bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupling of Solute and Solvent Flows in Porous Lipid Bilayer Membranes
Authors: Andreoli Thomas E. , Schafer James A. , Troutman Susan L.
Published: May 2004

The present experiments were designed to evaluate coupling of water and nonelectrolyte flows in porous lipid bilayer membranes (i.e., in the presence of amphotericin B) in series with unstirred layers. Alterations in solute flux during osmosis, with respect to the flux in the absence of net water flow, could be related to two factors: first, changes in the diffusional component of solute flux referable to variations in solute concentrations at the membrane interfaces produced by osmotic flow through the unstirred layers; and second, coupling of solute and solvent flows within the membrane phase. Osmotic water flow in the same direction as solute flow increased substantially the net fluxes of glycerol and erythritol through the membranes, while osmotic flow in the opposite direction to glycerol flow reduced the net flux of that solute. The observed effects of osmotic water flow on the fluxes of these solutes were in reasonable agreement with predictions based on a model for coupling of solute and solvent flows within the membrane phase, and considerably in excess of the prediction for a diffusion process alone.
Hyperpolarization of a Barnacle Photoreceptor Membrane following Illumination
Authors: Koike H. , Brown H. Mack , Hagiwara S.
Published: May 2004

Membrane potential changes following illumination of a photoreceptor cell in the lateral ocellus of a barnacle (Balanus eburneus) were studied by means of intracellular recording and polarization techniques. Illumination produces a depolarizing response. When the illumination is terminated, the membrane potential temporarily becomes more negative than the resting potential prior to illumination. Although the amplitude of this postillumination hyperpolarization depends upon the intensity as well as the duration of the light pulse, the time course is fairly constant. The hyperpolarization is not associated with any significant membrane conductance increase and is abolished by 10-5 M ouabain. It diminishes when the external Na or K ions are removed. An intracellular injection of Na ions produces a hyperpolarization similar to that following illumination. It is suggested that the postillumination hyperpolarization is produced by an electrogenic Na pump which is activated by the Na influx during illumination.
Transient Phases of the Isometric Tetanus in Frog's Striated Muscle
Authors: Mittenthal Jay E. , Carlson Francis D.
Published: May 2004

In an isometric tetanus in frog's sartorius muscle tension approaches the plateau exponentially with rate constant α. α a depends on sarcomere length, s, and temperature, T, according to the Arrhenius equation

See PDF for Equation

for temperatures between 1 and 20°C and for sarcomere lengths 2.0–2.8 µm. The energy of activation, E, does not vary significantly with s; E = 13.9 ± 2.4 kcal/mole. A(s) decreases monotonically with s; A(2.1 µm) is about three times greater than A(2.8 µm). Late in relaxation active tension approaches zero exponentially with rate constant r. r decreases exponentially with increasing duration of tetanus, D, from r0 in a twitch to r∞ for large D. The rate constant for decrease of r with D increases with s and with T. r0 and r∞ obey the Arrhenius equation and decrease with increasing s.
Biphasic Potassium Contractures in Frog Muscle Fibers
Authors: Costantin L. L.
Published: May 2004

Potassium-induced contractures were studied in single fibers from the semitendinosus muscle of Rana pipiens. Contractures elicited by solutions containing 60–117 mM potassium and 120 mM chloride were biphasic, consisting of a rapid initial contraction with a duration at 23°C of less than 1 sec followed by a slow response with a duration of many seconds. At 13°C, the initial response was greatly prolonged so that the two responses virtually fused into a single smooth contracture. Membrane potential in high potassium, high chloride solutions underwent a transient peak depolarization, probably as a result of time-dependent changes in membrane conductance during depolarization. It is proposed that this complex time course of depolarization gives rise to the biphasic contracture response.
Rhodopsin and Porphyropsin Fields In the Adult Bullfrog Retina
Authors: Reuter Tom E. , White Richard H. , Wald George
Published: May 2004

Though it had been supposed earlier that the bullfrog undergoes a virtually complete metamorphosis of visual systems from vitamin A2 and porphyropsin in the tadpole to vitamin A1 and rhodopsin in the adult, the present observations show that the retina of the adult frog may contain as much as 30–40% porphyropsin, all of it segregated in the dorsal zone. The most dorsal quarter of the adult retina may contain 81–89% porphyropsin mixed with a minor amount of rhodopsin; the ventral half contains only rhodopsin. Further, the dorsal zone contains a two to three times higher concentration of visual pigments than the ventral retina. The pigment epithelium underlying the retina contains a corresponding distribution of vitamins A1 and A2, predominantly vitamin A2 in the dorsal pigment epithelium, exclusively vitamin A1 in the ventral zone. The retina accepts whatever vitamin A the pigment epithelium provides it with, and turns it into the corresponding visual pigment. Thus, a piece of light-adapted dorsal retina laid back on ventral pigment epithelium regenerates rhodopsin, whereas a piece of light-adapted ventral retina laid back on dorsal pigment epithelium regenerates predominantly porphyropsin. Vitamin A2 must be made from vitamin A1, by dehydrogenation at the 3,4-bond in the ring. This conversion must occur in the pigment epithelium, presumably through the action of a vitamin A-3,4-dehydrogenase. The essential change at metamorphosis is to make much less of this dehydrogenase, and to sequester it in the dorsal pigment epithelium. Some adult bullfrogs, perhaps characteristically taken in the summer, contain very little porphyropsin—only perhaps 5%—still sequestered in the dorsal retina. The gradient of light over the retinal surface has little if any effect on this distribution. The greater density of visual pigments in the dorsal retina, and perhaps also—although this is less clear—the presence of porphyropsin in this zone, has some ecological importance in increasing the retinal sensitivity to the dimmer and, on occasion, redder light received from below.
The Response of Duck Erythrocytes to Nonhemolytic Hypotonic Media
Authors: Kregenow Floyd M.
Published: May 2004

Duck erythrocytes were incubated in hypotonic media at tonicities which do not produce hemolysis. The cells' response can be divided into two phases: an initial rapid phase of osmotic swelling and a second more prolonged phase (volume regulatory phase) in which the cells shrink until they approach their initial isotonic volume. Shrinkage associated with the volume regulatory phase is the consequence of a nearly isosmotic loss of KCl and water from the cell. The potassium loss results from a transient increase in K efflux. There is also a small reduction in Na permeability. Changes in cell size during the volume regulatory phase are not altered by 10-4 M ouabain although this concentration of ouabain does change the cellular cation content. The over-all response of duck erythrocytes is considered as an example of "isosmotic intracellular regulation," a term used to describe a form of volume regulation common to euryhaline invertebrates which is achieved by adjusting the number of effective intracellular osmotic particles. The volume regulatory phase is discussed as the product of a membrane mechanism which is sensitive to some parameter associated with cell volume and is capable of regulating the loss of potassium from the cell. This mechanism is able to regulate cell size when the Na-K exchange, ouabain-inhibitable pump mechanism is blocked.
Two Light-Induced Processes in the Photoreceptor Cells of Limulus Ventral Eye
Authors: Lisman J. E. , Brown J. E.
Published: May 2004

The dark-adapted current-voltage (I-V) curve of a ventral photoreceptor cell of Limulus, measured by a voltage-clamp technique, has a high slope-resistance region more negative than resting voltage, a lower slope-resistance region between resting voltage and zero, and a negative slope-resistance region more positive than 0 v. With illumination, we find no unique voltage at which there is no light-induced current. At the termination of illumination, the I-V curve changes quickly, then recovers very slowly to a dark-adapted configuration. The voltage-clamp currents during and after illumination can be interpreted to arise from two separate processes. One process (fast) changes quickly with change in illumination, has a reversal potential at +20 mv, and has an I-V curve with positive slope resistance at all voltages. These properties are consistent with a light-induced change in membrane conductance to sodium ions. The other process (slow) changes slowly with changes in illumination, generates light-activated current at +20 mv, and has an I-V curve with a large region of negative slope resistance. The mechanism of this process cannot as yet be identified.
The Permeability of the Sodium Channel to Organic Cations in Myelinated Nerve
Authors: Hille Bertil
Published: May 2004

The relative permeability of sodium channels to 21 organic cations was studied in myelinated nerve fibers. Ionic currents under voltage-clamp conditions were measured in sodium-free solutions containing the test cation. The measured reversal potential and the Goldman equation were used to calculate relative permeabilities. The permeability sequence was: sodium ≈ hydroxylamine > hydrazine > ammonium ≈ formamidine ≈ guanidine ≈ hydroxyguanidine > aminoguanididine >> methylamine. The cations of the following compounds were not measurably permeant: N-methylhydroxylamine, methylhydrazine, methylamine, methylguanidine, acetamidine, dimethylamine, tetramethylammonium, tetraethylammonium, ethanolamine, choline, tris(hydroxymethyl)amino methane, imidazole, biguanide, and triaminoguanidine. Thus methyl and methylene groups render cations impermeant. The results can be explained on geometrical grounds by assuming that the sodium channel is an oxygen-lined pore about 3 A by 5 A in cross-section. One pair of oxygens is assumed to be an ionized carboxylic acid. Methyl and amino groups are wider than the 3 A width of the channel. Nevertheless, cations containing amino groups can slide through the channel by making hydrogen bonds to the oxygens. However, methyl groups, being unable to form hydrogen bonds, are too wide to pass through.
Dynamic Characteristics of Retinal Ganglion Cell Responses in Goldfish
Authors: Schellart Nico A. M. , Spekreijse Henk
Published: May 2004

A cross-correlation technique has been applied to quantify the dependence of the dynamic characteristics of retinal ganglion cell responses in goldfish on intensity, wavelength, spatial configuration, and spot size. Both theoretical and experimental evidence justify the use of the cross-correlation procedure which allows the completion of rather extensive measurements in a relatively short time. The findings indicate the following. (a) The shape of the amplitude characteristics depends on the energy per unit of time (power) falling within the center of a receptive field rather than on the intensity of the stimulus spot. For spot diameters of up to 1 mm, identical amplitude characteristics can be obtained by interchanging area and intensity. Therefore the receptor processes do not contribute to the change in the amplitude characteristics as a function of the power of the stimulus light. (b) For high frequencies the amplitude characteristics obtained as a function of power join together in a common envelope if plotted on an absolute sensitivity scale. For spontaneous ganglion cells this envelope holds over a range of three log units and the shape is identical for central and peripheral processes. (c) The amplitude characteristics of the central and peripheral processes converging to a ganglion cell are identical, irrespective of the sign (on or off) and the spectral coding of the response. Therefore we have no evidence for interneurons in the goldfish retina unique to the periphery of the receptive field.
Electrophysiological Properties of Cells in the Median Ocellus of Limulus
Authors: Nolte John , Brown Joel E.
Published: May 2004

Two types of photoreceptors are found in the median ocellus of Limulus. One type is maximally sensitive to ultraviolet (UV) light, the other to green light; they are called UV and VIS cells, respectively. Biphasic receptor potentials, consisting of a small initial hyperpolarizing phase and a later slow depolarizing phase, can be recorded from both receptor types. These biphasic responses are elicited in UV cells in response to long-wavelength light, and in VIS cells in response to ultraviolet light. Another type of hyperpolarizing response can be recorded in UV cells: after a bright ultraviolet stimulus, the cell remains depolarized; long-wavelength light rapidly returns the membrane potential to its value preceding ultraviolet illumination (this long-wavelength-induced potential change is called a "repolarizing response"). Also, a long-wavelength stimulus superimposed during a UV stimulus elicits a sustained repolarizing response. A third cell type (arhabdomeric cell) found in the median ocellus generates large action potentials and is maximally sensitive to UV light. Biphasic responses and repolarizing responses also can be recorded from arhabdomeric cells. The retina is divided into groups of cells; both UV cells and VIS cells can occur in the same group. UV cells in the same group are electrically coupled to one another and to an arhabdomeric cell.
The Inner Quaternary Ammonium Ion Receptor in Potassium Channels of the Node of Ranvier
Authors: Armstrong Clay M. , Hille Bertil
Published: May 2004

Quaternary ammonium ions were applied to the inside of single myelinated nerve fibers by diffusion from a cut end. The resulting block of potassium channels in the node of Ranvier was studied under voltage-clamp conditions. The results agree in almost all respects with similar studies by Armstrong of squid giant axons. With tetraethylammonium ion (TEA), pentyltriethylammonium ion (C5), or nonyltriethylammonium ion (C9) inside the node, potassium current during a depolarization begins to rise at the normal rate, reaches a peak, and then falls again. This unusual inactivation is more complete with C9 than with TEA. Larger depolarizations give more block. Thus the block of potassium channels grows with time and voltage during a depolarization. The block reverses with repolarization, but for C9 full reversal takes seconds at -75 mv. The reversal is faster in 120 mM KCl Ringer's and slower during a hyperpolarization to -125 mv. All of these effects contrast with the time and voltage-independent block of potassium, channels seen with external quaternary ammonium ions on the node of Ranvier. External TEA, C5, and C9 block without inactivation. The external quaternary ammonium ion receptor appears to be distinct from the inner one. Apparently the inner quaternary ammonium ion receptor can be reached only when the activation gate for potassium channels is open. We suggest that the inner receptor lies within the channel and that the channel is a pore with its activation gate near the axoplasmic end.
Mechanical Properties of the Sarcolemma and Myoplasm in Frog Muscle as a Function of Sarcomere Length
Authors: Rapoport Stanley I.
Published: May 2004

The elastimeter method was applied to the single muscle fiber of the frog semitendinosus to obtain the elastic moduli of the sarcolemma and myoplasm, as well as their relative contributions to resting fiber tension at different extensions. A bleb which was sucked into a flat-mouthed pipette at the fiber surface separated into an external sarcolemmal membrane and a thick inner myoplasmic region. Measurements showed that the sarcolemma does not contribute to intact fiber tension at sarcomere lengths below 3 µ. It was estimated that the sarcolemma contributed on the order of 10% to intact fiber tension at sarcomere lengths between 3 and 3.75 µ, and more so with further extension. Between these sarcomere lengths, the sarcolemma can be linearly extended and has a longitudinal elastic modulus of 5 x 106 dyne/cm2 (assuming a thickness of 0.1 µ). Resistance to deformation of the inner bleb region is due to myoplasmic elasticity. The myoplasmic elastic modulus was estimated by use of a model and was used to predict a fiber length-tension curve which agreed approximately with observations.
Correlated Electrophysiological and Ultrastructural Studies of a Crustacean Motor Unit
Authors: Sherman R. G. , Atwood H. L.
Published: May 2004

Structural and functional interrelationships between the pre- and postsynaptic elements of a singly motor innervated crab muscle (stretcher of Hyas araneus L.) were examined using electrophysiological and electron microscopic techniques. Excitatory postsynaptic potential (EPSP) amplitude at 1 Hz was found to be inversely related to the extent of facilitation, and directly related both to the amount of transmitter released at 1 Hz and the muscle fiber input resistance (Rin). The extent of facilitation (Fe), taken as the ratio of the EPSP amplitude at 10 Hz to that 1 Hz, was inversely related to muscle fiber Rin, τm, and sarcomere length. Sarcomere length was directly related to Rin and τm. The excitatory nerve terminals of low Fe muscle fibers had larger neuromuscular synapses than did those of high Fe fibers. Inhibitory axo-axonal synapses were more often found in low Fe muscle fibers. These structural features may account for the greater release of transmitter at low frequencies from the low Fe nerve terminals as well as provide for a greater amount of presynaptic inhibition of low Fe muscle fibers. The implications of these findings for the development and physiological performance of the crustacean motor unit are discussed. It is proposed that both nerve and muscle fiber properties may be determined by the developmental pattern of nerve growth.
On the Inhibition of Muscle Contraction Caused by Exposure to Hypertonic Solutions
Authors: Miyamoto M. , Hubbard J. I.
Published: May 2004

The evidence supporting a site of inhibition of excitation contraction (E-C) coupling near the plasma membrane (the "glycerol effect," the K+-potentiating effect) for muscle in hypertonic solution was reinvestigated. It was found, using whole frog sartorii, that there was a rehydration of muscle soaked in glycerol Ringer after 30 min and a large swelling (to 140% after 1 hr soaking) upon return of the muscle to normal Ringer, suggesting that significant amounts of glycerol enter the fibers during this time. While contrary to the original report of the glycerol effect, this finding was consistent with other studies involving the use of single fibers. Also reexamined was the potentiating effect of K+ on the hypertonic inhibition of muscle contraction. It was found that muscles exposed to this KCl pretreatment swell so that they are less dehydrated in hypertonic solutions, thus accounting for the observed potentiation. After being treated instead with a K2-tartrate Ringer solution, muscles did not swell and, as determined with twitch recordings, did not display any potentiation in hypertonic solutions—even though the [K+] was higher than an osmotically equivalent KCl solution. The evidence was thus consistent with alternative hypotheses in which inhibition of contraction occurs at a later stage in E-C coupling or involves the contractile process itself.
Dark Ionic Flux and the Effects of Light in Isolated Rod Outer Segments
Authors: Korenbrot Juan I. , Cone Richard A.
Published: May 2004

We have determined the permeability properties of freshly isolated frog rod outer segments by observing their osmotic behavior in a simple continuous flow apparatus. Outer segments obtained by gently shaking a retina are sensitive but nonideal osmometers; a small restoring force prevents them from shrinking or swelling quite as much as expected for ideal behavior. We find that Na+, Cl-, No3-, glycerol, acetate, and ammonium rapidly enter the outer segment, but K+, SO4=, and melezitose appear impermeable. The Na flux is rectified; for concentration gradients in the physiological range, 2 x 109 Na+ ions/sec enter the outer segment, but we detect no efflux of Na+, under our conditions, when the gradient is reversed. Illumination of the outer segment produces a specific increase in the resistance to Na+ influx, but has no effect on the flux of other solutes. This light-dependent Na+ resistance increases linearly with the number of rhodopsin molecules bleached. We find that excitation of a single rhodopsin molecule produces a transient (∼1 sec) "photoresistance" which reduces the Na+ influx by about 1%, thus preventing the entry of about 107 Na+ ions. At considerably higher light levels, a stable afterimage resistance appears which reduces the Na influx by one-half when 106 rhodopsin molecules are bleached per rod. We have incorporated these findings into a model for the electrophysiological characteristics of the receptor.
An Active Electrical Response in Fibroblasts
Authors: Nelson Phillip G. , Peacock John , Minna John
Published: May 2004

L cells have a resting potential of about -16 mv (internal negative) at 37°C in Dulbecco's modified Eagle's medium containing 10% fetal calf serum and a potassium concentration of 5.4 mM. Membrane resistivity is about 20,000 Ωcm2 when the surface filopodia described by others are taken into account. Mechanical and electrical stimuli can evoke an active response from mouse L cells, cells of the 3T3 line, and normal fibroblasts which we have termed hyperpolarizing activation or the H.A. response. This consists of a prolonged (3–5 sec) increase in the membrane permeability by a factor of 2–10 with a parallel increase in membrane potential to about -50 mv. The reversal potential for the H.A. response is -80 mv. The resting cells are depolarized to about -12 mv when the external medium contains 27 mM potassium, and the potential reached at the peak of the H.A. response is about -30 mv. The reversal potential for the H.A. response is about -40 mv in 27 mM external potassium. This effect of potassium ions on the reversal potential of the H.A. response leads us to conclude that the response represents an increase in membrane permeability, predominantly to potassium, by at least a factor of five. This increase must be greater than 20-fold if previous measurements of the ratio of potassium permeability to chloride permeability in L cells are valid for the preparation used in the present study.
Photodynamic Alteration of Sodium Currents in Lobster Axons
Authors: Pooler John
Published: May 2004

Photodynamic alteration of lobster giant axons drastically changed the magnitude and kinetics of sodium currents seen under voltage clamp using the sucrose gap technique. Illumination of axons following treatment with acridine orange or eosin Y decreased the maximum sodium conductance to a zero asymptote as an exponential function of illumination time. Normal sodium inactivation was slowed, with τh more than doubled depending on experimental conditions. A second slower inactivation rate developed occasionally. τh was altered little, if at all. Sodium current "tails" were not prolonged. At maximum light intensity and with eosin Y as sensitizer leakage current increased after 4–10 sec in light. These changes were irreversible. Decreases in maximum sodium conductance correlated highly with increases in time to peak sodium current. The magnitude of change varied linearly with light intensity. The action spectra for eosin Y and acridine orange peaked near 545 and 505 nm, respectively. The magnitude of change varied with preillumination dye exposure time in a quasi-exponential approach to a maximum effect. Sodium dithionite protected the axon from photodynamic change.
Active Transport of Potassium by the Giant Neuron of the Aplysia Abdominal Ganglion
Authors: Russell J. M. , Brown A. M.
Published: May 2004

We measured the internal potassium activity, aiK, and membrane potential, Em, simultaneously in 111 R2 giant neurons of Aplysia californica. aiK was 165.3 ± 3.4 mM, Em was -47.8 ± 0.9 mv, and EK calculated using the Nernst equation was -76.9 ± 0.05 mv. Such values were maintained for as long as 6 hr of continuous recording in untreated cells, aiK fell exponentially after the following treatments: cooling to 0.5°–4°C, ouabain, zero external potassium, 2,4-dinitrophenol, and cyanide. The effects of cooling and zero potassium were reversible. Potassium permeability was calculated from net potassium flux using the constant field equation and ranged from 2.6 to 18.5 x 10-8 cm/sec. We conclude that potassium is actively transported into this neuron against a 30–40 mv electrochemical gradient.
The Effect of Glycerol Treatment of Voltage-Clamped Snake Muscle Fibers
Authors: Washio Hiroshi
Published: May 2004

The effect of glycerol treatment on the membrane currents and tension development was studied in voltage clamped snake muscle fibers. In muscle fibers which were exposed for 1 h to a normal saline containing 400 mM glycerol and then returned to a normal medium, graded depolarizations did not accompany contractile responses. However, when the fiber was depolarized to a certain level, an increment of outward current appeared which partially inactivated with time. The threshold for delayed rectification in glycerol-treated fibers was almost the same as that of intact fibers in spite of the absence of contractile tension. The results suggest that the delayed rectification may be attributed at least in part to the surface membrane and that the contractile activation probably does not depend simply on the inactivating outward currents through the delayed rectification channel.
Adaptation in the Ventral Eye of Limulus is Functionally Independent of the Photochemical Cycle, Membrane Potential, and Membrane Resistance
Authors: Fein A. , DeVoe R. D.
Published: May 2004

The early receptor potential (ERP), membrane potential, membrane resistance, and sensitivity were measured during light and/or dark adaptation in the ventral eye of Limulus. After a bright flash, the ERP amplitude recovered with a time constant of 100 ms, whereas the sensitivity recovered with an initial time constant of 20 s. When a strong adapting light was turned off, the recovery of membrane potential and of membrane resistance had time-courses similar to each other, and both recovered more rapidly than the sensitivity. The receptor depolarization was compared during dark adaptation after strong illumination and during light adaptation with weaker illumination; at equal sensitivities the cell was more depolarized during light adaptation than during dark adaptation. Finally, the waveforms of responses to flashes were compared during dark adaptation after strong illumination and during light adaptation with weaker illumination. At equal sensitivities (equal amplitude responses for identical flashes), the responses during light adaptation had faster time-courses than the responses during dark adaptation. Thus neither the photochemical cycle nor the membrane potential nor the membrane resistance is related to sensitivity changes during dark adaptation in the photoreceptors of the ventral eye. By elimination, these results imply that there are (unknown) intermediate process(es) responsible for adaptation interposed between the photochemical cycle and the electrical properties of the photoreceptor.
Disc Electrophoresis of Extracts from the Taste Buds Located in Circumvallate Papillae of Rat Tongues
Authors: Uehara Seiji
Published: May 2004

The epithelium of the circumvallate papillae of rat tongues was stripped off by treatment with 0.005% elastase in a state when many taste buds were present. The taste buds were isolated from the stripped epithelium by further treatment with 0.005% elastase and 0.08% trypsin. A protein which was thought to be characteristic of taste buds was found from semimicro disc polyacrylamide gel electrophoretic studies of the stripped epithelia with and without taste buds. This result was supported by micro disc polyacrylamide gel electrophoretic studies of isolated taste buds.
Quantal Mechanism of Transmitter Release during Progressive Depletion of the Presynaptic Stores at a Ganglionic Synapse
Authors: Sacchi Oscar , Perri Virgilio
Published: May 2004

In the present experiments we interfered with the mechanism of acetylcholine (ACh) synthesis in the rat superior cervical ganglion by impairing the supply of either the choline group (hemicholinium no. 3 [HC-3]treatment) or the acetyl group (thiamine deprivation). Under both conditions stimulation causes in the ganglion a progressive decline in ACh output associated with a depletion of transmitter tissue content. ACh release from the terminals of a single preganglionic fiber was estimated from the quantum content value of the evoked excitatory postsynaptic potentials (EPSP's) recorded intracellularly in the ganglion neuron under test. The present observations indicate that Poisson statistics describe transmitter release at either low or high release levels. Furthermore, the progressive decline in the rate of ACh output occurring during repetitive stimulation is shown to correspond to a progressive decrease in the number of transmitter quanta released per impulse and not to any modification in the size of individual quanta. Some 8,000 transmitter quanta proved to represent the presynaptic transmitter store initially present in those terminals on a neuron that are activated by stimulation of a single preganglionic fiber. Speculations are considered about synaptic efficacy and nerve connections in rat autonomic ganglia. It is suggested that six preganglionic fibers represent the mean input to a ganglion neuron.
Rapid Changes of Potassium Concentration at the Outer Surface of Exposed Single Neurons during Membrane Current Flow
Authors: Neher E. , Lux H. D.
Published: May 2004

K+-sensitive liquid ion-exchanger microelectrodes are shown to be capable of measuring concentration changes which occur on a millisecond time scale. However, some quaternary ammonium ions, such as tetraethylammonium and acetylcholine, are able to block electrode function when present in concentrations as low as 10-4 to 10-3 M. Changes in extracellular potassium concentration caused by spike activity or voltage clamp pulses of exposed single neurons of the snail Helix pomatia may be measured by these electrodes. Quantitative analysis shows that the total amount of excess potassium found in the vicinity of the cell a short time after a clamp pulse, is in relatively good agreement with the amount of potassium carried by the membrane current.
Action Spectra and Adaptation Properties of Carp Photoreceptors
Authors: Witkovsky P. , Nelson J. , Ripps H.
Published: May 2004

The mass photoreceptor response of the isolated carp retina was studied after immersing the tissue in aspartate-Ringer solution. Two electro-retinogram components were isolated by differential depth recording: a fast cornea-negative wave, arising in the receptor layer, and a slow, cornea-negative wave arising at some level proximal to the photoreceptors. Only the fast component was investigated further. In complete dark adaptation, its action spectrum peaked near 540 nm and indicated input from both porphyropsin-containing rods (λmax ≈ 525 nm) and cones with longer wavelength sensitivity. Under photopic conditions a broad action spectrum, λmax ≈ 580 nm was seen. In the presence of chromatic backgrounds, the photopic curve could be fractionated into three components whose action spectra agreed reasonably well with the spectral characteristics of blue, green, and red cone pigments of the goldfish. In parallel studies, the carp rod pigment was studied in situ by transmission densitometry. The reduction in optical density after a full bleach averaged 0.28 at its λmax 525 nm. In the isolated retina no regeneration of rod pigment occurred within 2 h after bleaching. The bleaching power of background fields used in adaptation experiments was determined directly. Both rods and cones generated increment threshold functions with slopes of +1 on log-log coordinates over a 3–4 log range of background intensities. Background fields which bleached less than 0.5% rod pigment nevertheless diminished photoreceptor sensitivity. The degree and rate of recovery of receptor sensitivity after exposure to a background field was a function of the total flux (I x t) of the field. Rod saturation, i.e. the abolition of rod voltages, occurred after ≈12% of rod pigment was bleached. In light-adapted retinas bathed in normal Ringer solution, a small test flash elicited a larger response in the presence of an annular background field than when it fell upon a dark retina. The enhancement was not observed in aspartate-treated retinas.
Neural Organization of a Molluscan Visual System
Authors: Alkon Daniel L.
Published: May 2004

Intracellular recording was used to study the response to light of second order visual cells within the optic ganglion of Hermissenda crassicornis. Simultaneous recordings revealed that type B but not type A photoreceptors inhibit the second order cells. Additional details of the neural organization of the visual system were obtained. Possible functional implications of this neural organization are discussed.
Hair Cell Generator Potentials
Authors: Alkon Daniel L. , Bak Anthony
Published: May 2004

A technique is introduced using a piezoelectric device to stimulate hair cells of a molluscan statocyst while recording their responses intracellularly. Statocyst displacements produced with the technique are calibrated with stroboscopic photography. Properties of the hair cells' response to currents and mechanical stimulation are studied. The hair cell generator potential arises from a conductance increase and, for a certain range, is a logarithmic function of the amplitude of the displacement stimulus.
Influence of the Ionic Composition of Fluid Medium on Red Cell Aggregation
Authors: Jan Kung-Ming , Chien Shu
Published: May 2004

The effects of ionic strength and cationic valency of the fluid medium on the surface potential and dextran-induced aggregation of red blood cells (RBC's) were investigated. The zeta potential was calculated from cell mobility in a microelectrophoresis apparatus; the degree of aggregation of normal and neuraminidase-treated RBC's in dextrans (Dx 40 and Dx 80) was quantified by microscopic observation, measurement of erythrocyte sedimentation rate, and determination of low-shear viscosity. A decrease in ionic strength caused a reduction in aggregation of normal RBC's in dextrans, but had no effect on the aggregation of neuraminidase-treated RBC's. These findings reflect an increase in electrostatic repulsive force between normal RBC's by the reduction in ionic strength due to (a) a decrease in the screening of surface charge by counter-ions and (b) an increase in the thickness of the electric double layer. Divalent cations (Ca++, Mg++, and Ba++) increased aggregation of normal RBC's in dextrans, but had no effect on the aggregation of neuraminidase-treated RBC's. These effects of the divalent cations are attributable to a decrease in surface potential of normal RBC's and a shrinkage of the electric double layer. It is concluded that the surface charge of RBC's plays a significant role in cell-to-cell interactions.
Chloride Transport in Porous Lipid Bilayer Membranes
Authors: Andreoli Thomas E. , Watkins Mary L.
Published: May 2004

This paper describes dissipative Cl- transport in "porous" lipid bilayer membranes, i.e., cholesterol-containing membranes exposed to 1–3 x 10-7 M amphotericin B. PDCl (cm·s-1), the diffusional permeability coefficient for Cl-, estimated from unidirectional 36Cl- fluxes at zero volume flow, varied linearly with the membrane conductance (Gm, Ω-1·cm-2) when the contributions of unstirred layers to the resistance to tracer diffusion were relatively small with respect to the membranes; in 0.05 M NaCl, PDCl was 1.36 x 10-4 cm·s-1 when Gm was 0.02 Ω-1·cm-2. Net chloride fluxes were measured either in the presence of imposed concentration gradients or electrical potential differences. Under both sets of conditions: the values of PDCl computed from zero volume flow experiments described net chloride fluxes; the net chloride fluxes accounted for ∼90–95% of the membrane current density; and, the chloride flux ratio conformed to the Ussing independence relationship. Thus, it is likely that Cl- traversed aqueous pores in these anion-permselective membranes via a simple diffusion process. The zero current membrane potentials measured when the aqueous phases contained asymmetrical NaCl solutions could be expressed in terms of the Goldman-Hodgkin-Katz constant field equation, assuming that the PDNa/PDCl ratio was 0.05. In symmetrical salt solutions, the current-voltage properties of these membranes were linear; in asymmetrical NaCl solutions, the membranes exhibited electrical rectification consistent with constant-field theory. It seems likely that the space charge density in these porous membranes is sufficiently low that the potential gradient within the membranes is approximately linear; and, that the pores are not electrically neutral, presumably because the Debye length within the membrane phase approximates the membrane thickness.
Response of the Frog Skin to Steady-State Voltage Clamping
Authors: Mandel Lazaro J. , Curran Peter F.
Published: May 2004

Active Na transport across frog skin was separated from passive Na movement utilizing urea influx as a measure of passive (shunt) permeability. In this manner, the response of the overall active Na transport system to an applied potential was determined over a range from +200 mV to -100 mV. Active Na transport displays saturation as a function of applied potential, and both the level of saturation and the potential at which it is achieved are functions of the Na concentration in the external solution. The saturation with potential appears to involve a different step in the transport process than the saturation of Na flux as a function of external Na concentration. The observations can be qualitatively described by either a one-barrier or two-barrier model of the Na transport system.
The Inhibition of Sodium Currents in Myelinated Nerve by Quaternary Derivatives of Lidocaine
Authors: Strichartz Gary R.
Published: May 2004

The inhibition of sodium currents by quaternary derivatives of lidocaine was studied in single myelinated nerve fibers. Membrane currents were diminished little by external quaternary lidocaine (QX). QX present in the axoplasm (<0.5 mM) inhibited sodium currents by more than 90%. Inhibition occurred as the sum of a constant, tonic phase and a variable, voltage-sensitive phase. The voltage-sensitive inhibition was favored by the application of membrane potential patterns which produce large depolarizations when sodium channels are open. Voltage-sensitive inhibition could be reversed by small depolarizations which opened sodium channels. One explanation of this observation is that QX molecules enter open sodium channels from the axoplasmic side and bind within the channels. The voltage dependence of the inhibition by QX suggests that the drug binds at a site which is about halfway down the electrical gradient from inside to outside of the sodium channel.
Phototropism and Local Adaptation in Phycomyces Sporangiophores
Authors: Dennison David S. , Bozof Richard P.
Published: May 2004

Phototropic responses to unilateral ultraviolet stimuli were studied to determine whether the response of one side of the cell is affected by the previous exposure of the opposite side to ultraviolet. It has been found that the direction of bending is not parallel to the stimulus direction, but is along a straight line rotated 17° clockwise from the stimulus direction. This deviation indicates that the photoreceptors may be in a state of continual clockwise rotation. If before the stimulus the cell is exposed briefly to ultraviolet and rotated through 90°, the response is not along the 17° line, but is deviated a greater or lesser amount, depending on whether the 90° rotation is clockwise or counterclockwise. This difference is evidence that the first ultraviolet exposure leaves a persistent patch of light-adapted receptors and the shaded part of the cell remains dark adapted. The phototropic stimulus straddles the edge between light- and dark-adapted regions, and the differing responses of the two regions affects the direction of phototropic bending. A phototropic mechanism is proposed which combines the features of local adaptation and photoreceptor rotation.
The Range of Attractant Concentrations for Bacterial Chemotaxis and the Threshold and Size of Response over This Range
Authors: Mesibov Robert , Ordal George W. , Adler Julius
Published: May 2004

Attractant was added to a suspension of bacteria (the background concentration of attractant) and then these bacteria were exposed to a yet higher concentration of attractant in a capillary. Chemotaxis was measured by determining how many bacteria accumulated in the capillary. The response range for chemotaxis lies between the threshold concentration and the saturating concentration. The breadth of this range is different for attractants detected by different chemoreceptors. Attractants detected by the same chemoreceptor can have their response ranges in widely different places. Over the center of the response range (on a logarithmic scale), bacteria give similar sized responses to similar fractional increases of concentration, i.e. they respond to ratios of attractant concentration, but the response peaks at the center of the range. The size of the response is different for attractants detected by different chemoreceptors. For a detectable response, a smaller increase in attractant concentration is needed for attractants detected by some chemoreceptors than for attractants detected by others. Although the data are inadequate, it appears that the Weber law may be observed over a wide range of concentrations for some attractants but not for others. In the Appendix we aim to explain some of these results in terms of the interaction of an attractant with its chemoreceptor according to the law of mass action.
Energetics of Contraction in Phasic and Tonic Skeletal Muscles of the Chicken
Authors: Rall Jack A. , Schottelius B. A.
Published: May 2004

Comparative energetics of chicken latissimus dorsi muscles, tonic anterior (ALD) and phasic posterior (PLD), were investigated by measuring initial heat production. Heat components were analyzed in terms of the equation:

E = A + W + αF(Δ¯L) + f(P, t)

As the muscles were stretched by increments, heat produced in isometric twitches and tetani decreased in a linear fashion. Two processes are involved: one tension independent, the activation heat, or A; and the other tension dependent, Wi + αF(Δ¯L) + f(P, t). In twitches, A, per unit tension, is equivalent in the PLD and ALD. Tension-dependent heat, per unit tension, is greater in the PLD due to Wi; but tension-time-related heat, f(P, t), per unit tension, is similar in both muscles. In tetanic contractions, differences in A and f(P, t), per unit tension, are attributed to the greater Vmax in the PLD. The differences in the energetics of isometric contractions in the PLD and ALD, therefore, can be explained by inherent differences in tension development, compliance, and myosin and reticular ATPase activities. Data from isotonic twitches were quantified by means of the equivalent tension technique. Both muscles exhibited an extra heat associated with shortening, αF(Δ¯L). In the PLD, the ratio αF/Pot is greater; it is load independent and ½ the value of a/Po in both muscles. Enthalpy efficiency, We + Wi/E, is comparable in both muscles. A Fenn effect is observed only when isotonic energy liberation is compared to a decreasing isometric energy expenditure base line.
Thermal Sensitivity of Lateral Inhibition in Limulus Eye
Authors: Adolph Alan R.
Published: May 2004

The effectiveness of lateral inhibition, measured as spike response decrement in a test ommatidium, produced by activity in a group of neighboring ommatidia, decreases as temperature decreases (Q10 of 2.6). The corresponding sensory transducer-spike encoding processes have a weaker temperature dependence (Q10 of 1.6). Relative synaptic delay, the time difference between the latency of inhibition onset and the latency of test receptor excitation, has a strong temperature dependence (Q10 of 5), while receptor potential onset latency (Q10 of 1.4) and optic nerve spike conduction velocity (Q10 of 1.7), two factors inherent in relative synaptic delay, are less temperature sensitive. Oscillations of optic nerve spike response ("bursting") may be produced by thermal adjustment of temperature-sensitive parameters of the lateral inhibitory network in the retina. Burst interval has a strong temperature dependence (Q10 of 2.4) and broad interspike interval distribution compared to the thermal sensitivity (Q10 of 1.4) and narrow spike interval spectrum of the response of a single unit within the bursting group.
A Micropuncture Investigation of the Whole Tissue Mechanism of Electrolyte Secretion by the In Vitro Rabbit Pancreas
Authors: Swanson C. H. , Solomon A. K.
Published: May 2004

Micropuncture techniques have been used to examine electrolyte secretion by the in vitro rabbit pancreas. The concentration profiles of the major secreted ions and digestive protein and the electrical potential profile within the pancreatic ductal system have been determined during spontaneous and secretin-stimulated secretion. The active transport of both Na and HCO3 are the rate-controlling steps in primary secretion. Spontaneous secretion is produced primarily within the intralobular ducts. The anion composition of this primary secretion depends on the secretion rate with HCO3 ranging from about 70 meq/liter at low rates to about 110 meq/liter at high rates. With secretin stimulation the smaller extralobular ducts also secrete and this extralobular secretion has a higher HCO2 content than that of the intralobular secretion. In the main collecting duct the anion composition of the juice is modified further by Cl-HCO3 exchange which appears to be a passive process depending on the average residence time of the juice in the main duct.
Measurement of the Permeability of Biological Membranes Application to the glomerular wall
Authors: Verniory A. , Du Bois R. , Decoodt P. , Gassee J. P. , Lambert P. P.
Published: May 2004

The transport equation describing the flow of solute across a membrane has been modified on the basis of theoretical studies calculating the drag of a sphere moving in a viscous liquid undergoing Poiseuille flow inside a cylinder. It is shown that different frictional resistance terms should be introduced to calculate the contributions of diffusion and convection. New sieving equations are derived to calculate r and Ap/Δx (respectively, the pore radius and the total area of the pores per unit of path length). These equations provide a better agreement than the older formulas between the calculated and the experimental glomerular sieving coefficients for [125I]polyvinylpyrrolidone (PVP) fractions with a mean equivalent radius between 19 and 37 Å. From r and Ap/Δx, the mean effective glomerular filtration pressure has been calculated, applying Poiseuille's law. A value of 15.4 mm Hg has been derived from the mean sieving curve obtained from 23 experiments performed on normal anesthetized dogs.