bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonviral Interferon Inducers
Authors: Merigan Thomas C. , De Clercq Erik , Bausek Gerald H.
Published: May 2004

Interferon production can be stimulated by a great variety of microbial and nonmicrobial agents other than viruses. The nonmicrobial inducers can be divided into polyanions, mitogens, and a miscellaneous category including the various endotoxins and antibiotics. The polyanions appear to require a stable, high molecular weight backbone and a high density of free anionic groups whether they are polynucleotides, plastics, or polysaccharides. Mitogen-induced interferon appears to be but one of a constellation of substances produced following lymphocyte transformation. The process of transformation can be stimulated either by specific immune recognition or non-specifically by phytohemagglutinin. Synthetic polynucleotide inducers are active; the thermostable, double-stranded RNA's are much more active than the double-stranded DNA's or 1-, 3-, or 4-stranded RNA's. Some success has been obtained with potentiation of nucleotide inducers through the use of polycationic substances, complexing with a polysaccharide, concurrent administration of a metabolic antagonist, or substitution of phosphate by thiophosphate in the polynucleotide backbone. The stages in the interaction of interferon stimulating RNA and cells can be divided into three steps: first, binding to cell surface, next, a temperature dependent "recognition" step, and finally, degradation and utilization of monomers in cellular RNA synthesis; the critical recognition site has not yet been determined. The vast majority of cell-associated polynucleotide remains at the surface of the cell. Information from animal models resembling human diseases suggests that certain of these nucleotide inducers may have clinical usefulness in therapy or prophylaxis.
Response Properties of a Sensory Hair Excised from Venus's Flytrap
Authors: Benolken R. M. , Jacobson S. L.
Published: May 2004

Multicellular sensory hairs were excised from the leaf of Venus's flytrap, and the sensory cells were identified by a destructive dissection technique. The sensory layer includes a radially symmetrical rosette of 20–30 apparently identical cells, and the sensory cells are organized in a plane normal to the long axis of the sensory hair. The sensory cells were probed with intracellular glass electrodes. The resting membrane potential was about -80 mv, and the response to a mechanical stimulus consisted of a graded response and an "action potential." The action potential appears to be similar to the action potential which propagates over the surface of the leaf. In the absence of stimulation, the upper and lower membranes of a single sensory cell behave in an electrically symmetrical fashion. Upon stimulation, however, the upper and lower membranes become electrically asymmetrical. Limiting values for the response asymmetry were calculated on the hypothesis of an electrical model consistent with the histology of the sensory cells.
Cellular Mechanisms of Interferon Production
Authors: Vilček Jan
Published: May 2004

Rabbit kidney cell cultures stimulated with either double-stranded polyinosinate-polycytidylate (poly I:poly C) or with ultraviolet-irradiated Newcastle disease virus (UV-NDV) produce two types of interferon response, designated "early" and "late," respectively. The early response is suppressed by inhibitors of RNA or protein synthesis and is therefore thought to represent de novo synthesis of interferon. Circumstantial evidence suggested that this interferon response is regulated by a translation control mechanism. Late interferon production with poly I:poly C only took place in the presence of inhibitors of RNA or protein synthesis. The late interferon is therefore likely to be derived by the activation of an interferon precursor. The stimulation of late poly I:poly C-induced interferon production by cycloheximide suggested the existence of a second, posttranslational level of control of interferon production. This posttranslation control seems to be activated by interferon. UV-NDV can probably suppress the synthesis of the posttranslation inhibitory protein, and therefore it stimulates a late interferon response in the absence of inhibitors of RNA or protein synthesis. It is postulated that both the translation and posttranslation inhibitor participate in the development of a cellular refractory state to repeated interferon stimulation. The picture of interferon which emerges from this study is one of a heterogenous class of proteins whose production is controlled by cellular repressors acting at various levels.
Sarcoplasmic Reticulum
Authors: Duggan P. F. , Martonosi A.
Published: May 2004

Fragmented sarcoplasmic reticulum (FSR) membranes isolated from rabbit skeletal muscle are impermeable to inulin-14C (mol wt 5,000), and dextran-14C (mol wt 15,000–90,000) at pH 7.0–9.0, yielding an excluded space of 4–5 µl/mg microsomal protein. In the same pH range urea and sucrose readily penetrate the FSR membrane. EDTA or EGTA (1 mM) increased the permeability of microsomes to inulin-14C or dextran-14C at pH 8–9, parallel with the lowering of the FSR-bound Ca++ content from initial levels of 20 nmoles/mg protein to 1–3 nmoles/mg protein. EGTA was as effective as EDTA, although causing little change in the Mg++ content of FSR. The permeability increase caused by chelating agents results from the combined effects of high pH and cation depletion. As inulin began to penetrate the membrane there was an abrupt fall in the rate of Ca++ uptake and a simultaneous rise in ATPase activity. At 40°C inulin penetration occurred at pH 7.0 with 1 mM EDTA and at pH 9.0 without EDTA, suggesting increased permeability of FSR membranes. This accords with the higher rate of Ca++ release from FSR at temperatures over 30°C. The penetration of microsomal membranes by anions is markedly influenced by charge effects. At low ionic strength and alkaline pH acetate and Cl are partially excluded from microsomes when applied in concentrations not exceeding 1 mM, presumably due to the Donnan effect. Penetration of microsomal water space by acetate and Cl occurs at ionic strengths sufficiently high to minimize charge repulsions.
Sodium Movements in the Human Red Blood Cell
Authors: Sachs John R.
Published: May 2004

Measurements were made of the sodium outflux rate constant, okNa, and sodium influx rate constant, ikNa, at varying concentrations of extracellular (Nao) and intracellular (Nac) sodium. okNa increases with increasing [Nao] in the presence of extracellular potassium (Ko) and in solutions containing ouabain. In K-free solutions which do not contain ouabain, okNa falls as [Nao] rises from 0 to 6 mM; above 6 mM, okNa increases with increasing [Nao]. Part of the Na outflux which occurs in solutions free of Na and K disappears when the cells are starved or when the measurements are made in solutions containing ouabain. As [Nao] increases from 0 to 6 mM, ikNa decreases, suggesting that sites involved in the sodium influx are becoming saturated. As [Nac] increases, okNa at first increases and then decreases; this relation between okNa and [Nac] is found when the measurements are made in high Na, high K solutions; high Na, K-free solutions; and in (Na + K)-free solutions. The relation may be the consequence of the requirement that more than one Na ion must react with the transport mechanism at the inner surface of the membrane before transport occurs. Further evidence has been obtained that the ouabain-inhibited Na outflux and Na influx in K-free solutions represent an exchange of Nac for Nao via the Na-K pump mechanism.
Characteristics of Electrogenic Sodium Pumping in Rat Myometrium
Authors: Taylor Grahame S. , Paton David M. , Daniel E. E.
Published: May 2004

Sodium-rich myometrium, obtained from the uteri of pregnant rats, rapidly hyperpolarized when 4.6–120 mM potassium was added to the bathing medium at 37°C. Hyperpolarization was due to sodium pumping since the process was markedly temperature dependent, was abolished by ouabain, and required both intracellular sodium and extracellular potassium. The observed membrane potential exceeded the calculated potassium equilibrium potential during hyperpolarization providing evidence that sodium pumping was electrogenic. Hyperpolarization was reduced in the presence of chloride. The rate of sodium pumping may influence potassium permeability since potassium apparently did not short-circuit the pump during hyperpolarization.
Membrane Conductances and Spectral Sensitivities of Pecten Photoreceptors
Authors: McReynolds John S. , Gorman A. L. F.
Published: May 2004

The electrical and spectral properties of depolarizing (proximal) and hyperpolarizing (distal) photoreceptors in the eye of the scallop, Pecten irradians, were examined. Both depolarizing and hyperpolarizing responses are associated with an increase in membrane conductance; in addition, the depolarizing response is characterized by a secondary decrease in conductance at light intensities which inactivate the response. Both responses can be reversed in polarity by applied current across the cell membrane. The depolarizing response has a reversal potential of approximately +10 mv, whereas the estimated reversal potential for the hyperpolarizing response is near -70 mv. The two responses have the same spectral sensitivity function, which agrees with a Dartnall nomogram for a rhodospin with a λmax at 500 nm. It is suggested that the photochemical reactions produce different end products which give responses of opposite polarity in proximal and distal cells, or alternatively, that the reactions of the respective cell membranes to the same end product are different.
A Quantitative Description of the Dynamics of Excitation and Inhibition in the Eye of Limulus
Authors: Knight Bruce W. , Toyoda Jun-Ichi , Dodge Frederick A.
Published: May 2004

By means of intracellular microelectrode techniques, we have measured the dynamics of the several processes which translate light stimulation into spike activity in the Limulus eye. The transductions from light to voltage and from voltage to spike rate, and the lateral inhibitory transduction from spike rate to voltage, we have characterized by transfer functions. We have checked the appropriateness of treating the eye as a system of linear transducers under our experimental conditions. The response of the eye to a large spot of light undergoing sine flicker has been correctly predicted.
Cellular Inhomogeneity in Dog Red Cells As Revealed by Sodium Flux
Authors: Lange Y. , Lange R. V. , Solomon A. K.
Published: May 2004

Unidirectional 24Na fluxes across the dog red blood cell membrane were measured. The kinetics were incompatible with a single time constant but could be accounted for in terms of a two-series compartment cell model, with approximately 1% of cell Na in the outer compartment. Dog red blood cells are known to be inhomogeneous in their Na and K permeabilities. Theoretical analysis showed that such cellular inhomogeneity in the Na permeability coefficient might in principle account for the flux data. In order to evaluate the inhomogeneity effect, a technique based on the differential response of cells suspended in isosmolar high K buffers was devised to measure the variations in Na permeability in the cell population. A variation in the Na permeability coefficient of approximately 30% was found. This inhomogeneity is insufficient to account for the flux data.
Solvent Water for Electrolytes in the Muscle Fiber of the Giant Barnacle
Authors: Hinke J. A. M.
Published: May 2004

Seven experiments are described which permit estimation of the "solvent water" or the "osmotically active water" of the dissected fiber from the giant barnacle, Balanus nubilus. Each of the first four experiments includes the measurement of a free ion activity in the myoplasm by means of a Na+, K+, or Cl- ion-specific microelectrode. The fifth experiment makes use of a membrane potential vs. [K]o curve. The last two experiments measured fiber water and fiber volume as bath osmolarity was changed. The seven independent estimations of solvent water ranged from 0.64 to 0.72 of fiber water with a mean of 0.68. Since the extracellular space of single fibers was about 7% of fiber water, it was concluded that 25% of analyzable water was not acting as solvent for the osmotically active solutes in the myoplasm.
Linear Electrical Properties of the Transverse Tubules and Surface Membrane of Skeletal Muscle Fibers
Authors: Schneider Martin F.
Published: May 2004

With the use of two intracellular microelectrodes and a circuit designed to compensate for the effects of stray capacitances around the electrodes, transfer impedance measurements were made at frequencies from 0.5 to 1000 c/s on frog sartorius muscle fibers bathed in 7.5 mM K Ringer solution. Complete AC cable analyses performed at 46, 100, 215, 464, and 1000 c/s showed that the fibers behaved as ideal one-dimensional cables having purely resistive internal impedances (Ri = 102 ± 11 Ω cm). Two circuits were considered for fiber inside-outside impedance, a four lumped parameter circuit and a parallel resistance and capacitance shunted by the input impedance of a lattice model for the T-system. Least squares fits to fiber input impedance phase angles were better with the latter circuit than with the former. With the use of the lattice model the specific capacitance of both the surface and transverse tubule membranes was found to be 1 µF/cm2 and the internal resistivity of the tubules to be about 300 Ω cm.
Synaptic Electrogenesis in Eel Electroplaques
Authors: Ruiz-Manresa Francisco , Grundfest Harry
Published: May 2004

Whether evoked by neural or by chemical stimulation, the synaptic membrane of eel electroplaques contributes a depolarizing electrogenesis that is due to an increased conductance for Na and K. The reversal potential (ES) is the same for the two modes of synaptic activation. It is inside-positive by about 30–60 mv, or about midway between the emf's of the ionic batteries for Na (ENa) and K(EK). The total conductance contributed by synaptic activity (GS) varied over a fivefold range, but the individual ionic branches, GSSNa, and GSSK, change nearly equally so that the ratio GSSNa:GSSK is near unity. GSSK increases independently of the presence or absence of Na in the bathing medium, and independently of the presence or absence of the electrically excitable GK channels. When activated, the synaptic membrane appears to be slightly permeable to Ca and Mg. When the membrane is depolarized into inside positivity the conductance of the synaptic components decreases and approaches zero for large inside-positive values. Thus, the synaptic components become electrically excitable when the potential across the membrane becomes inside-positive, responding as do the nonsynaptic components, with depolarizing inactivation.
Inhibition of Impulse Activity in a Sensory Neuron by an Electrogenic Pump
Authors: Sokolove P. G. , Cooke I. M.
Published: May 2004

The crayfish tonic stretch receptor neuron manifests three phenomena: (a) Impulse frequency in response to a depolarizing current decays exponentially to half the initial rate with a time constant of about 4 sec. (b) One or more extra impulses superimposed on steady activity result in a lengthening of the interspike interval immediately following the last extra impulse which is proportional to the number of extra impulses. However, above a "threshold' number of impulses the proportionality constant becomes abruptly larger. (c) Following trains of impulses, the resting potential of the cell is hyperpolarized by an amount proportional to impulse number. Such posttetanic hyperpolarization (PTH) decays approximately exponentially with a time constant of 11 sec, but this varies with membrane potential. These effects are attributed to the incremental increase of an inhibitory (hyperpolarizing) current with a long (relative to interspike interval) decay constant. We suggest that this inhibitory current is the result of increased electrogenic Na pumping stimulated by Na entering with each impulse. Evidence is presented that the three effects are reversibly inhibited by conditions which depress active Na transport: (a) Li substituted for Na in the bath; (b) application of strophanthidin; (c) K removal; (d) treatment with cyanide; (e) cooling. We conclude that a single process is responsible for the three responses described above and identify that process as electrogenic Na pumping. Our observations also indicate that electrogenic pumping contributes to this neuron's resting potential.
The Kinetics of Sodium Extrusion in Striated Muscle As Functions of the External Sodium and Potassium Ion Concentrations
Authors: Sjodin R. A.
Published: May 2004

After a 20 min initial washout, the rate of loss of radioactively labeled sodium ions from sodium-enriched muscle cells is sensitive to the external sodium and potassium ion concentrations. In the absence of external potassium ions, the presence of external sodium ions increases the sodium efflux. In the presence of external potassium ions, the presence of external sodium ions decreases the sodium efflux. In the absence of external potassium ions about one-third of the Na+ efflux that depends upon the external sodium ion concentration can be abolished by 10-5 M glycoside. The glycoside-insensitive but external sodium-dependent Na+ efflux is uninfluenced by external potassium ions. In the absence of both external sodium and potassium ions the sodium efflux is relatively insensitive to the presence of 10-5 M glycoside. The maximal external sodium-dependent sodium efflux in the absence of external potassium ions is about 20% of the magnitude of the maximal potassium-dependent sodium efflux. The magnitude of the glycoside-sensitive sodium efflux in K-free Ringer solution is less than 10% of that observed when sodium efflux is maximally activated by potassium ions. The inhibition of the potassium-activated sodium efflux by external sodium ions is of the competitive type. Reducing the external sodium ion concentration displaces the plots of sodium extrusion rate vs. [K]o to the left and upwards.
Active Uptake of Ca++ and Ca++-Activated Mg++ ATPase in Red Cell Membrane Fragments
Authors: Cha Young N. , Shin Bak C. , Lee Kwang S.
Published: May 2004

Isolated human red blood cell membrane fragments (RBCMF) were found to take up Ca++ in the presence of ATP.1 This ATP-dependent Ca++ uptake by RBCMF appears to be the manifestation of an active Ca++ transport mechanism in the red cell membrane reported previously (Schatzmann, 1966; Lee and Shin, 1969). The influences of altering experimental conditions on Ca++-stimulated Mg++ ATPase (Ca++ ATPase) and Ca++ uptake of RBCMF were studied. It was found that pretreatment of RBCMF at 50°C abolished both Ca++ ATPase and Ca++ uptake. Pretreatment of RBCMF with phospholipases A and C decreased both Ca++ ATPase and Ca++ uptake, whereas pretreatment with phospholipase D did not significantly alter either Ca++ ATPase or Ca++ uptake. Both Ca++ ATPase and Ca++ uptake had ATP specificity, similar optimum pH's, and optimum incubation temperatures. From these results, it was concluded that Ca++ uptake is intimately linked to Ca++ ATPase.
Sodium- and Calcium-Dependent Spike Potentials in the Secretory Neuron Soma of the X-Organ of the Crayfish
Authors: Iwasaki Shizuko , Satow Youko
Published: May 2004

Membrane characteristics of neuron somata in the medulla terminalis ganglionic X-organ of crayfish have been investigated with intracellular glass microelectrodes. The soma membrane developed action potentials with 10–20 mv of overshoot. Delayed rectification appeared at 10–20 mv above resting membrane potential. In 50% of the neuron somata examined, action potentials were observed in Na-free medium or TTX medium. The peak potential level of the spike in these media depended on the extracellular concentration of Ca ion. It increased with the Ca concentration. In low calcium media, the peak potential level of the spike varied with Na concentration. Action potentials of the X-organ-sinus gland tract disappeared after bathing in Na-free or TTX medium, suggesting that the conductive action potential was dependent on Na ions. From these results, it is concluded that there are two systems in the neuron soma, one of which responds to the Na ion and the other, to the Ca ion. Inhibitory innervation of the X-organ by the cerebral ganglion was manifested by IPSP's when the optic peduncle was stimulated. A postulated connection between the Ca-dependent spike and the release of hormone in X-organ neuron somata is discussed.
Ouabain-Insensitive Sodium Movements in the Human Red Blood Cell
Authors: Sachs John R.
Published: May 2004

Red blood cells exposed to ouabain are capable of net Na outflux against an electrochemical gradient; the net outflux is inhibited by the diuretic, furosemide. In ouabain-treated cells, both the unidirectional Na outflux and the unidirectional Na influx are inhibited by furosemide. Furosemide also inhibits the ouabain-sensitive Na-Na exchange accomplished by the Na-K pump in K-free solutions. From the interaction of extracellular K, furosemide, and ouabain with the transport system, it seems possible that the ouabain-insensitive Na outflux is accomplished by the same mechanism that is responsible for the ouabain-sensitive Na-K exchange. The ouabain-insensitive Na outflux is increased by extracellular Na, and the influx increases as the intracellular Na increases. In fresh cells, high extracellular K concentrations decrease the ouabain-insensitive Na outflux and increase the ouabain-insensitive Na influx. When the rate constant for sodium outflux and the rate constant for sodium influx in ouabain-treated cells are plotted against the extracellular K concentration, the curves obtained are mirror images of each other. In starved cells, extracellular K increases the ouabain-insensitive Na outflux as does extracellular Na, and it has little effect on the Na influx.
Analysis of the Organization and Overlap of the Visual Fields in the Compound Eye of the Honeybee (Apis mellifera)
Authors: Wiitanen Wayne , Varela Francisco G.
Published: May 2004

Using the results of an optical analysis, a digital computer technique was developed to analyze the relative excitation produced by arbitrary figures at the rhabdom of the receptors of a compound eye. This technique was applied to several sets of figures for the honeybee (Apis mellifera) and a reasonable agreement was found with behavioral data. Similarly, the significance of a fixed cutoff angle for a visual field was investigated. It is concluded that overlap between neighboring ommatidia is highly significant for visual processing in the apposition eye, contrary to the assumptions of the mosaic theory.
Regulation of Tension in the Skinned Crayfish Muscle Fiber
Authors: Reuben J. P. , Brandt P. W. , Berman M. , Grundfest H.
Published: May 2004

In isolated skinned crayfish muscle fibers bathed in solutions that were buffered to be virtually free of Ca2+ (pCa 8–10) the substrate for both contraction and relaxation is the MgNTP complex. Tension increased up to 50% of the maximum capability of the fiber as the substrate MgATP increased to an optimum (pMgATP = 5.5). Relaxation was induced by further increases in MgATP. Similar bell-shaped curves of tension vs. pMgNTP were obtained with UTP and ITP, but optimum pMgUTP was about 4.5 and optimum pMgITP was about 2.6. The relation between equilibrium tension and pMgNTP is described by an equation analogous to that for the kinetics of enzymes regulated by substrate inhibition.
Mechanisms of Anion and Cation Permeations in the Resting Membrane of a Barnacle Muscle Fiber
Authors: Hagiwara S. , Toyama K. , Hayashi H.
Published: May 2004

The resting membrane of a barnacle muscle fiber is mostly permeable to cations in a solution of pH 7.7 whereas it becomes primarily permeable to anions if the pH is below 4.0. Mechanisms of ion permeation for various monovalent cations and anions were investigated at pH 7.7 and 3.9, respectively. Permeability ratios were obtained from the relationship between the membrane potential and the concentration of the test ions, and ionic conductances from current-voltage relations of the membrane. The permeability sequence for anions (SCN > I > NO3 > Br > ClO3 > Cl > BrO3 > IO3) was different from the conductance sequence for anions (Br, Cl > ClO3, NO3 > SCN). In contrast, the permeability and conductance sequences were identical for cations (K > Rb > Cs > Na > Li). The results suggest that anion permeation is governed by membrane charges while cation permeation is via some electrically neutral mechanism.
Caffeine and Excitation-Contraction Coupling in the Guinea Pig Taenia Coli
Authors: Ito Y. , Kuriyama H.
Published: May 2004

The effects of caffeine (0.2–10 mM) on the electrical and mechanical activities of guinea pig taenia coli were investigated with the double sucrose-gap method. Caffeine evoked a small tension with a latency of 20–30 sec, then phasic contraction developed and finally relaxation. The initial tension development also appeared in the Na-free solution without any marked changes in the membrane potential and membrane resistance. The phasic contraction disappeared in the Na-free solution. The relaxation in the presence of caffeine was accompanied by depolarization block of the spike generation. The minimum concentration of Ca ion needed to evoke the tension development by the caffeine was 10-7 M. Caffeine also potentiated the twitch tension below a concentration of 5 mM either in the Na-free solution or at low temperature (5°C). NO3- and Br- showed a similar response to caffeine on the potentiation of the twitch tension at low temperature.
An Analysis of Unstirred Layers in Series with "Tight" and "Porous" Lipid Bilayer Membranes
Authors: Andreoli Thomas E. , Troutman Susan L.
Published: May 2004

The present experiments were designed to evaluate the effective thickness of the unstirred layers in series with native and porous (i.e., in the presence of amphotericin B) lipid bilayer membranes and, concomitantly, the respective contributions of membranes and unstirred layers to the observed resistances to the diffusion of water and nonelectrolytes between aqueous phases. The method depended on measuring the tracer permeability coefficients for the diffusion of water and nonelectrolytes (PDDi, cm sec-1) when the aqueous phase viscosity (η) was increased with solutes having a unity reflection coefficient, such as sucrose or dextran. The effective thickness of the unstirred layers (αt, cm) and the true, or membrane, permeability coefficients for diffusion of water and nonelectrolytes (Pmmi, cm sec-1) were computed from, respectively, the slope and intercept of the linear regression of 1/PDDi on η. In both the native and porous membranes, αt was approximately 110 x 10-4 cm. The ratio of Pf, the osmotic water permeability coefficient (cm sec-1) to PmmH2O was 1.22 in the native membranes and 3.75 in the porous membranes. For the latter, the effective pore radius, computed from Poiseuille's law, was approximately 5.6 A. A comparison of Pmmi and PDDi, indicated that the porous membranes accounted for 16, 25, and 66% of the total resistance to the diffusion of, respectively, H2O, urea, and glycerol, while the remainder was referable to the unstirred layers.
Effects of Lateral Inhibition on Fluctuations of the Impulse Rate
Authors: Shapley Robert
Published: May 2004

Inhibition from neighboring eccentric cells has an effect on the variability of firing of a given eccentric cell. The reduction in the average impulse rate which is caused by inhibition decreases the variance of the impulse rate. However, this reduction of the average rate increases the coefficient of variation of the impulse rate. Inhibitory synaptic noise should add to the low frequency portion of the variance spectrum of the impulse rate. This occurs because of the slow time course of inhibitory synaptic potentials. As a consequence, inhibition decreases the signal-to-noise ratio for low frequency modulated stimuli.
Studies on the Electrical Potential Profile across Rabbit Ileum
Authors: Rose Richard C. , Schultz Stanley G.
Published: May 2004

When isolated strips of mucosal rabbit ileum are bathed by physiological electrolyte solution the electrical potential difference (PD) across the brush border (ψmc) averages 36 mv, cell interior negative. Rapid replacement of Na in the mucosal solution with less permeant cations, Tris or choline, results in an immediate hyperpolarization of ψmc. Conversely, replacement of choline in the mucosal solution with Na results in an abrupt depolarization of ψmc. These findings indicate that Na contributes to the conductance across the brush border. The presence of actively transported sugars or amino acids in the mucosal solution brings about a marked depolarization of ψmc and a smaller increase in the transmural PD (Δψms). It appears that the Na influx that is coupled to the influxes of amino acids and sugars is electrogenic and responsible for the depolarization of ψmc. Under control conditions Δψms can be attributed to the depolarization of ψmc together with the presence of a low resistance transepithelial shunt, possibly the lateral intercellular spaces. However, quantitatively similar effects of amino acids on ψmc are also seen in tissues poisoned with metabolic inhibitors or ouabain. Under these conditions Δψmc is much smaller than under control conditions. Thus, the depolarization of ψmc might not account for the entire Δψms, observed in nonpoisoned tissue. An additional electromotive force which is directly coupled to metabolic processes might contribute to the normal Δψms.
Hydroxyl Ion Movements across the Human Erythrocyte Membrane
Authors: Crandall E. D. , Klocke R. A. , Forster R. E.
Published: May 2004

A stopped flow rapid reaction apparatus capable of following changes of ±0.02 pH unit in 0.1 ml of solution in less than 0.005 sec has been developed, utilizing a commercially available pH-sensitive glass electrode. Using this instrument, extracellular pH at 37°C was followed from less than 0.025 sec to 300 sec after mixing equal volumes of the following CO2-free solutions: (A) normal human red cells, washed three times and resuspended in 150 mM NaCl at pH 7.2 with a hematocrit of 18%; and, (B) 150 mM NaCl adjusted with HCl or NaOH to pH 2.1 to pH 10.3. A minimum of 2 ml of mixture had to flow through the electrode chamber to ensure complete washout. The mixing process produced a step change in the pH of the extracellular fluid, after which exchanges across the red cell membrane and buffering by intracellular hemoglobin caused it to return toward pH 7.2 with an approximately exponential time course. Under the assumption that pH changes after mixing represent exchanges of hydroxyl for chloride ions across the cell membrane, hydroxyl ion permeabilities (POH- in cm/sec) were calculated and found to vary from 2 x 10-4 at pH 9 to 4 x 10-1 at pH 4 according to the empirical relationship POH- = 170 exp (-1.51 pH). The form of the dependence of POH- on extracellular pH does not appear compatible with a simple fixed charge theory of membrane permselectivity.
The Effect of Norepinephrine and Dibutyryl Cyclic Adenosine Monophosphate on Cation Transport in Duck Erythrocytes
Authors: Riddick D. H. , Kregenow F. M. , Orloff J.
Published: May 2004

Freshly prepared duck erythrocytes, incubated either in plasma or an isotonic synthetic medium containing norepinephrine ([K] of both media ∼ 2.5 mM), maintain water and electrolyte composition in the steady state (upper steady state) for at least 90 min. If incubated in the synthetic medium without norepinephrine or in plasma to which a ß-adrenergic blocking agent (propranolol) is added, the cells lose both water and electrolyte (predominantly KCl) until a new steady state is reached (lower steady state). Reaccumulation of water and electrolyte from isotonic solutions toward the upper steady-state levels requires the addition of norepinephrine and KCl. Reaccumulation is maximal when the concentration of K and norepinephrine in the medium is 15 mM and 10-7 M, respectively. Dibutyryl cyclic-AMP (10-2 M) mimics norepinephrine in lower steady-state cells. Although an analogous effect in upper steady-state cells was not established with certainty, it is proposed that the catecholamine-induced net changes in water and electrolyte movement in duck erythrocytes are a consequence of stimulation of the activity of a membrane-bound adenyl cyclase system.
Dynamics of Excitation and Inhibition in the Light-Adapted Limulus Eye in situ
Authors: Biederman-Thorson Marguerite , Thorson John
Published: May 2004

The dynamics of spike discharge in eccentric cell axons from the in situ lateral eye of Limulus, under small sinusoidal modulation of light to which the eye is adapted, are described over two decades of light intensity and nearly three decades of frequency. Steady-state lateral inhibition coefficients, derived from the very low-frequency response, average 0.04 at three interommatidial spacings. The gain vs. frequency of a singly illuminated ommatidium is described closely from 0.004 to 0.4 cps by the linear transfer function s0.25; this function also accounts approximately for the measured phase leads, the small signal adaptation following small step inputs, and for Pinter's (1966) earlier low-frequency generator potential data. We suggest that such dynamics could arise from a summation in the generator potential of distributed intensity-dependent relaxation processes along the dendrite and rhabdome. Analysis of the dynamic responses of an eccentric cell with and without simultaneously modulated illumination of particular neighbors indicates an effect equivalent to self-inhibition acting via a first-order low-pass filter with time constant 0.42 sec, and steady-state gain near 4.0. The corresponding filters for lateral inhibition required time constants from 0.35 to 1 sec and effective finite delay of 50–90 msec.
The Effect of Low-Level Activation on the Mechanical Properties of Isolated Frog Muscle Fibers
Authors: Lännergren J.
Published: May 2004

The mechanical properties, as revealed by minute length changes, of isolated twitch fibers of the frog have been studied at rest and during low-level activation. Resting tension is 77 ± 23 mN/cm2 (mean ± SD) at 2.2 µm sarcomere length.1 The slope of the tension curve (ΔP/ΔL) recorded during a constant-speed length change of a resting fiber is initially large. At length changes exceeding about 0.18 % of the initial length of the fiber ΔP/ΔL falls abruptly and remains close to zero during the rest of the length change. The amplitude of the tension response is reduced after a length change and returns to normal in about 3 min. Hypertonic sucrose-Ringer solutions cause a small, maintained rise in tension up to 1.4–1.6 times normal osmotic strength. Higher sucrose concentrations cause relatively large, transient tension responses. The initial ΔP/ΔL is increased in moderately hypertonic solutions; it may be reduced in more strongly hypertonic solutions. Elevated [K]o (range 10–17.5 mM) causes a marked reduction in ΔP/ΔL. In this range of [K]o the reduction is not accompanied by changes in resting tension. Addition of 1–1.5 mM caffeine to the Ringer solution affects the resting tension very little but also reduces ΔP/ΔL. The results suggest that stiffness and tension development are not related in a simple way.
Chemical Modification of Membranes
Authors: Knauf Philip A. , Rothstein Aser
Published: May 2004

Four different amino-reactive reagents, 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid (SITS),1 1-fluoro-2,4-dinitrobenzene (FDNB), 2,4,6-trinitrobenzene sulfonic acid (TNBS), and 2-methoxy-5-nitrotropone (MNT) decrease the anion permeability of the human red blood cell, as measured by sulfate fluxes, whereas the sulfhydryl agent, parachloromercuriphenyl sulfonic acid (PCMBS), does not. In contrast, PCMBS increases the cation permeability as measured by K+ leakage, whereas SITS does not. Of the other agents, FDNB increases the cation permeability to the same extent as PCMBS but MNT and TNBS produce smaller increases. PCMBS does not protect against FDNB as it does against other sulfhydryl agents (X-irradiation) and the FDNB effect on cations is attributed to amino groups. Studies of the binding of SITS indicate that it does not penetrate into the membrane and its failure to influence cation permeability is attributed to its inability to reach an internal population of amino groups. It is concluded that two ion permeability barriers, both involving proteins, are present in the red blood cell. The more superficial barrier contains amino groups and controls anion flow; the more internal barrier contains sulfhydryl and amino groups and controls cation flow. The amino groups contribute to the control of permeability by virtue of their positive charges, but the role of sulfhydryl groups is not clear. Only a small fraction of the membrane protein amino and sulfhydryl is involved in the barriers.
Chemical Modification of Membranes
Authors: Knauf Philip A. , Rothstein Aser
Published: May 2004

The amino-reactive reagent, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS),1 considerably reduces the uptake of the sulfhydryl agent, parachloromercuriphenylsulfonic acid (PCMBS), but does not reduce its effects on cation permeability and on cation transport. These data indicate that PCMBS enters the membrane by at least two channels, one sensitive and the other insensitive to SITS, with only the latter leading to the cation-controlling sulfhydryl groups. Substitution of phosphate or sulfate for chloride results in an inhibition of PCMBS uptake via the SITS-insensitive pathway. These and other data lead to the conclusion that the SITS-sensitive pathway is the predominant one for anion permeation, and the insensitive one for cation permeation. Parachloromercuribenzoate (PCMB), an agent that is more lipid-soluble than PCMBS, penetrates faster but has a smaller effect on cation permeability. Its uptake is less sensitive to SITS. These and other observations suggest that the cation permeation path involves an aqueous channel in the membrane.
Tracer Determinations of Human Red Cell Membrane Permeability to Small Nonelectrolytes
Authors: Savitz David , Solomon A. K.
Published: May 2004

A flow system has been used to determine the permeability of human red cell membranes to four small nonelectrolytes labeled with 14C. The permeability coefficients, ω, in units of mol dyne-1 sec-1 x 1015, are: ethylene glycol, 6; urea, 13; formamide, 22; and methanol, 131. The values for urea and formamide are in good agreement with values obtained by Sha'afi, Gary-Bobo, and Solomon by the minimum method. The unusually high value for ω for methanol is ascribed to its solubility in the red cell membrane since its ether: water partition coefficient is 0.14, higher by more than an order of magnitude than the ether: water partition coefficient for water. The other three solutes are hydrophilic and are characterized by values of ω which behave consistently with those of other hydrophilic amides and ureas. The values of ω for the three hydrophilic solutes measured are also consistent with an equivalent pore radius of about 3.5 A in agreement with previous estimates made on the basis of other types of studies.
A Stochastic Model for Discrete Waves in the Limulus Photoreceptor
Authors: Srebro Richard , Behbehani Mahmood
Published: May 2004

A stochastic model that links the absorption of a photon to the production of a discrete wave in the photoreceptor of the lateral eye of Limulus is proposed. By separating a discrete wave into an initial component due directly to the absorption of a photon, and a second quasi all-or-nothing component, a mathematical description of the latencies of discrete waves is deduced and some important features of their time courses are suggested. The predictions of the model are compared to observations from 60 different ommatidia.
Effect of Calcium, Temperature, and Polarizing Currents upon Alternating Current Excitation of Space-Clamped Squid Axons
Authors: Guttman Rita , Hachmeister Lon
Published: May 2004

Alternating current threshold excitation of space-clamped squid giant axons was measured as a function of frequency, external calcium concentration, temperature (from 10° to 35°C), and hyper- and depolarizing steps. In normal axons there is usually an optimum frequency at about 120 Hz, at which the threshold is a minimum. The threshold rises at both lower and higher frequencies to give a resonance curve. Low calcium causes an increase in optimum frequency, a decrease in current threshold, and an increase in sharpness of tuning in both real axons and axons computed according to the Hodgkin-Huxley formulation; high calcium causes opposite effects. An increase in temperature causes an increase of optimum frequency, an increase in sharpness of tuning, and an increase in threshold current in both real and computed axons. The Q10 for the effect of temperature upon optimum frequency is 1.8 in real and computed axons at moderate temperatures. Hyperpolarization causes (a) a decrease in optimum frequency, (b) a decrease in sharpness of tuning, and (c) an increase in threshold. Depolarization causes opposite effects.
The Response of Duck Erythrocytes to Hypertonic Media
Authors: Kregenow Floyd M.
Published: May 2004

The addition of a hypertonic bathing medium to duck erythrocytes results in an initial instantaneous phase of osmotic shrinkage and, when the [K]o of the hypertonic solution is larger than "normal," in a second, more prolonged phase, the volume regulatory phase. During the latter, which also requires extracellular Na, the cells swell until they approach their initial isotonic volume. The increase in cell volume during the volume regulatory phase is accomplished by a gain in the cell content of K, Cl, and H2O. There is also a smaller increase in the Na content of the cell. Potassium is accumulated against an electrochemical gradient and is therefore actively transported into the cell. This accumulation is associated with an increase, although dissimilar, in both K influx and efflux. 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 response is independent of any effect of norepinephrine. The changes in cell size during the volume regulatory phase are discussed as the product of a volume controlling mechanism identical in principle to the one reported in the previous paper which controls cell volume in hypotonic media. Similarly, this mechanism can regulate cell size, when the Na-K exchange, ouabain-inhibitable pump mechanism is blocked.
Interaction of Tetraethylammonium Ion Derivatives with the Potassium Channels of Giant Axons
Authors: Armstrong Clay M.
Published: May 2004

A number of compounds related to TEA+ (tetraethylammoniumion) were injected into squid axons and their effects on gK (the potassium conductance) were determined. In most of these ions a quaternary nitrogen is surrounded by three ethyl groups and a fourth group that is very hydrophobic. Several of the ions cause inactivation of gK, a type of ionic gating that is not normally seen in squid axon; i.e., after depolarization gK increases and then spontaneously decreases to a small fraction of its peak value even though the depolarization is maintained. Observations on the mechanism of this gating show that (a) QA (quaternary ammonium) ions only enter K+ channels that have open activation gates (the normal permeability gates). (b) The activation gates of QA-occluded channels do not close readily. (c) Hyperpolarization helps to clear QA ions from the channels. (d) Raising the external K+ concentration also helps to clear QA ions from the channels. Observations (c) and (d) strongly suggest that K+ ions traverse the membrane by way of pores, and they cannot be explained by the usual type of carrier model. The data suggest that a K+ pore has two distinct parts: a wide inner mouth that can accept a hydrated K+ ion or a TEA+-like ion, and a narrower portion that can accept a dehydrated or partially dehydrated K+ ion, but not TEA+.
Active Sodium and Potassium Transport in High Potassium and Low Potassium Sheep Red Cells
Authors: Hoffman P. G. , Tosteson D. C.
Published: May 2004

The kinetic characteristics of the ouabain-sensitive (Na + K) transport system (pump) of high potassium (HK) and low potassium (LK) sheep red cells have been investigated. In sodium medium, the curve relating pump rate to external K is sigmoid with half maximal stimulation (K1/2) occurring at 3 mM for both cell types, the maximum pump rate in HK cells being about four times that in LK cells. In sodium-free media, both HK and LK pumps are adequately described by the Michaelis-Menten equation, but the K1/2 for HK cells is 0.6 ± 0.1 mM K, while that for LK is 0.2 ± 0.05 mM K. When the internal Na and K content of the cells was varied by the PCMBS method, it was found that the pump rate of HK cells showed a gradual increase from zero at very low internal Na to a maximum when internal K was reduced to nearly zero (100% Na). In LK cells, on the other hand, no pump activity was detected if Na constituted less than 70% of the total (Na + K) in the cell. Increasing Na from 70 to nearly 100% of the internal cation composition, however, resulted in an exponential increase in pump rate in these cells to about ⅙ the maximum rate observed in HK cells. While changes in internal composition altered the pump rate at saturating concentrations of external K, it had no effect on the apparent affinity of the pumps for external K. These results lead us to conclude that the individual pump sites in the HK and LK sheep red cell membranes must be different. Moreover, we believe that these data contribute significantly to defining the types of mechanism which can account for the kinetic characteristics of (Na + K) transport in sheep red cells and perhaps in other systems.
Physiological Studies During Formation and Development of Rat Neuromuscular Junctions in Tissue Culture
Authors: Robbins Norman , Yonezawa Takeshi
Published: May 2004

Developing neuromuscular junctions in tissue cultures of rat embryo spinal cord and muscle were studied with intracellular recording. Excitatory junctional potentials (ejps) were found during nerve or spinal cord stimulation, and also arising spontaneously. The time-course of the potentials tended to be shorter in cultures older than 9 days in vitro than in more recently innervated cultures. Evidence of multiple innervation was found in many cells. In order to test the hypothesis that transmitter was released in integral multiples of a quantal amount and according to a Poisson distribution, mean quantum content was calculated from the coefficient of variation of ejp amplitudes, the percentage of zero responses, and the ratio of mean amplitude to mean of the smallest class of amplitudes. The three independent measures were in fair or good mutual agreement, implying that the mechanism of transmitter release in newly developed junctions is the same as in the adult. In newly formed junctions, ejps were subthreshold for action potential generation, but afterwards mean quantum content increased and action potentials were generated by single ejps. In fibers developing both with and without innervation, the entire muscle cell surface was as sensitive to acetylcholine as the adult end plate region. Innervation was related to cross-striation: every cross-striated fiber tested was found to be innervated, and denervation in vitro led to loss of distinct cross-striations.