Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Valinomycin”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 505 records · Page 28Linked to original sources
PubMed2001

Role of quinine-sensitive ion channels in volume regulation in boar and bull spermatozoa.

The ability to reverse swelling caused by hypo-osmotic stress is an important cell function; in spermatozoa, it is likely to be of consequence during ejaculation and also during the thawing process that terminates cryopreservation. In this study, the time course of boar and bull sperm volume changes after exposure to hypo-osmotic conditions at 39 degrees C was recorded. Cell volume measurements of washed sperm suspensions were performed electronically in Hepes-buffered saline solutions of 300 and 180 mosmol kg(-1) containing 2.5 mmol K(+) l(-1). Treatment with quinine in the presence or absence of the potassium ionophore valinomycin was used to determine whether potassium channels were involved in the reversal of swelling. After exposure to hypo-osmotic conditions, both bull and boar spermatozoa showed initial swelling (up to 200% and 140% of initial volume, respectively, within 5 min), which was subsequently partially reversed (to about 150% and 120%, respectively, after 20 min). Incubation with quinine led to an increase in swelling in both species. However, bull sperm volume was already maximal (up to 294%) after 30 s and declined thereafter, whereas boar sperm volume increased slowly to a maximum of about 220% after 20 min. Valinomycin treatment caused quinine-induced swelling in bull spermatozoa to decrease rapidly to control (no quinine, no valinomycin) values, whereas in quinine-treated boar spermatozoa it had an opposite, enhancing effect. Interpreting these results in the light of data from studies by others on a variety of cell types, it is proposed that swelling-activated potassium channels are involved in regulatory volume decrease in both species of spermatozoa, but that boar spermatozoa may contain fewer swelling-activated chloride channels than do bull spermatozoa.

Animals↗
PubMed1993

Regulation of Cl- conductance in delayed shortening and shrinkage of outer hair cells.

Tetanic electrical field stimulation induces slow and delayed shortening of isolated outer hair cells (OHCs) from guinea pigs concomitant with a decrease in cell volume and intracellular Cl- concentration ([Cl-]i). These responses are dependent on the entry of Ca2+ and the activation of both Ca(2+)-activated K+ channels and furosemide-sensitive Cl- channels. In this study, the regulatory mechanisms of the Cl- channels of OHCs were investigated. Tetanic stimulation induced shrinkage and a decrease in [Cl-]i, the latter being unrelated to the activity of the Na+/K+/2Cl- cotransporter. These responses were inhibited by tetraethylammonium, and the inhibition was overcome by an increase in the K+ conductance by valinomycin, though valinomycin alone did not affect the resting cell volume and [Cl-]i. The deprivation of extracellular Ca2+ inhibited the stimulation-induced changes in volume and [Cl-]i even in the presence of valinomycin. These results suggest that electrical stimulation-induced delayed shortening and shrinkage of OHCs are induced by Cl- efflux, which is electrically coupled to K+ efflux and independently activated following an increase in intracellular Ca2+ concentration.

Animals↗
PubMed1978

Histone inhibition of mitochondrial proton transport.

Histone blocks proton uptake by mitochondria incubated in the presence of valinomycin or DNP. In the presence of DNP valinomycin-induced H+ uptake is not affected by histone. H+ uptake induced by nigericin is not affected by histone as well. Postulated mechanism of histone action involves the immobilization of proton translocation in mitochondrial membrane and induction of local change in H+ concentration, the prevention of the interaction between H+ and natural K+-carrier and Mg2+ transport system or valinomycin.

Animals↗
PubMed1997

Effect of nigericin, monensin, and tetronasin on biohydrogenation in continuous flow-through ruminal fermenters.

Four ionophores differing in cation selectivity were compared for their effect on microbial fermentation and biohydrogenation by ruminal bacteria in continuous culture. Monensin and nigericin are monovalent antiporters with selective binding affinities for Na+ and K+, respectively. Tetronasin is a divalent antiporter that binds preferentially with Ca2+ or Mg2+. Valinomycin is a monovalent uniporter and does not exchange K+ for H+. Steady-state concentrations of 2 micrograms/ml of monensin, nigericin, tetronasin, or valinomycin were maintained by constant infusion into fermenters. Molar percentages of acetate were lower, and those of propionate were higher, in the presence of monensin, nigericin, and tetronasin; all three ionophores also decreased CH4 production. Concentrations of valinomycin as high as 8 micrograms/ml had no effect on volatile fatty acids or CH4 production. Monensin, nigericin, and tetronasin inhibited the rate of biohydrogenation of linoleic acid. Continuous infusion of C18:2n-6 at a steady-state concentration of 314 micrograms/ml into fermenters receiving monensin, nigericin, or tetronasin resulted in lower amounts of stearic acid and higher amounts of oleic acid. Ionophores increased total C18:2 conjugated acids mainly because of an increase in the cis-9, trans-11-C18:2 isomer. If reflected in milk fat, ionophore-induced changes in ruminal lipids could enhance the nutritional qualities of milk.

Animals↗
PubMed2001

Dissipation of potassium and proton gradients inhibits mitochondrial hyperpolarization and cytochrome c release during neural apoptosis.

Exposure of rat hippocampal neurons or human D283 medulloblastoma cells to the apoptosis-inducing kinase inhibitor staurosporine induced rapid cytochrome c release from mitochondria and activation of the executioner caspase-3. Measurements of cellular tetramethylrhodamine ethyl ester fluorescence and subsequent simulation of fluorescence changes based on Nernst calculations of fluorescence in the extracellular, cytoplasmic, and mitochondrial compartments revealed that the release of cytochrome c was preceded by mitochondrial hyperpolarization. Overexpression of the anti-apoptotic protein Bcl-xL, but not pharmacological blockade of outward potassium currents, inhibited staurosporine-induced hyperpolarization and apoptosis. Dissipation of mitochondrial potassium and proton gradients by valinomycin or carbonyl cyanide p-trifluoromethoxy-phenylhydrazone also potently inhibited staurosporine-induced hyperpolarization, cytochrome c release, and caspase activation. This effect was not attributable to changes in cellular ATP levels. Prolonged exposure to valinomycin induced significant matrix swelling, and per se also caused release of cytochrome c from mitochondria. In contrast to staurosporine, however, valinomycin-induced cytochrome c release and cell death were not associated with caspase-3 activation and insensitive to Bcl-xL overexpression. Our data suggest two distinct mechanisms for mitochondrial cytochrome c release: (1) active cytochrome c release associated with early mitochondrial hyperpolarization, leading to neuronal apoptosis, and (2) passive cytochrome c release secondary to mitochondrial depolarization and matrix swelling.

Animals↗
PubMed1992

Mitochondrial DNA is not fragmented during apoptosis.

We have exposed mouse thymocytes and P-815 mastocytoma cells to four different conditions reported to cause apoptosis: 1) incubation in the absence of mitogenic factors; 2) incubation in the presence of dexamethasone; 3) stimulation with external ATP; 4) treatment with high concentrations of the K+ ionophore valinomycin. These treatments caused DNA fragmentation to a varying extent in the two cell types. High stringency hybridization with a cDNA probe specific to a mitochondrial DNA sequence revealed that during apoptosis induced by lack of mitogenic factors, dexamethasone, or extracellular ATP, mitochondrial DNA was not fragmented. On the contrary, valinomycin caused extensive degradation of mitochondrial DNA. These results support the notion that DNA fragmentation during apoptosis is a specific nuclear event and suggest that other agents, such as valinomycin, may act less selectively.

Adenosine Triphosphate↗
PubMed1991

Mechanisms of ionophore-induced stimulation of renin secretion with special reference to a chemiosmotic hypothesis.

The effects of several ionophores on renin secretion were investigated in rabbit renal cortical slices. When slices were incubated in the absence of Ca++, the K+ ionophore valinomycin (10(-5) approximately 5 x 10(-4) M) or the monovalent cation ionophore nonactin (10(-4) M) stimulated renin secretion about 2-fold. The renin secretion stimulated by valinomycin was further increased by inclusion of the H+ ionophore, carbonylcyanide m-chlorophenylhydrazone. The electroneutral K+/H+ exchange ionophore nigericin (10(-5) approximately 5 x 10(-4) M) stimulated renin secretion in a dose-dependent manner, producing a maximal stimulation of about 17-fold. Another electroneutral exchange ionophore, monensin, also significantly stimulated secretion. The stimulation by both valinomycin and nigericin was apparent whether slices were incubated in Na(+)-rich or K(+)-rich media. The extent of stimulation by the two ionophores was dependent upon the presence of anion with acetate greater than Cl greater than isethionate greater than thiocyanate. Thiocyanate itself markedly inhibited renin secretion. Incubating of slices in an iso-osmotic ammonium acetate medium which is known to induce rapid swelling of secretory granules, stimulated renin secretion to the magnitude comparable to that of maximal stimulation by nigericin in a potassium acetate medium. The pattern of response to these ionophores indicates that changes in K+, H+ and anion gradients across the renin secretory granule may modulate renin secretory rate. It is proposed that conditions which allow accumulation of K+ and anion within acidic renin secretory granules lead to osmotic swelling of the granules and that granule swelling may promote exocytosis.

Animals↗
PubMed1987

Plasma membrane potential modulates chemotactic peptide-stimulated cytosolic free Ca2+ changes in human neutrophils.

The relationship between fMet-Leu-Phe-induced changes in the cytosolic free Ca2+ concentration [( Ca2+]i), plasma membrane potential depolarization, and metabolic responses was studied in human neutrophils. Receptor-activated depolarization occurred both at high and resting [Ca2+]i, but was inhibited at very low [Ca2+]i. Phorbol 12-myristate 13-acetate-induced plasma membrane depolarization, on the contrary, was independent of [Ca2+]i. The threshold fMet-Leu-Phe concentration for plasma membrane depolarization (10(-8) M) was at least 1 log unit higher than that for [Ca2+]i increases (5 X 10(-10) M) and coincident with that for NADPH oxidase activation. Nearly maximal [Ca2+]i increases were elicited by 3 X 10(-9) fMet-Leu-Phe in the absence of any significant plasma membrane potential change. This observation allowed us to investigate the effects of artificially induced plasma membrane depolarization and hyperpolarization at low fMet-Leu-Phe concentrations (10(-9) to 3 X 10(-9) M) which did not perturb plasma membrane potential. Depolarizing (gramicidin D at 10(-7) to 10(-6) M or KCl at 50 mM) and hyperpolarizing (valinomycin at 4 microM) treatments had little influence on unstimulated [Ca2+]i levels, whereas fMet-Leu-Phe-induced transients were significantly altered. Gramicidin D and KCl decreased the fMet-Leu-Phe-induced [Ca2+]i increases in Ca2+-containing or in Ca2+-free media. Valinomycin, on the contrary, increased receptor-stimulated [Ca2+]i increases, and the effect was larger in the presence of extracellular Ca2+. Valinomycin also strongly potentiated secretion. It is suggested that plasma membrane depolarization in human neutrophils is a physiological feedback mechanism inhibiting receptor-dependent [Ca2+]i changes.

Calcium↗
PubMed1988

[ATP synthesis in Staphylococcus aureus cells during induction of membrane potentials and proton gradient].

The dynamics of ATP synthesis in Staphylococcus aureus cells was studied during membrane potential induction and K+ gradient generation in the presence of valinomycin. The starting level of intracellular ATP was 0.05 mM. Valinomycin (30 micrograms/ml) caused an increment of the intracellular ATP level up to 0.25 mM. The protonophore uncoupler, m-chlorinecarbonylcyanidephenylhydrazonium, and the H+-ATPase inhibitor, N,N'-dicyclohexylcarbodiimide, effectively suppress ATP synthesis induced by valinomycin. No ATP synthesis occurs at K+ concentration of 200 mM. The transmembrane gradient formation results in the synthesis of a smaller amount of ATP (0.10 mM).

Adenosine Triphosphate↗
PubMedDate not supplied

[A study of passive Ca2+ flow through the sarcoplasmic reticulum of skeletal muscles. II. Stimulation of passive Ca2+ influx with monovalent cations and anions].

The initial rate of passive Ca2+ influx into "heavy" and "light" fractions of sarcoplasmic reticulum (SR) vesicles increases in the presence of univalent cation chlorides. Stimulation of passive Ca2+ influx decreases in the following order: KCl + valinomycin-KSCN- + valinomycin greater than KSI = NaCl greater than choline chloride. K-gluconate + valinomycin and K-gluconate have no effect on the passive Ca2+ influx into SR vesicles. It is supposed that KCl-stimulation of passive Ca2+ influx into SR vesicles under conditions used may be caused by depolarization of the SR membrane.

Animals↗
PubMed1975

Postillumination adenosine triphosphate synthesis in Rhodospirillum rubrum chromatophores. II. Stimulation by a K+ diffusion potential.

Addition of valinomycin, nonactin, or monactin plus KCl in the dark to preilluminated chromatophores induced the synthesis of a large amount of ATP. This stimulation of postillumination ATP synthesis by a dark-imposed K+ diffusion potential was different from the stimulation caused by addition of permeant anions or cations in the light, since it increases when the pH of the light stage decreased from 8.0 to 6.0. It was thus most pronounced when the chromatophores were preloaded with protons but the light-induced proton concentration gradient (deltapH) was low. Imposition of a Kplus diffusion potential resulted however in stimulation of ATP synthesis even when the light-induced deltapH was already above the threshold value required to initiate postillumination ATP synthesis. This situation was realized when valinomycin plus KCl were added in the dark to chromatophores preilluminated above pH 6.7 with thiocyanate as the permeant anion, and the amount of ATP formed was the sum of the yields obtained with each of these affectors by itself. On the other hand addition of thiocyanate together with valinomycin plus KCl in the dark led to inhibition of ATP synthesis. In this case the permeant anion could not affect the light-induced deltapH but it did eliminate the diffusion potential by decreasing the difference between the permeabilities of Kplus and the anion present in the reaction mixture.

Adenosine Triphosphate↗
PubMed1982

[Comparison of the effects of some perminductors on mitochondria and chloroplasts].

The effects of valinomycin, gramicidins A and S, melittin and the protonophore 3,5-di-tert-butyl-4-hydroxybenzylidenmalononitrile on rat liver mitochondria and pea chloroplasts during active electron transport were studied. The canalogenes melittin and gramicidin S as well as gramicidin A and the protonophore increase the proton conductance of the inner mitochondrial membrane and chloroplast tylakoid membrane. The curve for the dependence of the canalogene effects on their concentration is S-shaped for both types of the organelles. Valinomycin reveals no protonophore activity and at high concentrations inhibits electron transport in both types of the coupling membranes. The uncoupling activity of gramicidin A and canalogenes and the inhibiting activity of valinomycin do not depend on the type of organelles when the concentration of these compounds is expressed as concentration in the membrane lipid matrix. At the same time the activity of the protonophore in chloroplasts is 6 times less than that in mitochondria. It is assumed that this difference in the protonophore activity is due to the differences in the mechanism of coupling of electron transport rather than to the peculiarities of lipid composition of mitochondria and chloroplasts. The lack of dependence of activity of peptide perminductors on the membrane lipid composition can probably be due to the fact that their effects is localized in the carbohydrate moiety of the lipid bilayer and does not involve the polar "heads" of the lipids.

Animals↗
PubMed1993

Changes in the membrane potential can affect pepsinogen secretion of isolated rat chief cells.

The aim of this study was to determine pepsinogen secretion by isolated rat chief cells in relation to changes of membrane potential obtained by the use of potassium ionophore valinomycin and different extracellular K+ concentrations, or protonophore carbonyl cyanide m-chlorophenyl hydrazone (CCCP) at different pH. While valinomycin or CCCP decreased basal and cAMP-stimulated secretory response of the chief cells, they increased secretion of pepsinogen stimulated by calcium ionophore A23187. When Ca2+ was absent from the incubation media, A23187-stimulated secretion of pepsinogen significantly decreased. Moreover, the omission extracellular calcium reversed the potentiating effects of valinomycin or CCCP on A23187-stimulated secretory response. It is known that pepsinogen secretion is a biphasic process. In the first phase, Ca2+ is released from its intracellular stores, while the second one depends on extracellular calcium entering the cell. Our results suggest that this phase is dependent also on membrane potential.

Animals↗
PubMed1976

[Comparison of the electrical and isotope characteristics of ionic transport through bilateral phospholipid membranes].

Simultaneous measurements of electrochemical characteristics and tracer fluxes have been made using large spherical bilayer lipid membranes (1-2 cm2 area). The results obtained show the predominant contribution of electrically silent chloride molecules to the fluxes through unmodified membranes. In cases of valinomycin modified (valinomycin concentration=10(-7)M) membranes (in 0.1 M solutions of KCl, RbCl and CsCl) the fluxes are determined exclusively by cations. The membrane permeability for 22Na, in 0.1 NaCl solution, does not depend on the valinomycin concentration. The selectivity sequences obtained by electrochemical and tracer methods are compared and discussed.

Cesium↗
PubMed1999

Membrane hyperpolarization by sperm-activating and -attracting factor increases cAMP level and activates sperm motility in the ascidian Ciona intestinalis.

In the ascidian Ciona intestinalis (and C. savignyi), sperm-activating and -attracting factor (SAAF) is released from the egg at fertilization and stimulates both Ca(2+) influx and a transient increase in cAMP level of the sperm, leading to the activation of sperm motility (M. Yoshida et al., 1994, Dev. Growth Differ. 36, 589-595). In this paper we show in C. intestinalis that valinomycin, a potassium-selective ionophore, as well as SAAF, activated sperm motility, and this activation was suppressed by extracellular high K(+). Membrane potential measurements showed that both SAAF and valinomycin increase K(+) permeability of sperm and induce membrane hyperpolarization, the amplitude of which depends on the external K(+) concentration. The membrane potential and intracellular K(+) concentration of Ciona sperm without SAAF were estimated to be about -50 mV and 560 +/- 40 mM, respectively. After treatment with SAAF or valinomycin the membrane potential became almost equal to the equilibrium potential of K(+) (-100 mV), and the cAMP level increased in artificial seawater. A potent voltage-dependent K(+) channel blocker, MCD peptide, at the concentration of 10 microM blocked SAAF-induced hyperpolarization of the cells, increase in cAMP, and sperm motility. These results suggest that membrane hyperpolarization produced by the opening of K(+) channels elevates cAMP synthesis and leads to the activation of sperm motility in Ciona.

Animals↗
PubMed1992

Amiloride sensitivity of proton-conductive pathways in gastric and intestinal apical membrane vesicles.

Passive proton permeability of gastrointestinal apical membrane vesicles was determined. The nature of the pathways for proton permeation was investigated using amiloride. The rate of proton permeation (kH+) was determined by addition of vesicles (pHi = 6.5) to a pH 8.0 solution containing acridine orange. The rate of recovery of acridine orange fluorescence after quenching by the acidic vesicles ranged from 4 x 10(-3) (gastric parietal cell stimulation-associated vesicles; SAV) and 5 x 10(-3) (duodenal brush-border membrane vesicles; dBBMV) to 11 x 10(-3) sec-1 (ileal BBMV; iBBMV). Amiloride, 0.03 and 0.1 mM, significantly reduced the rate of proton permeation in dBBMV and iBBMV, but not gastric SAV. The decreases in kH+ were proportionately greater in iBBMV as compared with dBBMV. The presence of Na+/H+ exchange was demonstrated in both dBBMV and iBBMV by proton-driven (pHi less than pHo) 22Na+ uptake. Evidence was also sought for the conductive nature of pathways for proton permeation. Intravesicular acidification, again determined by quenching of acridine orange fluorescence, was observed during imposition of K(+)-diffusion potential ([K+]i much much greater than [K+]o). In dBBMV and iBBMV, intravesicular acidification was enhanced in the presence of the K(+)-ionophore valinomycin, indicating that the native K+ permeability is rate limiting. In the presence of valinomycin, the K(+)-diffusion potential drove BBMV intravesicular acidification to levels close to the electrochemical potential. In gastric SAV, acidification was not limited by the K+ permeability. Valinomycin was without effect, but the K+/H+ ionophore nigericin enhanced acidification in gastric SAV, illustrating the low proton permeability of these membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗
PubMed2002

Opening of ATP-sensitive potassium channels causes generation of free radicals in vascular smooth muscle cells.

Recent evidence suggests that opening of mitochondrial K(ATP) channels in cardiac muscle triggers the preconditioning phenomenon through free radical production. The present study tested the effects of K(ATP) channel openers in a vascular smooth muscle cell model using the fluorescent probe MitoTracker (MTR) Red trade mark for detection of reactive oxygen species (ROS). Rat aortic smooth muscle cells (A7r5) were incubated with 1 micro M reduced MTR (non-fluorescent) and the MTR oxidation product (fluorescent) was quantified. Thirty-minute pretreatment with either diazoxide (200 micro M) or pinacidil (100 micro M), both potent mitochondrial K(ATP) channel openers, increased fluorescent intensity (FI) to 149 and 162 % of control (p < 0.05 for both), respectively, and the K(ATP) channel inhibitor 5-hydroxydecanoate (5 HD) blocked it. Valinomycin, a potassium-selective ionophore, raised FI to 156 % of control (p <: 0.05). However, 5 HD did not affect the valinomycin-induced increase in FI. Inhibition of mitochondrial electron transport (myxothiazol) or uncoupling of oxidative phosphorylation (dinitrophenol) also blocked either valinomycin- or diazoxide-induced increase in FI, and free radical scavengers prevented any diazoxide-mediated increase in fluorescence. Finally the diazoxide-induced increase in fluorescence was not blocked by the PKC inhibitor chelerythrine, but was by HMR 1883, a putative surface K(ATP) channel blocker. Thus opening of K(ATP) channels increases generation of ROS via the mitochondrial electron transport chain in vascular smooth muscle cells. Furthermore, a potassium-selective ionophore can mimic the effect of putative mitochondrial KATP channel openers. We conclude that potassium movement through KATP directly leads to ROS production by the mitochondria.

ATP-Binding Cassette Transporters↗
PubMed1978

A study of H+ transport in gastric microsomal vesicles using fluorescent probes.

Fluorescent amines, 9-aminoacridine, acridine orange and quinacrine, were used as probes for a pH gradient (deltapH) across gastric microsomal vesicles. Analysis of probe uptake data indicates that 9-aminoacridine distributes across the membrane as a weak base in accordance with the deltapH. On the other hand, acridine orange and quinacrine show characteristics of binding to membrane sites in addition to the accumulation in response to deltapH. A discussion of the advantages and limitations of the probes is presented. Application of these probes to pig gastric microsomal vesicles indicates that that K+-stimulated ATPase is responsible for the transport of H+ into the vesicles and thus develops a deltapH across the membrane. The deltapH generated by the K+-ATPase has a definite requirement for internal K+. The proton gradient can be discharged slowly after ATP depletion or rapidly either by detergent disruption of the vesicles or by increasing their leakiness using both H+ and K+ ionophores. On the other hand, the sole use of the K+ ionophore, valinomycin, stimulates the ATP-induced formation of deltapH by increasing the availability of K+ to internal sites. This stimulation by valinomycin requires the presence of permeable anions like Cl-. Analysis of the Cl- requirement indicates that in the presence of valinomycin the net effect is the accumulation of HCl inside the gastric vesicles. With an external pH of 7.0, the ATP-generated deltapH was calculated to be from 4 to 4.5 pH units. The results are consistent with the hypothesis that the K+-stimulated ATPase drives a K+/H+ exchange across the gastric vesicles. Since other lines of evidence suggest that these gastric microsomes are derived from the tubulovesicular system of the oxyntic cell, the participation of the ATP-driven transport processes in gastric HCl secretion is of interest.

Acridines↗