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PubMed1979

Membrane potential oscillations in molluscan "burster" neurones.

Membrane potential oscillations can be induced in molluscan neurones under a variety of artificial conditions. In the so-called 'burster' neurones oscillations are generated even in isolated cells. A likely mechanism for 'bursting' involves the following ionic currents: 1. A transient inward current carried by Na+ and Ca2+. This current is responsible for the upstroke of the action potentials. 2. A delayed outward current carried by K+. This current is voltage-sensitive and is responsible for the downstroke of the action potential during the early part of the burst. It becomes progressively inactivated during the burst. Its amplitude depends on the intracellular pH. 3. A rapidly developing outward current carried by K+ which is inactivated at potentials close to action potential threshold. This current tends to hold the membrane in the hyperpolarized state and is involved in spacing the action potentials. 4. A prolonged inward current which may not inactivate. It is probably carried by both Na+ and Ca2+. This current is responsible for the depolarizing phase of the burst but also contributes to the action potential. 5. A slowly developing outward current, carried by K+. This current appears as a result of a slow increase in intracellular ionized calcium and is responsible for the hyperpolarizing phase of the burst. Note that a transient increase in this current may also contribute to the falling phase of the action potential during the later stages of the burst. It is also sensitive to intracellular pH. One of the more significant features of this system of producing membrane potential oscillations is that the frequency of the bursts depends on the rate at which the intracellular ionized calcium returns to its resting level. This process depends on the metabolic state of the animal which can thereby exert a considerable influence on the electrical activity of burster neurones.

Animals↗
PubMed1978

Changes in membrane potential during calcium ion influx and efflux across the mitochondrial membrane.

1. A depolarisation of the membrane of rat liver mitochondria, as measured with the safranine method, is seen during Ca2+ uptake. The depolarisation is followed by a slow repolarisation, the rate of which can be increased by the addition of EGTA or phosphate. 2. Plots relating the initial rate of calcium ion (Ca2+) uptake and the decrease in membrane potential (delta psi) to the Ca2+ concentration show a half-maximal change at less than 10 micron Ca2+ and a saturation above 20 micron Ca2+. 3. Plots relating the initial rate of Ca2+ uptake to delta psi are linear. 4. Addition of Ca2+ chelators, nitriloacetate or EGTA, to deenergized mitochondria equilibrated with Ca2+ causes a polarisation of the mitochondrial membrane due to a diffusion potential created by electrogenic Ca2+ efflux. 5. If the extent of the response induced by different nitriloacetate concentrations is plotted against the expected membrane potential a linear plot is obtained up to 70 mV with a slope corresponding to two-times the extent of the response induced by valinomycin in the presence of different potassium ion gradients. This suggests that the Ca2+ ion is transferred across the membrane with one net positive charge in present conditions.

Acetates↗
PubMed1978

Erythrocyte membrane potentials determined by hydrogen ion distribution.

If the extracellular fluid is left unbuffered, dynamic membrane potential changes in the red blood cell may be determined from external pH readings. For some types of experiments it is necessary to accelerate H+ equilibration by adding minute amounts of hydrogen carriers. The method is independent of hematocrit over a wide range of membrane potential changes. Membrane potential jumps produced by permeability changes or by changes in ionic composition may be measured. The method provides a convenient means of measuring parameters of both the conductive and non-conductive anion pathways in the red cell.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1977

The effects of gastrin and gastrin analogues on pancreatic acinar cell membrane potential and resistance.

1 Intracellular recordings of membrane potentials and input resistance have been made from the exocrine acinar cells of mouse and rat pancreas placed in a tissue bath perfused with Krebs-Henseleit solution.2 The resting acinar cell membrane potential was about -38 mV. The acinar cells were stimulated by cholecystokinin-pancreozymin (CCK-PZ), gastrin and the gastrin-related polypeptides, caerulein and desulphated caerulein. The immediate effect of stimulation with these secretagogues was always a depolarization and a concomitant reduction in input resistance and time constant. Depolarization of the acinar cell membrane by these secretagogues was not abolished in the presence of atropine (1.4 muM).3 These peptide secretagogues were divided into the gastrin group and the CCK-PZ group according to the time course of the depolarizations and the shape of the dose-response curve. The depolarization evoked by the gastrin group returned quickly to the resting level but that evoked by the CCK-PZ group was long lasting. The time course and the dose-response curve for desulphated caerulein was identical with that of gastrin.4 It was confirmed electrophysiologically that the activity of gastrin is exerted by the C-terminal tetrapeptide; but the activity of caerulein depends on the C-terminal heptapeptide, especially the presence in the molecule of the sulphated tyrosyl residue at position 7 (numbering from the C-terminus). The equivalent sulphated tyrosyl residue in CCK-PZ is probably necessary for optimal activity of this polypeptide.5 The dose-response curves obtained by electrophysiological methods indicated that the relative potencies of the peptides on mouse pancreatic acinar cells were caerulein > CCK-PZ > gastrin. Synthetic human gastrin I was found to have a higher potency than either tetra- or pentagastrin.

Acetylcholine↗
PubMed1978

Membrane potential of spinal motoneurons during natural sleep in cats.

The membrane potential of spinal motoneurons was recorded during wakefulness, NREM sleep, and REM sleep in minimally restrained, behaving cats. At the onset of sleep, the membrane potential generally increased in polarization in rough proportion to time spent asleep. During the postural atonia of REM sleep, the membrane potential of all motoneurons was tonically hyperpolarized. Antecedents of NREM sleep electromyographic suppressions, and REM sleep myoclonic twitches were seen as transient hyperpolarizations and depolarizations, respectively.

Animals↗
PubMed1979

Optical probe responses on sarcoplasmic reticulum: oxacarbocyanines as probes of membrane potential.

The relationship between Ca2+ fluxes and the ion diffusion potential was analyzed on sarcoplasmic reticulum membranes using oxacarbocyanine dyes as optical probes for membrane potential. 3.3'-Diethyloxodicarbocyanine responds to ATP-induced Ca2+ uptake by isolated sarcoplasmic reticulum vesicles with a decrease in absorbance at 600 nm. The optical change is reversed during Ca2+ release from sarcoplasmic reticulum induced by KCl or by ADP and inorganic phosphate. The absorbance changes are largely attributable to the binding of accumulated Ca2+ to the membrane. There is no indication that sustained changes in membrane diffusion potential would accompany pump-mediated Ca2+ fluxes. A large change in the absorbance of 3,3'-diethyloxodicarbocyanine was observed on sarcoplasmic reticulum vesicles under the influence of membrane potential generated by valinomycin in the presence of a K+ gradient or by ionophore A23187 in the presence of a Ca2+ gradient. The maximum of the potential-dependent absorbance change is at 575--580 nm. The potentials generated by valinomycin or ionophore A23187 are short-lived due to the high permeability of sarcoplasmic reticulum membranes for cations and anions. There is no correlation between the direction and magnitude of the artifically imposed membrane potential and the rate of Ca2+ uptake or release by isolated sarcoplasmic reticulum vesicles.

Adenosine Triphosphate↗
PubMed1979

Characteristics of fast excitatory postsynaptic current in bullfrog sympathetic ganglion cells. Effects of membrane potential, temperature and Ca ions.

The membrane current underlying the fast excitatory postsynaptic potential (EPSC) of bullfrog sympathetic ganglion cells was studied. The relationship between the EPSC amplitude and membrane potential was linear at negative levels of membrane potential, but deviated from the linearity toward a smaller amplitude at positive levels. The falling phase of EPSC almost followed a single exponential decay. The half-decay time (HDT) of EPSC's increased exponentially with an increase in the negativity of membrane potential. The rise time (RT) was also prolonged slightly with membrane hyperpolarization. Lowering of temperature decreased the EPSC amplitude, lengthened markedly the HDT and increased the slope relating the logarithm of the HDT to membrane potential. Neostigmine (1 x 10(-5) M) prolonged both the RT and HDT. A decrease in Ca2+ concentration caused a marked reduction in the EPSC amplitude, and a slight shortening in the RT and HDT. An increase in Ca2+ concentration significantly prolonged the RT and HDT without altering the slope of the relationship between the HDT and membrane potential, while the amplitude of EPSC was increased slightly. The HDT was independent of EPSC amplitude. It is suggested that the mechanism responsible for closing the ion channels of the nicotinic receptor at the subsynaptic membrane is regulated by membrane potential. The possible mechanisms of the action of Ca2+ on the decay phase of EPSC were discussed.

Animals↗
PubMed1979

Requirement for membrane potential in active transport of glutamine by Escherichia coli.

The effect of reducing the membrane potential on glutamine transport in cells of Escherichia coli has been investigated. Addition of valinomycin to tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetic acid-treated E. coli cells in the presence of 20 mM exogenous potassium reduced the membrane potential, as measured by the uptake of the lipophilic cation triphenylmethylphosphonium, and caused a complete inhibition of glutamine transport. Valinomycin plus potassium also caused a rapid decrease in the intracellular levels of ATP of normal E. coli cells, but had little if any effect on the ATP levels of two mutants of E. coli carrying lesions in the energy-transducing ATP complex (unc mutants). Yet both the membrane potential and the capacity to transport glutamine were depressed in the unc mutants by valinomycin and potassium. These findings are consistent with the hypothesis that both ATP and a membrane potential are essential to the active transport of glutamine by E. coli cells.

Adenosine Triphosphatases↗
PubMed1978

Ionic effects on the membrane potential of hyperpolarizing photoreceptors in scallop retina.

1. The effects of different external ionic conditions and of metabolic inhibitors on the membrane potential of hyperpolarizing photoreceptors in the retina of the scallop Pecten irradians were examined in the presence and absence of light.2. Changes in extracellular K(+) have a greater effect on membrane potential in the light than in darkness. The receptor potential is increased in amplitude when [K](o) is reduced and decreased when [K](o) is elevated. It is hyperpolarizing when [K](o) is less than the estimated value for [K](i) and depolarizing when this condition is reversed.3. The complete replacement of [Na](o) causes a significant hyperpolarization of membrane potential in darkness, whereas it has a much smaller hyperpolarizing effect on the peak of the receptor potential.4. The ratio of Na(+) to K(+) permeabilities (P(Na)/P(K)) decreases during bright illumination. Our results suggest that P(K) is seven times that for P(Na) in the dark but is 57 times greater than P(Na) in light.5. The metabolic inhibitors DNP and NaCN cause membrane potential in the dark to hyperpolarize. This hyperpolarization is associated with a decrease in the P(Na)/P(K) ratio similar to that found during illumination.6. High [Ca(+)](o) also causes membrane potential in the dark to hyperpolarize. This hyperpolarization is associated with an increase in membrane conductance.7. The results indicate that the hyperpolarizing receptor potential of the distal photoreceptor is produced by a light-evoked increase in K(+) permeability.

Animals↗
PubMed1979

Further studies of the membrane potential of the stria cells of the guinea pig in vitro.

Negative membrane potentials from the stria vascularis of the guinea pig have been recorded in vivo. Stable negative membrane potentials from the stria cells have also been recorded for as long as 2 minutes in vitro. They varied from -20 mV to -49 mV, irrespective of whether the stria vascularis was immersed in Ringer's solution for in K-Ringer's solution (approximately to the composition of an endolymph). Labelling of the inserted stria cells from which the membrane potential had been recorded demonstrated that the microelectrode tip was inside the cell. These cells will continue to show electrical activity for some time when immersed in suitable media.

Animals↗
PubMed1978

Effects of X-rays on cell membranes. I. Changes of membrane potential of L-cells.

Changes in the membrane potential of cultured L-929lcells were investigated after irradiation with doses ranging from 5-200 Gy. Immediately after irradiation a depolarisation is observed that is followed by a damped oscillation of the membrane potential and finally by a rapprochement to the control value. Whereas the magnitude of depolarisation does not show any dependence on irradiation dose, the time required to reach the control value again increases with increasing dose. Up to 10 Gy, the period of the first half-oscillation rises rapidly to about 12 min, at higher doses a slow linear increase follows reaching a value of 23 min after 200 Gy.

Cell Membrane↗
PubMed1979

Estimation of membrane potentials of individual lymphocytes by flow cytometry.

The membrane potentials of individual cells can be estimated by flow cytometric quantitation of the cells' uptake of the fluorescent lipophilic cationic dye 3,3'-dihexyloxacarbocyanine iodide. Human lymphocytes separated from peripheral blood on Hypaque-Ficoll gradients are uniformly depolarized by gramicidin and hyperpolarized by valinomycin. Concanavalin A and phytohemagglutinin depolarize only a fraction of the lymphocytes. The flow cytometric technique allows precise detection of heterogeneous membrane potential responses to stimuli such as lectins; it could also provide a basis for sorting cells that respond differently to a given stimulus.

Cations↗
PubMed1976

Concentration dependence of the veratrine effect on inducing depolarization and membrane potential oscillation in skeletal muscle.

The concentration dependence of the effect of veratrine in inducing depolarization and membrane potential oscillation in the frog sartorius muscle has been studied. (1) On increasing the veratrine concentration from 0.025 to 1 mM, the latency period of the development of membrane potential oscillation and depolarization is proportionally shortened. (2) On changing the veratrine concentration from 0.025 to 1 mM, the magnitude of depolarization is raised logarithmically. (3) When the veratrine concentration reaches 0.05-0.1 mM, both the amplitude and the frequency of the membrane potential oscillation increase. On rising to 1 mM, a further increase in frequency to eight-fold occurs especially in the later phase of oscillation. At this concentration range, the amplitude of oscillation inversely proportional to the concentration of veratrine. (4) On increasing the veratrine concentration above 0.1 mM, the membrane potential oscillation ceases after a temporary rise of frequency. This inhibitory effect of veratrine is, however, reversible, and oscillations appear again, despite the absence of veratrine in Ringer's solution. This also proves the persistance of the veratrine effect.

Animals↗
PubMed1977

Oscillations of membrane potential in L cells. I. Basic characteristics.

The membrane potentials and resistances of L cells were measured using a standard electrophysiological technique. The values obtained in physiological media were around--15 mV and 37Momega, respectively. Almost all the large nondividing L cells (giant L cells) showed spontaneous oscillations of the membrane potential between around -15 and -40 mV. Application of an appropriate electrical or mechanical stimulus was also capable of eliciting responses but such were usually induced only once. The total membrane conductance increased significantly and in parallel with such a hyperpolarizing response. Cooling of the cells and application of metabolic inhibitors to the cells completely blocked the spontaneous oscillation despite the fact that the electrically induced hyperpolarizing response remained. Intracellular K+, Na+ and Cl- concentrations were measured by means of a flame photometer and a chloridometer, and the equilibrium potential for each ion was estimated.

Acetylcholine↗
PubMedDate not supplied

[Role of phospholipids in the generation of membrane potentials by proteoliposomes].

Closed protein-phospholipid particles (proteoliposomes), obtained by self-assembly method, are capable to generate and to maintain the membrane potential in the case if their protein complex is represented by: a) a complex of mitochondrial ATPase; b) a complex of cytochrome oxidase and cytochrome c and c) bacteriorhodopsin from Halobacterium halobium; and their phospholipid component is represented by phosphatidylethanolamine or by a mixture of mitochondrial phospholipids. Only cytochromoxidase and bacteriorhodopsin (but not ATPase) proteoliposomes with phosphatidylserine are active. Cardiolipin also is not active in experiments with ATPase. Phosphatidylcholine produces in all the cases proteoliposomes incapable of maintaining the membrane potential. It is concluded that the inefficiency of phosphatidylcholine in the formation of proteoliposomes, generating the membrane potential, is due to the impossibility of obtaining closed membrane forms with a high electric resistance. The inefficiency of phosphatidylserine and cardiolipine, in the case of ATPase protein component of proteoliposomes, may be due to a specific requirement of this generator of the membrane potential in phosphatidylethanolamine.

Adenosine Triphosphatases↗
PubMed1979

Optical probes of membrane potential in heart muscle.

1. The fluorescent dye Merocyanine-540 and the two weakly fluoresecnet dyes Merocyanine-rhodanine and Merocyanine-oxazolone are shown to respond as optical probes of membrane potential in heart muscle. 2. In frog hearts stained with Merocyanine-540, the absorption at 540 nm decreases by 0.1-1.0% and increase at 570 nm excitation wave-length, the fluorescence increases by 1-2%. The time course of all three optical measurements follows the kinetics of the action potential. 3. Merocyanine-rhodanine exhibits potential-dependent optical responses through a 0.5% decrease in absorption at 750 nm, and Merocyanine-oxazolone has a 1.0% decrease in absorption at 720 nm. Their optical responses have a signal-to-noise ratio of 100/1 and 500/1, respectively. 4. The action spectrum of Merocyanine-rhodanine is triphasic in frog heart with an increase in transmittance from 780 to 700, a decrease from 700 to 600, and increase from 600 to 450 nm. Merocyanine-oxazolone shows only increases in transmittance during membrane depolarization. 5. The optical responses of these probes are linear with respect to changes in membrane potential. 6. Pharmacological agents or ionic interventions do not alter the membrane potential sensitivity of Merocyanine-540. 7. Rapid spectrophotometric measurements at various phases of the action potential indicate that the potential dependent optical signals of Merocyanine-540 are produced by changes in amplitude of fluorescence and absorption bands. The lack of wave-length displacement as a function of membrane potential, i.e. electrochromism, is not the mechanism governing the voltage sensitivity of Merocyanine-540. 8. The data suggest that these Merocyanine dyes bind to the plasma membrane and serve as linear optical probes of membrane potential in heart muscle.

Animals↗
PubMed1975

Membrane potential and conductance during pinocytosis induced in Amoeba proteus with alkali metal ions.

An investigation of the relationship between the polarized state of the membrane and the onset and the intensity of pinocytosis was made in Amoeba proteus. Membrane potential and input resistance was in all instances found to decrease in approximate proportion to the number of channels when pinocytosis was induced by a variety of alkali metal ions at varying pH. Channels began to appear when the membrane was depolarized to -30 mV by the inducer of pinocytosis. With all inducers the maximum pinocytosis was encountered at membrane potentials close to zero. No positive potentials were recorded when the chloride salts of the inducing cations were used. At high concentrations of alkali ions a transient increase of the chloride permeability caused short-lasting hyperolarizations of the membrane. Inhibition of pinocytosis by Ca++ was accompanied by an increase of input resistance and membrane potential. The selectivity of the membrane to different alkali metal ions observed as changes in pinocytosis intensity, membrane potential and input resistance was found to vary with the concentration of the inducer and with the Ca++ concentration of the extracellular solution. Displacement of membrane bound Ca++ appeared to decrease the field strength of charged groups in the membrane altering its selectivity among alkali cations. The formation of pinocytotic channels is suggested to require translocation of Ca++ from the membrane into the cell and would therefore be closely related to the electrical properties of the amoeba.

Alkalies↗
PubMed1975

Acid-base changes and excitation-contraction coupling in rabbit myocardium. II. Effects on resting membrane potential, action potential characteristics and propagation velocity.

The effects of changes in acid-base parameters on the resting membrane potential, action potential characteristics and propagation velocity were studied in isolated rabbit papillary muscles. Lowering extracellular pH from 7.4 to 6.7 in a bathing solution buffered with 10 mM histidine did not alter the resting membrane potential or action potential characteristics but casused slight reduction in propagation velocity. A parallel increase in HCO3-minus concentration (up to 47 mM)and PCO2 at a constant extracellular pH of 7.4 caused a substantial decrease in action potential duration but did not alter the resting membrane potential or propagation velocity. The decrease in action potential duration was caused by the increase in HCO3-minus concentration. Propionate (47nM) caused a shortening of the action potential which was of the same magnitude as for HCO3-minus but methylsulfate (47nM) did not have this effect. The possible influence of these changes on the inotropic state of the myocardium and the cellular mechanisms involved are discussed.

Action Potentials↗