Fenn Wallace O. , Henning Marcia , Philpott Mary
Published: May 2004

Fruit flies live longer at the partial pressure of oxygen found in air than at either larger or smaller partial pressures. Flies exposed to 1 atm of oxygen for 8 hr every day do not recover completely in the remaining 16 hr. In general, intermittent exposures to 1 atm of oxygen are better tolerated than continuous exposure to the same average oxygen concentration per day, but exposures to higher pressures of 2–5 atm of oxygen for as little as a half hour every two days markedly shorten the life-span. Older flies consume more oxygen per minute and are more sensitive to oxygen poisoning than young flies, and the rate of dying in 6 atm of O2, or the reciprocal of the survival time, is a linear function of the age. The oxygen pressure-time curve can be well expressed by the general empirical equation (POO2)2 x time = 120 where P is in atmosphere and survival time in hours. The progress of oxygen poisoning appears to be linear with time rather than exponential.
Variations of the Contractile Apparatus in Smooth and Striated Muscles
Authors: Elliott G. F.
Published: May 2004

Structural information is presented for three muscle systems—mammalian smooth muscle at rest and partially active, living toad striated muscle at rest and contracting, and glycerinated rabbit psoas muscle under various conditions of pH and ionic environment. In the smooth muscle no evidence of organized myosin filaments has been found. In the striated muscle the myosin-to-actin distance can vary widely, according to sarcomere length and to muscle treatment, both at rest and during contraction. In the discussion it is suggested that muscle should be considered as a colloidal system and that there need not necessarily be any chemical bonding (cross-linking) involved in the contractile process.
The Formation and Properties of Thin Lipid Membranes from HK and LK Sheep Red Cell Lipids
Authors: Andreoli Thomas E. , Bangham J. Andrew , Tosteson Daniel C.
Published: May 2004

Lipids were obtained from high potassium (HK) and low potassium (LK) sheep red cells by sequential extraction of the erythrocytes with isopropanol-chloroform, chloroform-methanol-0.1 M KCl, and chloroform. The extract contained cholesterol and phospholipid in a molar ratio of 0.8:1.0, and less than 1% protein contaminant. Stable thin lipid membranes separating two aqueous compartments were formed from an erythrocyte lipid-hydrocarbon solution, and had an electrical resistance of ∼108 ohm-cm2 and a capacitance of 0.38–0.4 µf/cm2. From the capacitance values, membrane thickness was estimated to be 46–132 A, depending on the assumed value for the dielectric constant (2.0–4.5). Membrane voltage was recorded in the presence of ionic (NaCl and/or KCl) concentration gradients in the solutions bathing the membrane. The permeability of the membrane to Na+, K+, and Cl- (expressed as the transference number, Tion) was computed from the steady-state membrane voltage and the activity ratio of the ions in the compartments bathing the membrane. TNa and TK were approximately equal (∼0.8) and considerably greater than TCl (∼0.2). The ionic transference numbers were independent of temperature, the hydrocarbon solvent, the osmolarity of the solutions bathing the membranes, and the cholesterol content of the membranes, over the range 21–38°C. The high degree of membrane cation selectivity was tentatively attributed to the negatively charged phospholipids (phosphatidylethanolamine and phosphatidylserine) present in the lipid extract.
The Equivalent Circuit of Single Crab Muscle Fibers As Determined by Impedance Measurements with Intracellular Electrodes
Authors: Eisenberg Robert S.
Published: May 2004

The input impedance of muscle fibers of the crab was determined with microelectrodes over the frequency range 1 cps to 10 kc/sec. Care was taken to analyze, reduce, and correct for capacitive artifact. One dimensional cable theory was used to determine the properties of the equivalent circuit of the membrane admittance, and the errors introduced by the neglect of the three dimensional spread of current are discussed. In seven fibers the equivalent circuit of an element of the membrane admittance must contain a DC path and two capacitances, each in series with a resistance. In two fibers, the element of membrane admittance could be described by one capacitance in parallel with a resistance. In several fibers there was evidence for a third very large capacitance. The values of the elements of the equivalent circuit depend on which of several equivalent circuits is chosen. The circuit (with a minimum number of elements) that was considered most reasonably consistent with the anatomy of the fiber has two branches in parallel: one branch having a resistance Re in series with a capacitance Ce; the other branch having a resistance Rb in series with a parallel combination of a resistance Rm and a capacitance Cm. The average circuit values (seven fibers) for this model, treating the fiber as a cylinder of sarcolemma without infoldings or tubular invaginations, are Re = 21 ohm cm2; Ce = 47 µf/cm2; Rb = 10.2 ohm cm2; Rm = 173 ohm cm2; Cm = 9.0 µf/cm2. The relation of this equivalent circuit and another with a nonminimum number of circuit elements to the fine structure of crab muscle is discussed. In the above equivalent circuit Rm and Cm are attributed to the sarcolemma; Re and Ce, to the sarcotubular system; and Rb, to the amorphous material found around crab fibers. Estimates of actual surface area of the sarcolemma and sarcotubular system permit the average circuit values to be expressed in terms of unit membrane area. The values so expressed are consistent with the dielectric properties of predominantly lipid membranes.
Structural Aspects of Saltatory Particle Movement
Authors: Rebhun Lionel I.
Published: May 2004

A variety of cells possess particles which show movements statistically different from Brownian movements. They are characterized by discontinuous jumps of 2–30 µ at velocities of 0.5–5 µ/sec or more. A detailed analysis of these saltatory, jumplike movements makes it most likely that they are caused by transmission of force to the particles by a fiber system in the cell outside of the particle itself. Work with isolated droplets of cytoplasm from algae demonstrates a set of fibers involved in both cytoplasmic streaming and saltatory motion, suggesting that both phenomena are related to the same force-generating set of fibers. Analysis of a variety of systems in which streaming and/or saltatory movement occurs reveals two types of fiber systems spatially correlated with the movement, microtubules and 50 A microfilaments. The fibers in Nitella (alga) are of the microfilament type. In other systems (melanocyte processes, mitotic apparatus, nerve axons) microtubules occur. A suggestion is made, based on work on cilia, that a microtubule-microfilament complex may be present in those cases in which only microtubules appear to be present, with the microfilament closely associated with or buried in the microtubule wall. If so, then microfilaments, structurally similar to smooth muscle filaments, may be a force-generating element in a very wide variety of saltatory and streaming phenomena.
Morphological Aspects of Ciliary Motility
Authors: Satir Peter
Published: May 2004

In Elliptio complanatus lateral cilia, two distinct patterns of filament termination can be discerned. In one case, all nine filaments are present and all are single; in the second, at least one filament is missing but doublets are still present. These probably represent different configurations within one cilium in different stroke positions; to get from one to the other, some peripheral filaments must move with respect to others. The data are consistent with the hypothesis that the filaments themselves do not change length, but rather slide past one another to accommodate increasing curvature. The bent regions of the cilium are in the form of circular arcs. In a few cases, apparent displacement of filaments at the tip (Δl) can be shown to be accounted for if we assume that all differences are generated within these arcs. The displacement per degree of bend is 35 A. Regions of bent arc are initially confined to the base of the cilium but move up the shaft as straight regions appear below them. From the relationship between arc length and radius of curvature, a shaft length that is the unit that initially bends and slides may be defined. Quantal displacements of the length of one 14S dynein may perhaps occur at sites between filaments at opposite sides of such a unit as sliding occurs.
Myosin
Authors: Dreizen Paul , Gershman Lewis C. , Trotta Paul P. , Stracher Alfred
Published: May 2004

There is fairly general agreement that myosin isolated from rabbit skeletal muscle has a molecular weight of about 500,000. The higher values that have been reported apparently reflect protein aggregation related to the method of preparation. On the basis of present evidence, the myosin molecule has an elongate helical core of two f subunits (average weight about 215,000) that extend into a globular head region containing three g subunits (average weight about 20,000). Myosin may be dissociated into subunits by a number of methods. In 5 M guanidine, the myosin molecule is dissociated into f and g subunits, while at pH above 10, the g subunits are dissociated from the intact fibrous core of myosin. The dissociation of g subunits at pH 10 is accompanied by the loss of both ATPase activity and actin-binding capacity; however, the exact biological significance of the g subunits is presently uncertain. In preliminary studies, the f subunits appear to contain the sulfhydryl residues currently implicated in myosin ATPase, and there is some indication of allosteric regulation of enzymic activity.
In Vivo Effect of Uncoupling Agents on the Incorporation of Calcium and Strontium into Mitochondria and Other Subcellular Fractions of Rat Liver
Authors: Carafoli E.
Published: May 2004

After injection of 45Ca++ or 89Sr++ into rats, the largest part of the radioactivity in the liver cell is associated with the subcellular structures, only negligible amounts of it being found in the soluble hyaloplasm. 50 % or more of the 45Ca++ and 89Sr++ in the liver cell is recovered in the mitochondrial fraction. The specific activity of Ca++ after injection of 45Ca++ is far greater in mitochondria than in microsomes. Pretreatment of the rats with uncouplers of oxidative phosphorylation markedly decreases the amount of radioactivity associated with the mitochondrial fraction. The amount of radioactivity recovered in the microsomes and in the final supernatant on the contrary increases. These effects are present only when mitochondrial oxidative phosphorylation is completely uncoupled. The Ca++ content of mitochondria from the livers of rats pretreated with uncouplers is sharply decreased with respect to the controls. It is concluded that in the liver cells of the intact animal energy-linked movements of Ca++ and Sr++ take place in mitochondria.
Junctional Membrane Uncoupling
Authors: Loewenstein W. R. , Nakas M. , Socolar S. J.
Published: May 2004

The permeability of the membrane surfaces where cells are in contact (junctional membranes) in Chironomus salivary glands depends on Ca++ and Mg++. When the concentration of these ions at the junctional membranes is raised sufficiently, these normally highly permeable membranes seal off; their permeability falls one to three orders, as they approach the nonjunctional membranes in conductance. This permeability transformation is achieved in three ways: (a) by iontophoresis of Ca++ into the cell; (b) by entry of Ca++ and/or Mg++ from the extracellular fluid into the cell through leaks in the cell surface membrane (e.g., injury); or (c) by entry of these ions through leaks arising, probably primarily in the perijunctional insulation, due to trypsin digestion, anisotonicity, alkalinity, or chelation. Ca++ and Mg++ appear to have three roles in the junctional coupling processes: (a) in the permeability of the junctional membranes; (b) in the permeability of the perijunctional insulation; and (c) a role long known— in the mechanical stability of the cell junction. The two latter roles may well be closely interdependent, but the first is clearly independent of the others.
The Ultrastructural Route of Fluid Transport in Rabbit Gall Bladder
Authors: Tormey John McD. , Diamond Jared M.
Published: May 2004

The route of fluid transport across the wall of the rabbit gall bladder has been examined by combined physiological and morphological techniques. Fluid transport was either made maximal or was inhibited by one of six physiological methods (metabolic inhibition with cyanide-iodoacetate, addition of ouabain, application of adverse osmotic gradients, low temperature, replacement of Cl by SO4, or replacement of NaCl by sucrose). Then the organ was rapidly fixed and subsequently embedded, sectioned, and examined by light and electron microscopy. The structure of the gall bladder is presented with the aid of electron micrographs, and changes in structure are described and quantitated. The most significant morphological feature seems to be long, narrow, complex channels between adjacent epithelial cells; these spaces are closed by tight junctions at the luminal surface of the epithelium but are open at the basal surface. They are dilated when maximal fluid transport occurs, but are collapsed under all the conditions which inhibit transport. Additional observations and experiments make it possible to conclude that this dilation is the result of fluid transport through the spaces. Evidently NaCl is constantly pumped from the epithelial cells into the spaces, making them hypertonic, so that water follows osmotically. It is suggested that these spaces may represent a "standing-gradient flow system," in which osmotic equilibration takes place progressively along the length of a long channel.
Ion Effects on Calcium Accumulation by Cardiac Sarcoplasmic Reticulum
Authors: Palmer Roger F. , Posey Virginia A.
Published: May 2004

The effects of monovalent cations on the active calcium-accumulating ability of cardiac sarcoplasmic reticulum were assessed. Grana prepared in an ion-free system accumulated calcium when ATP and Mg++ were present. Sodium ion and to a lesser extent lithium but not K+ reduced the amount of calcium taken up. The reduction of calcium binding by Na+ is not due to inhibition of uptake but to a rapid release of the radiocalcium bound. The amount of calcium released by sodium does not appear to be enough to explain contraction on the basis of sodium influx into muscle, but may be significant in the regulation of tension.
The Na+, K+, and Cl- Content of Goose Salt Gland Slices and the Effects of Acetylcholine and Ouabain
Authors: Hokin Mabel R.
Published: May 2004

In goose salt gland slices incubated in bicarbonate-buffered medium which contained 170 mEq of Na+/liter, net total tissue Na+, expressed as milliequivalents per kilogram, was, in the presence of either acetylcholine (plus eserine) or ouabain, significantly higher than that of the bathing fluid. Acetylcholine caused an increase in the tissue Na+ content as compared with untreated slices; there was an approximately equivalent decrease in K+ and a significant decrease in Cl-. The calculated net intracellular concentrations of Na+, expressed as milliequivalents per liter of intracellular water, in unstimulated, acetylcholine-stimulated, and ouabain-treated slices were 2.1, 3.1, and 2.7 times higher, respectively, than the concentration of Na+ in the bathing fluid. The net intracellular concentration of Na+, expressed as milliequivalents per liter of intracellular water, in slices incubated in the presence of acetylcholine was 531 mEq/liter; this is approximately the same as the concentration of Na+ in the secreted fluid of the goose salt gland (515 mEq/liter). The results indicate that the main concentration gradient for Na+ could be established across the basal membrane. The data do not indicate whether this involves active transport of Na+ per se. A second stage which might involve Na-K ATPase activity at the luminal membrane is discussed. The sum of the total tissue Na+ and K+ was approximately 250 mEq/kg, whereas the Cl- content was only approximately 130 mEq/kg.
Nature of the Schwann Cell Electrical Potential
Authors: Villegas Jorge , Villegas Raimundo , Giménez Máximo
Published: May 2004

The effects on the Schwann cell electrical potential of external ionic concentrations and of K-strophanthoside were investigated. Increasing (K)o depolarized the cell. The potential is related to the logarithm of (K)o in a quasi-linear fashion. The linear portion of the curve has a slope of 45 mv/ten-fold change in (K)o. Diminutions of (Na)o and (Cl)o produced only small variations in the potential. Calcium and magnesium can be replaced by 44 mM calcium without altering the potential. Increase of (Ca)o to 88 mM produced about 10 mv hyperpolarization. The cell was hyperpolarized by 11 mv and 4 mv within 1 min after applying K-strophanthoside at concentrations of 10-3 and 10-5 M, respectively. No variations of cellular potassium, sodium, or chloride were observed 3 min after applying the glycoside. The hyperpolarization caused by 10-3 M K-strophanthoside was not observed when (K)o was diminished to 1 or 0.1 mM or was increased to 30 mM. At a (K)o of 30 mM, 10-2 M strophanthoside was required to produce the hyperpolarizing effect. In high calcium, the cell was further hyperpolarized by the glycoside. The initial hyperpolarization caused by the glycoside was followed by a gradual depolarization and a decrease of the cellular potassium concentration. The results indicate that the Schwann cell potential of about -40 mv is due to ionic diffusion, mainly of potassium, and to a cardiac glycoside-sensitive ion transport process.
Excitation-Contraction Coupling in a Barnacle Muscle Fiber As Examined with Voltage Clamp Technique
Authors: Hagiwara S. , Takahashi K. , Junge D.
Published: May 2004

Relations between the membrane potential and the tension associated with changes in membrane potential were analyzed in barnacle giant muscle fibers by using voltage clamp techniques. With a step change in membrane potential the tension reaches its final level with a time course which is expressed by the difference of two exponential functions. The time constants τ1 (0.2–0.4 sec at 23°C) and τ2 (0.07–0.12 sec at 23°C) are independent of the new membrane potential at least for a relatively small membrane potential change while the final level of tension is a function of the potential. Decreasing the temperature increases both τ1 and τ2 (Q10 = -2 to -3) and the increase of the tonicity of the external medium increases τ1 but not τ2. The final level of tension is related by an S-shaped curve to the membrane potential. The slope of the final tension-membrane potential curve increases with increasing external Ca concentration and is reduced when a small amount of transition metal ions is added to the medium. This suggests that the influx of Ca ions through the membrane is an important factor in the development of tension.
Charges and Potentials at the Nerve Surface
Authors: Hille Bertil
Published: May 2004

The voltage dependence of the voltage clamp responses of myelinated nerve fibers depends on the concentration of divalent cations and of hydrogen ions in the bathing medium. In general, increases of the [Ca], [Ni], or [H] increase the depolarization needed to elicit a given response of the nerve. An e-fold increase of the [Ca] produces the following shifts of the voltage dependence of the parameters in the Hodgkin-Huxley model: m∞, 8.7 mv; h∞, 6.5 mv; τn, 0.0 mv. The same increase of the [H], if done below pH 5.5, produces the following shifts: m∞, 13.5 mv; h∞, 13.5 mv; τn, 13.5 mv; and if done above pH 5.5: m∞, 1.3 mv; h∞, 1.3 mv; τn, 4.0 mv. The voltage shifts are proportional to the logarithm of the concentration of the divalent ions and of the hydrogen ion. The observed voltage shifts are interpreted as evidence for negative fixed charges near the sodium and potassium channels. The charged groups are assumed to comprise several types, of varying affinity for divalent and hydrogen ions. The charges near the sodium channels differ from those near the potassium channels. As the pH is lowered below pH 6, the maximum sodium conductance decreases quickly and reversibly in a manner that suggests that the protonation of an acidic group with a pKa of 5.2 blocks individual sodium channels.
Oscillations of Potential in the Electroretinogram of the Lobster
Authors: Wald George
Published: May 2004

The electroretinogram (ERG) evoked in the lobster by a short flash of light consists of a highly damped, slow oscillation of potential, triggered apparently by a single excitatory process. Near the threshold, only one wave may be evident; but as the intensity of stimulus rises, a prior wave appears, and grows so much more rapidly as to become dominant. Simultaneously third and later waves appear, so that at high intensities the response may include five to seven waves. Dark adaptation favors the second and later waves relative to the first; light adaptation tends to suppress them. On turning on a steady light the oscillations are superimposed on the early stages of development of a maintained, steady-state potential (on-response). Turning off the light causes a rapid fluctuation of potential followed by a similarly damped slow oscillation (off-response). These phenomena resemble in part oscillations recently observed in the b wave of the ERG of many vertebrates including man.
Action of Certain Tropine Esters on Voltage-Clamped Lobster Axon
Authors: Blaustein M. P.
Published: May 2004

Tropine p-tolylacetate (TPTA) and its quaternary analogue, tropine p-tolylacetate methiodide (TPTA MeI) decrease the early transient (Na) and late (K) currents in the voltage-clamped lobster giant axon. These agents, which block the nerve action potential, reduce the maximum Na and K conductance increases associated with membrane depolarization. They also slow the rate at which the sodium conductance is increased and shift the (normalized) membrane conductance vs. voltage curves in the direction of depolarization along the voltage axis. All these effects are qualitatively similar to those resulting from the action of procaine on the voltage-clamped axon. One unusual effect of the tropine esters, noticeable particularly at large depolarization steps, is that they cause the late, K current to reach a peak and then fall off with increasing pulse duration. This effect has not been reported to occur as a result of procaine action. Tropine p-chlorophenyl acetate (TPClϕA), which differs from TPTA only by the substitution of a p-Cl for a p-CH3 group on the benzene ring, had a negligible effect on axonal excitability.
The Ionic Permeability Changes during Acetylcholine-Induced Responses of Aplysia Ganglion Cells
Authors: Sato Makoto , Austin George , Yai Hideko , Maruhashi Juro
Published: May 2004

ACh-induced depolarization (D response) in D cells markedly decreases as the external Na+ is reduced. However, when Na+ is completely replaced with Mg++, the D response remains unchanged. When Na+ is replaced with Tris(hydroxymethyl)aminomethane, the D response completely disappears, except for a slight decrease in membrane resistance. ACh-induced hyperpolarization (H response) in H cells is markedly depressed as the external Cl- is reduced. Frequently, the reversal of the H response; i.e., depolarization, is observed during perfusion with Cl--free media. In cells which show both D and H responses superimposed, it was possible to separate these responses from each other by perfusing the cells with either Na+-free or Cl--free Ringer's solution. High [K+]0 often caused a marked hyperpolarization in either D or H cells. This is due to the primary effect of high [K+]0 on the presynaptic inhibitory fibers. The removal of this inhibitory afferent interference by applying Nembutal readily disclosed the predicted K+ depolarization. In perfusates containing normal [Na+]0, the effects of Ca++ and Mg++ on the activities of postsynaptic membrane were minimal, supporting the current theory that the effects of these ions on the synaptic transmission are mainly presynaptic. The possible mechanism of the hyperpolarization produced by simultaneous perfusion with both high [K+]0 and ACh in certain H cells is explained quantitatively under the assumption that ACh induces exclusively an increase in Cl- permeability of the H membrane.
The Dynamic Properties of Mammalian Skeletal Muscle
Authors: Bahler Alan S. , Fales John T. , Zierler Kenneth L.
Published: May 2004

The dynamic characteristics of the rat gracilis anticus muscle at 17.5°C have been determined by isotonic and isometric loading. For a fixed initial length these characteristics were represented either as a family of length-velocity phase trajectories at various isotonic afterloads or as a series of force-velocity curves at different lengths. An alternate method of viewing these data, the length-external load-velocity phase space, was also generated. When the muscle was allowed to shorten from different initial lengths, the velocity of shortening achieved at a given length was lower for longer initial lengths. The amount of departure was also dependent upon the isotonic load, the greater the load the greater the departure. The departures were not caused by changes in the elastic elements of the muscle or fatigue in the ordinary sense. When the behavior of the muscle was investigated at different frequencies of stimulation, the shortening velocity was a function of the number of stimulating pulses received by the muscle at a given frequency. The shortening velocity of the rat gracilis anticus muscle is, therefore, not only a function of load and length, but also of an additional variable related to the time elapsed from onset of stimulation.
Sodium and Potassium Fluxes in Isolated Barnacle Muscle Fibers
Authors: Brinley F. J.
Published: May 2004

Sodium and potassium influxes and outfluxes have been studied in single isolated muscle fibers from the giant barnacle both by microinjection and by external loading. The sodium influxes and outfluxes were 49 and 39 pmoles /cm2-sec (temperature = 15–16°C) respectively. The potassium influxes and outfluxes were 28 and 60 pmoles/cm2-sec (temperature = 13–16°C) respectively. Replacement of external sodium by lithium reduced sodium outflux by 67% but had no effect on potassium outflux. Removal of external potassum reduced the sodium outflux by 51% but had no effect on potassium outflux. External strophanthidin (10–30 µM) reduced sodium outflux by 80–90% and increased potassium outflux by 40% in normal fibers. The time constant for sodium exchange increased linearly with internal sodium concentration, as did the fraction of sodium outflux insensitive to a maximally inhibitory concentration of external strophanthidin in the range of 10 tO 80 mM internal sodium. The strophanthidin-sensitive component of sodium outflux could be related to the internal sodium concentration by the following empirical formula:

See PDF for Equation
On the Origin of the Bioelectrical Potential Generated by the Freshwater Clam Mantle
Authors: Istin Michel , Kirschner Leonard B.
Published: May 2004

Mantles from freshwater clams develop potential differences (PD's) between the two surfaces when they are bathed in vitro with artificial saline solutions. The magnitude and polarity of the PD is dependent on [Ca2+] in the solution bathing the mantle's shell surface. When the solutions are gassed with 5% CO2 in oxygen, the PD is in the range 25 to 50 mv, shell side positive. It decreases if [Ca2+] in the shell solution is elevated. The concentration dependence is logarithmic with a slope of about -27 mv per 10-fold change in [Ca2+], slightly less than predicted by the Nernst equation for a membrane acting as a calcium electrode. Analysis of the electrical behavior both in intact mantles and in isolated epithelia indicates that most of the PD develops across the external membranes of epithelial cells on the shell side. There is no evidence that an active calcium transport system is involved in electrogenesis, and a model based on calcium diffusion across a selectively permeable membrane can explain existent data. If CO2 is absent, the mantle PD is very small (2–10 mv), but still sensitive to change in external [Ca2+]. It is proposed that CO2 alters intracellular pH, thereby changing the equilibrium between a large store of nonionized calcium and [Ca2+] in the cells. A role for carbonic anhydrase in the CO2 effect is suggested by the action of a specific inhibitor of this enzyme. The diffusion model predicts that increasing ionized calcium should increase the PD as is actually observed. Some implications of this system for the physiology of calcium movement in vivo are discussed.
Afferent Stochastic Modulation of Crayfish Caudal Photoreceptor Units
Authors: Hermann Howard T. , Olsen Richard E.
Published: May 2004

When all roots to the sixth ganglion of the crayfish are cut, the caudal photoreceptor unit (PRU) fires at regular intervals. With an intact preparation, stimulation of caudal tactile hairs has predominantly inhibitory effects on the PRU: short bursts of afferent impulses, produced by momentary mechanical stimulation of tactile hairs, have (a) occasional immediate excitatory effect on the PRU, (b) prolonged inhibitory effect. The mean firing rate of the afferented and deafferented PRUs reacts similarly to a step increase in light, but the same unit fires faster after deafferentation. In the dark, deafferented units often fire paired or multiple pulses; the interval between pulses in a pair is similar to the short mode in afferented histograms. A fiber-optic probe of the caudal ganglion demonstrates the approximate location of the photosensitive element.
The Roles of Sodium and Potassium Ions in the Generation of the Electro-Olfactogram
Authors: Takagi Sadayuki F. , Wyse Gordon A. , Kitamura Harunobu , Ito Katsuhiro
Published: May 2004

In order to clarify whether or not the electronegative olfactory mucosal potentials (EOG) are generator potentials, the effects of changed ionic enviroment were studied. The EOG decreased in amplitude and in some cases nearly or completely disappeared, when Na+ in the bathing Ringer solution was replaced by sucrose, Li+, choline+, tetraethylammonium+ (TEA), or hydrazine. In the K+-free Ringer solution, the negative EOG's initially increased and then decreased in amplitude. In Ringer's solution with increased K+, the negative EOG's increased in amplitude. When K+ was increased in exchange for Na+ in Ringer's solution, the negative EOG's decreased, disappeared, and then reversed their polarity (Fig. 6). Next, when the K+ was replaced by equimolar sucrose, Li+, choline+, TEA+, hydrazine, or Na+, the reversed potentials recovered completely only in Na+-Ringer's solution, but never in the other solutions. Thus, the essential role of Na+ and K+ in the negative EOG's was demonstrated. Ba++ was found to depress selectively the electropositive EOG, but it hardly decreased and never increased the negative EOG. Hence, it is concluded that Ba++ interferes only with Cl- influx, and that the negative EOG's are elicited by an increase in permeability of the olfactory receptive membrane to Na+ and K+, but not to Cl-. From the ionic mechanism it is inferred that the negative EOG's are in most cases composites of generator and positive potentials.
The Site of Calcium Binding in Relation to the Activation of Myofibrillar Contraction
Authors: Fuchs Franklin , Briggs F. Norman
Published: May 2004

Skeletal muscle myofibrils, in the presence of 2 mM MgCl2 at pH 7.0, were found to have two classes of calcium-binding sites with apparent affinity constants of 2.1 x 106 M-1 (class 1) and ∼3 x 104 M-1 (class 2), respectively. At free calcium concentrations essential for the activation of myofibrillar contraction (∼10-6 M) there would be significant calcium binding only to the class 1 sites. These sites could bind about 1.3 µmoles of calcium per g protein. Extraction of myosin from the myofibrils did not alter their calcium-binding parameters. Myosin A, under identical experimental conditions, had little affinity for calcium. The class 1 sites are, therefore, presumed to be located in the I filaments. The class 1 sites could only be detected in F actin and myosin B preparations which were contaminated with the tropomyosin-troponin complex. Tropomyosin bound very little calcium. Troponin, which in conjunction with tropomyosin confers calcium sensitivity on actomyosin systems, could bind 22 µmoles of calcium per g protein with an apparent affinity constant of 2.4 x 106 M-1. In view of the identical affinity constants of the myofibrils and troponin and the much greater number of calcium-binding sites on troponin it is suggested that calcium activates myofibrillar contraction by binding to the troponin molecule.
Spectral Sensitivity of the Common Prawn, Palaemonetes vulgaris
Authors: Wald George , Seldin Edward B.
Published: May 2004

The vision of Palaemonetes is of particular interest in view of extensive studies of the responses of its chromatophore systems and eye pigments to light. The spectral sensitivity is here examined under conditions of dark adaptation and adaptation to bright colored lights. In each case the relative number of photons per one-fiftieth sec flash needed to evoke a constant peak amplitude (usually 25 or 50 µv) in the electroretinogram (ERG) was measured at various wavelengths throughout the spectrum. The sensitivity is the reciprocal of this number. In dark-adapted animals the spectral sensitivity curve consists of a broad, almost symmetrical band, maximal at about 540 mµ, with a shoulder near 390 mµ. Adaptation to bright red or blue light, left on continuously throughout the measurements, depresses the 540 mµ peak without notably changing its shape or position, implying that only one visual pigment operates in this region. Adaptation to red light, however, spares a violet-sensitive system, so that a high, narrow peak at 390 mµ now dominates the spectral sensitivity function. The 540 and 390 mµ peaks are apparently associated with different visual pigments; and these seem to be segregated in different receptor systems, since the associated ERG's have markedly different time constants. It is suggested that these two sensitivity bands may represent the red- and violet-sensitive components of an apparatus for color differentiation.
A Contribution of an Electrogenic Na+ Pump to Membrane Potential in Aplysia Neurons
Authors: Carpenter David O. , Alving Barbara O.
Published: May 2004

The resting membrane potential (RMP) of Aplysia neurons is very temperature-dependent, and in some cells increases with increasing temperature by as much as 2 mv/°C. RMP at room temperature may significantly exceed the potassium equilibrium potential, which can be determined by measurement of the equilibrium point of the spike after potential. The hyperpolarization on warming is completely abolished by ouabain, replacement of external Na+ by Li+, removal of external K+, and by prolonged exposure to high Ca++, while it is independent of external chloride but is increased by cocaine (3 x 10-3 M). In an identified cell that shows a marked temperature dependence of RMP, both the potassium equilibrium potential and the membrane resistance were found to be relatively independent of temperature. The hyperpolarization on warming, which may increase RMP by as much as 50%, can most reasonably be ascribed to the activity of an electrogenic Na+ pump.
Alteration by Xylocaine (Lidocaine) and Its Derivatives of the Time Course of the End Plate Potential
Authors: Steinbach A. B.
Published: May 2004

Xylocaine and its derivatives act specifically at the neuromuscular junction within the concentration range 0.05 to 2.0 mM. The charged form is the active form of the drugs. There is no correlation between "local anesthetic" activity and effect at the junction. Like d-tubocurarine, these drugs have little or no effect on quantum content, acetylcholinesterase activity, or the passive impedance of the muscle fiber. Yet they produce end plate potentials characterized by a brief, early component and a late, greatly prolonged component, as does procaine. Analysis of these changes in time course suggests that the drugs have little or no effect before receptors are activated by acetylcholine, but cause a decreased and often greatly prolonged response. Clear structure-activity relations indicate that the receptor to which the drugs bind to produce the prolonged response can be the receptor for acetylcholine. Comparison of the effects of the drugs on the end plate potential and on the response to iontophoretically applied acetylcholine also shows that the effects of Xylocaine depend on the time course of receptor activation and are quite different from the effects of d-tubocurarine.
Permeability and Electrical Properties of Thin Lipid Membranes
Authors: Finkelstein Alan , Cass Albert
Published: May 2004

We present and discuss the permeability and electrical properties of thin lipid membranes, and the changes induced in these properties by several agents added to the aqueous phases after the membranes have formed. The unmodified membrane is virtually impermeable to ions and small "hydrophilic" solutes, but relatively permeable to water and "lipophilic" molecules. These properties are consistent with those predicted for a thin film of hydrocarbon through which matter is transported by dissolving in the membrane phase and then diffusing through it. The effect of cholesterol in reducing the water and "lipophilic" solute permeability is attributed to an increase of the "viscosity" of the hydrocarbon region, thus reducing the diffusion coefficient of molecules within this phase. The selective permeability of the membrane to iodide (I-) in the presence of iodine (I2) is attributed to the formation of polyiodides (perhaps I5-), which are presumed to be relatively soluble in the membrane because of their large size, and hence lower surface charge density. Thus, I2 acts as a carrier for I-. The effects of "excitability-inducing material" and the depsipeptides (particularly valinomycin) on ion permeability are reviewed. The effects of the polyene antibiotics (nystatin and amphotericin B) on ion permeability, discussed in greater detail, are the following: (a) membrane conductance increases with the 10th power of nystatin concentration; (b) the membrane is anion-selective but does not discriminate completely between anions and cations; (c) the membrane discriminates among anions on the basis of size; (d) membrane conductance decreases extraordinarily with increasing temperatures. Valinomycin and nystatin form independent conductance pathways in the same membrane, and, in the presence of both, the membrane can be reversibly shifted between a cation and anion permeable state by changes in temperature. It is suggested that nystatin produces pores in the membrane and valinomycin acts as a carrier.
A Kinetic Model for the Action of Xylocaine on Receptors for Acetylcholine
Authors: Steinbach A. B.
Published: May 2004

A kinetic scheme postulating the rapid formation of a partially active acetylcholine-receptor-drug complex from Xylocaine (or a derivative) and the active acetylcholine-receptor complex can account for the effects of Xylocaine and its derivatives at the neuromuscular junction. Transmembrane currents generated by an analogue computer programmed according to the scheme can exactly match end plate currents produced by nerve stimulation in the presence of the drugs. The scheme also accounts for the qualitatively different effects of the drugs on the end plate potential and on responses to iontophoretically applied acetylcholine. The analysis presented is consistent with very rapid reactions between acetylcholine and receptors, characterized by rate coefficients in the range 104 to 106 sec-1. It is based on the hypothesis that the activation of receptors by acetylcholine changes the structure of the receptors and thus their affinity for Xylocaine. The analysis does not require pharmacological separability of sodium and potassium conductances during the end plate current.
Analysis of Spike Electrogenesis of Eel Electroplaques with Phase Plane and Impedance Measurements
Authors: Morlock Noel L. , Benamy Daniel A. , Grundfest Harry
Published: May 2004

Eel electroplaques provide experimental conditions in which registration of phase plane trajectories (dV/dt vs. V) and impedance measurements with an AC Wheatstone bridge, in conjunction with spike electrogenesis describe quantitatively the ionic processes of the electrogenesis. Thus, these data employing as they do measurements of transients, permit an independent test of the validity of the assumptions which underlie the Hodgkin-Huxley equivalent circuit: independent ionic channels with fixed ionic batteries and exhibiting time-variant conductance changes with different kinetics for the different channels. The analysis accords with earlier findings on voltage-clamped electroplaques and this agreement confirms the validity of the equivalent circuit despite the fact that the current-voltage characteristics of the axons and electroplaques differ profoundly. As for squid axons, the equivalent circuit of the electroplaques has four branches: a capacity and three ionic channels. One of the latter is an invariant leak channel (GL) of high conductance. A K channel (GK) is fully open at rest, but rapidly undergoes inactivation when the cell is depolarized by more than 40 mv. GL and GK have a common inside negative emf (EK). A Na channel (GNa) with an inside positive emf (ENa) is closed at rest, but opens transiently upon depolarization.
Dynamics of Transcapillary Fluid Exchange
Authors: Wiederhielm Curt A.
Published: May 2004

Fluid balance at the capillary level has been simulated with an analogue computer program, based on experimental data on regional differences in capillary permeability, surface areas, and hydrostatic pressures. The program takes into account fluid and protein fluxes into and out of the interstitial space. Solutions are obtained for tissue hydrostatic pressure, tissue fluid osmotic pressure, interstitial space volume, and lymph flow. Simulation of a variety of physiological experiments and clinical disease states has yielded reasonable agreement between experimental data and data obtained by computer analysis. Dilution of the interstitial plasma protein pool with a consequent reduc6tion of its oncotic pressure appears to be a major factor, which prevents edema unless plasma oncotic pressures are reduced by 10–15 mm Hg or, alternatively, venous pressures are elevated by a similar amount. The computer analysis in all instances yields positive values for tissue pressure, in agreement with experimental data obtained by needle puncture. The negative tissue pressures observed in subcutaneous capsules can be reproduced in the computer program, if the interface between the capsule and the surrounding interstitial space is assumed to have the properties of a semipermeable membrane.