PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Membrane Potentials”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1976

Change in zeta potential and membrane potential of slime mold Physarum polycephalum in response to chemical stimuli.

Electrophoretic study of microplasmodia of the true slime mold Physarum polycephalum was carried out in the presence of various concentrations of inorganic salts, nucleotides and sugars, and the zeta potential at the surface of the plasmodia was determined from the electrophoretic mobilities. The membrane potential of the plasmodia was also measured under the same external conditions. It was shown that changes in the membrane potential induced by the chemical stimuli agreed approximately with those induced in the zeta potential in all cases examined. These results suggested that the phase boundary potential at the membrane-solution interface is mainly responsible for the membrane potential in the chemoreception of the slime mold.

Adenosine Triphosphate↗
PubMed1976

Adenosine 5'-triphosphate synthesis energized by an artificially imposed membrane potential in membrane vesicles of Escherichia coli.

Adenosine 5'-triphosphate (ATP) synthesis driven by an artificially imposed membrane potential in right-side-out membrane vesicles of Escherichia coli was investigated. Membrane vesicles prepared in the presence of adenosine diphosphate were loaded with K+ by incubation with 0.5 M potassium phosphate. Addition of valinomycin resulted in the synthesis of 0.2 to 0.3 nmol of ATP/mg of membrane protein, whereas no synthesis was observed after addition of nigericin. Addition of K+, dicyclohexylcarbodiimide, carbonylcyanide p-trifluoromethoxyphenylhydrazone, or azide to the assay buffer inhibited ATP synthesis. Adenosine diphosphate and Mg2+ were found to be required. Ca2+, which can replace Mg2+ for the hydrolytic activity of the Mg2+-adenosine triphosphatase (ATPase) (EC 3.6.1.3), could not replace Mg2+ in the synthetic reaction and, in fact, inhibited ATP synthesis even in the presence of Mg2+. Strain NR-70, a mutant lacking the Mg2+-ATPase, was unable to synthesize ATP using an artificially imposed membrane potential. Additionally, the Mg2+-ATPase was found to contain tightly bound ATP.

Adenosine Diphosphate↗
PubMed1978

In vitro action of bombesin on amylase secretion, membrane potential, and membrane resistance in rat and mouse pancreatic acinar cells. A comparison with other secretagogues.

Bombesin caused depolarization of rat or mouse pancreatic acinar cell membrane, reduction of membrane resistance, and a steep rise in amylase output from superfused pancreatic fragments. These effects were similar to those previously described for acetylcholine, cholecystokinin, and gastrin. The dose-response curves for these three effects of bombesin were very similar, with effects being detectable at concentrations of about 30 pM and maximal effects at about 10 nM. The equilibrium potential for the membrane action of bombesin, i.e., the membrane potential at which bombesin did not cause any change in membrane potential, was -16 mV. Similar values for equilibrium potential were obtained with acetylcholine, caerulein and pentagastrin. Bombesin in the higher dose range (10 nM) caused electrical uncoupling of acinar cells within an acinus, i.e., a marked increase in junctional membrane resistance. Similar uncoupling effects were observed after acetylcholine, caerulein, and pentagastrin stimulation. In conclusion, bombesin acts on the pancreatic acinar plasma membrane in exactly the same way as acetylcholine and cholecystokinin-pancreozymin. The electrical uncoupling caused by stimulation is evidence for an increase in cytosol free calcium ion concentration.

Acetylcholine↗
PubMed1990

Effect of OPC-8490 on the membrane potentials and membrane currents of single guinea-pig myocytes.

The direct actions of OPC-8490 on mammalian myocardium were examined by determination of the drug's effects on the action potentials of isolated guinea-pig single ventricular cells and on the underlying ionic currents. OPC-8490 (10(-6) to 10(-4) M) did not alter the resting membrane potential, but rather produced a dose-dependent prolongation of the duration of the action potential. The amplitude of the action-potential plateau was also increased by OPC-8490. Whole-cell voltage clamp experiments revealed that OPC-8490 blocks myocardial delayed outward K+ current (IK), which regulates repolarization of the action potentials. However Ik1, which regulates the resting membrane potential, was not changed by OPC-8490. Ca current (ICa) was increased by OPC-8490 in a dose-dependent and reversible manner. These results suggest that OPC-8490 augments the plateau amplitude and increases the duration of the action potentials by not only increasing ICa, but also by decreasing delayed outward K+ currents. Moreover, OPC-8490 did not affect the intracellular concentration of cyclic AMP in single cells. The OPC-8490 increase in ICa was thus unlikely to be mediated by a process involving cyclic AMP.

Action Potentials↗
PubMed1978

Thermal membrane potential across charged membranes in 2-1 and 1-2 electrolyte solutions.

Measurements of thermal membrane potential across cation exchange membranes in MgCl2, CaCl2 and BaCl2 solutions and across anion exchange membranes in K2SO4, Na2SO4 and K2CO3 solutions were carried out. The magnitude of the thermal membrane potential for divalent counterions is lower than that for monovalent counterions. If the transport number of counterions in the membrane phase is unity, the slopes of the temperature coefficient of thermal membrane potential against logarithmic activities of counterion in the external solution are predicted to be--R/2F for 2-1 electrolytes with cation exchange membranes and R/2F for 1-2 electrolytes with anion exchange membranes, respectively.

Electrolytes↗
PubMed1976

Thermal membrane potential across charged membranes in NaCl-NH4Cl and LiCl-NH4Cl solutions.

Measurements of the thermal membrane potential across cation exchange membranes were carried out by using aqueous solutions containing two 1-1 electrolytes, with an anion in common. The same solution was used on both sides of the membrane. In all cases a good linear relationship was observed between the thermal membrane potential delta psi and the temperature difference delta T (in the range delta T = +/- 10 degrees C). Assuming that the activity of one cation is equal to that of another cation in the solutions and the sum of transport numbers of cations is unity, the plot of delta psi/delta T vs logarithmic activity of one cation is linear with a slope of R/F. These experimental results are in agreement with a theory presented previously. From the analysis of thermal membrane potential in mixtures of electrolytes it is obtained that the cross coefficient of cation-cation interaction in membranes is negative and about 6 to 9% of the main coefficient.

Ammonium Chloride↗
PubMed1975

Thermal membrane potential through charged membranes in electrolyte solutions.

Measurements of the thermal membrane potential across cation and anion exchange membranes were carried out by using the same solution of various 1-1 electrolytes on both sides of the membrane. In all cases a good linear relationship was observed between the thermal membrane potential increment psi and the temperature difference increment T. The slope of the linear plot varied with the concentration of the electrolyte. The value of increment psi/increment T versus logarithmic activity of the electrolyte plot was linear with a slope of +/- R/F if the transport number of counterion was unity. The magnitude of increment psi/increment T was independent of coion species but dependent on counterions. These experimental results are in agreement with a theory presented previously. The thermal membrane potential caused by the direct effect of temperature differences and that by the indirect effect arising from the changes in ionic and water chemical potentials due to the temperature difference are separately discussed.

Cations, Monovalent↗
PubMed1991

Difluorophosphate as a 19F NMR probe of erythrocyte membrane potential.

Erythrocyte membrane potential can be estimated by measuring the transmembrane concentration (activity) distribution of a membrane-permeable ion. We present here the study of difluorophosphate (DFP) as a 19F NMR probe of membrane potential. This bicarbonate and phosphate analogue has a pKa of 3.7 +/- 0.2 (SD, n = 4) and therefore exists almost entirely as a monovalent anion at physiological pH. When it is incorporated into red cell suspensions, it gives two well resolved resonances that arise from the intra- and extracellular populations; the intracellular resonance is shifted approximately 130 Hz to higher frequency from that of the extracellular resonance. Hence the transmembrane distribution of DFP is readily assessed from a single 19F NMR spectrum and the membrane potential can be calculated using the Nernst equation. The membrane potential was independent of, DFP concentration in the range 4 to 59 mM, and haematocrit of the cell suspensions of 31.0 to 61.4%. The membrane potential determined by using DFP was 0.94 +/- 0.26 of that estimated from the transmembrane pH difference. The distribution ratios of intracellular/extracellular DFP were similar to those of the membrane potential probes, hypophosphite and trifluoroacetate. DFP was found to be transported across the membranes predominantly via the electrically-silent pathway mediated by capnophorin. Using magnetization transfer techniques, the membrane influx permeability-coefficient of cells suspended in physiological medium was determined to be 7.2 +/- 2.5 x 10(-6) cm s-1 (SD, n = 4).

Erythrocyte Membrane↗
PubMed1978

Developmental changes in rat adrenocortical cell membrane potential.

Resting membrane potentials of zona fasciculata-reticularis cells of the rat adrenal gland varied with age. The mean membrane potentials of newborn rat adrenal cells was -56.4 +/- 0.7 mV in the first week of life. The mean potential increased slightly to -61.9 +/- 0.8 mV in the second week and then decreased with age to a mean of -38.5 +/- 0.8 mV in 25--50 week old rats and of -25.9 +/- 1.9 mV in 100 week old rats. The changes in membrane potential may correlate with the indices of adrenocortical growth and activity.

Adrenal Cortex↗
PubMed1992

The fertilization potential and associated membrane potential oscillations during the resumption of meiosis in the egg of the ascidian Phallusia mammillata.

The fertilization potential in Phallusia mammillata consisted of an initial rapid depolarization. This initial sperm-triggered depolarization was followed by a phase of membrane depolarization which was of either long or short duration, depending on the eggs. When of long duration, the phase of membrane depolarization was divided into two periods: the first one began with a plateau (Em = +20.2 +/- 1.1 mV; duration = 1.7 +/- 0.14 min) which was followed by a series of membrane potential oscillations (n = 3.1 +/- 0.25) lasting 2.4 +/- 0.2 min. The second period also began as a plateau (Em = approximately 0 mV; duration = 3.40 +/- 0.20 min) which was followed by a series of oscillations (n = 11.5 +/- 0.5) lasting 11.8 +/- 0.6 min, followed by a membrane repolarization. The second series of oscillations often continued rising from the resting potential value. In the eggs displaying a short duration of membrane depolarization, the second period of depolarization was shortened (lasting only 3.5 +/- 0.5 min) since it lacked the second plateau. In addition it displayed a smaller number of oscillations (n = 4.7 +/- 0.6). As a consequence of this shortening, the membrane repolarized sooner. After repolarization, the membrane displayed several potential oscillations that started from the repolarization level. Regardless of the length of the depolarized plateau phases, the total number of membrane oscillations and the time period during which they occurred were constant. Eggs displaying a long depolarization phase had 15.9 +/- 0.6 oscillations in a 19.5 +/- 0.6 min interval, while eggs having a short depolarization phase had 16.0 +/- 0.8 oscillations in a 18.1 +/- 0.3 min interval. The time period during which the potential oscillations occurred corresponded remarkably well with the time of the meiotic divisions: the formation of the first polar body was detected about 80 sec after the end of the first series of oscillations; the second polar body was extruded about 85 sec after the last membrane oscillation occurred.

Animals↗
PubMed1979

Inhibition of the respiratory-linked membrane potential in E. coli membrane vesicles by octapeptin.

Octapeptin is a peptide antibiotic which affects bacterial membrane structure and selective membrane permeability for protons and potassium. The influence of octapeptin on the formation of a membrane potential generated across bacterial vesicles was monitored using the Rb+-valinomycin transport system. Octapeptin inhibited the respiratory-linked generation of membrane potentials formed in the presence of succinate or Asc/PMS. In addition, the antibiotic inhibited [3H]-leucine transport driven either by succinate or Asc/PMS. These studies support the proposal that the antimicrobial activity of octapeptin is due to inhibition of the formation of a membrane potential generated in the presence of appropriate respiratory substrates.

Anti-Bacterial Agents↗
PubMed1991

[Effects of isoflurane on membrane potentials, refractory periods and membrane ionic currents in rabbit single ventricular myocytes].

In order to analyze direct action of isoflurane on myocardium, we studied effects of isoflurane on membrane potentials and transmembrane ionic currents in single ventricular myocytes isolated enzymatically from rabbit hearts. Membrane potentials were recorded with a suction microelectrode technique, and an action potential was elicited by a brief intracellular stimulus. Isoflurane 3% depressed the action potential overshoot, plateau phase and duration without changing resting potential. Isoflurane decreased the refractory period of the action potential and prolonged the time-constant (tau) of the recovery process. In corresponding voltage clamp experiments, isoflurane significantly depressed the Ca2+ current (ICa), which generates the plateau phase. However, isoflurane had no effect on the transient outward current (I(t)), which triggers repolarization of the action potential. In rabbit ventricular cells, the time- and voltage-dependent outward K+ current (IK) was nearly absent. In conclusion, the depression of the action potential plateau by isoflurane is due to the decrease of ICa. Since isoflurane has no effect on It, the depression of the plateau phase by isoflurane may explain the shortening in the duration and the refractory period of the action potential.

Action Potentials↗
PubMed1992

Effect of membrane potential on band 3 conformation in the human erythrocyte membrane detected by triplet state quenching experiments.

The triplet lifetime and absorption anisotropy decay of eosin-labeled band 3 was measured in resealed erythrocyte ghosts. Membrane potentials were generated by the addition of valinomycin in the presence of a K+ gradient. Neither negative nor positive membrane potentials had any detectable effect on the rotational diffusion of band 3 nor on the eosin triplet lifetime. The membrane potential did, however, affect quenching of the eosin triplet state by I- and TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl). Quenching was enhanced by a negative membrane potential (negative inside) and reduced by a positive membrane potential. In addition, it was found that a negative membrane potential enhanced the efficiency of eosin labeling of band 3 in intact erythrocytes. A positive membrane potential had the opposite effect. These results indicate that the eosin binding site on band 3 becomes more accessible to the extracellular aqueous phase in the presence of a negative membrane potential and less accessible in the presence of a positive membrane potential. Quenching by I- and TEMPO of the triplet state of eosin-labeled band 3 was further investigated as a function of pH. Quenching by TEMPO and its dependence on membrane potential were relatively insensitive to pH. In contrast, the rate of quenching by I- showed a marked decrease over the range pH 5.5-9.5. Moreover, the effect of a negative membrane potential on I- quenching also varied with pH. These results are discussed on the supposition that the eosin probe is located in the anion access channel of band 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Anion Exchange Protein 1, Erythrocyte↗
PubMed1976

[The "anomalous" relationship between the concentration of potassium in the medium and the membrane potential of muscle fibers with a decreased intracellular potassium concentration. III. Change in the membrane potential during prolonged muscle incubation in saccharose-sulfate media containing 2.5 or 75 mM of potassium].

At the external potassium concentration 2.5 mM, The value Em--Ek diminishes, but at 75 mM it increases, although the potassium fluxes are nearly balanced and nosignificant changes in internal potassium occur. The contribution of other ions to the electrogenesis is examined. An attempt is made to describe the movement of these ions by the Goldman equations. The permeability coeficients should have been much higher than potassium coefficient, and besides it should be admitted that the coefficients and the internal activity of ions discussed may vary with time.

Animals↗
PubMed1991

Heterogeneity in the effects of membrane potentials on pantothenate and glucose uptakes by rabbit renal apical membranes.

1. Previous studies using renal brush-border membrane vesicles have established that both the pantothenate and the low Km (Michaelis-Menten constant), low Vmax (maximal rate) D-glucose systems have a stoichiometry of 2 Na+: 1 organic molecule. In this study, we compared the mechanisms by which the membrane potential energizes pantothenate and D-glucose uptakes by brush-border membrane vesicles isolated from the whole cortex of rabbit kidney. 2. In the absence of Na+, varying the membrane potential from +60 to -60 mV decreased pantothenate uptake, whereas D-glucose uptake was increased in a linear manner. These results suggested the existence of a conductive pathway for pantothenate in these membranes. They also suggested that the pantothenate free carrier is electroneutral, while the glucose free carrier is negatively charged. 3. In the presence of an inwardly directed Na+ gradient, varying the membrane potential from +60 to -60 mV increased Na(+)-dependent pantothenate influx linearly. In contrast, a shift from +60 to +40 mV in the membrane potential had no influence on Na(+)-dependent D-glucose influx, whereas influx was a linear function of the membrane potential from +40 to -60 mV, indicating that there is a threshold membrane potential required for membrane potential-dependent D-glucose movement to occur. 4. Kinetic studies revealed that the effect of membrane potential on pantothenate uptake is through changes in the Km, while Vmax was unchanged. On the other hand, the membrane potential exerted its effect on D-glucose transport solely on the Vmax. 5. Finally, binding studies revealed that membrane potential, both in the presence and absence of a Na+ gradient, elicited effects on phlorizin binding qualitatively similar to those observed for D-glucose transport. 6. Implications of these findings for tubular regulation of these electrogenic secondary active transport systems are discussed.

Animals↗