Actin cytoskeletal modulation of pressure-induced depolarization and Ca(2+) influx in cerebral arteries.
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The objective of this study was to examine the role of the actin cytoskeleton in the development of pressure-induced membrane depolarization and Ca(2+) influx underlying myogenic constriction in cerebral arteries. Elevating intraluminal pressure from 10 to 60 mmHg induced membrane depolarization, increased intracellular cytosolic Ca(2+) concentration ([Ca(2+)](i)) and elicited myogenic constriction in both intact and denuded rat posterior cerebral arteries. Pretreatment with cytochalasin D (5 microM) or latrunculin A (3 microM) abolished constriction but enhanced the [Ca(2+)](i) response; similarly, acute application of cytochalasin D to vessels with tone, or in the presence of 60 mM K(+), elicited relaxation accompanied by an increase in [Ca(2+)](i). The effects of cytochalasin D were inhibited by nifedipine (3 microM), demonstrating that actin cytoskeletal disruption augments Ca(2+) influx through voltage-sensitive L-type Ca(2+) channels. Finally, pressure-induced depolarization was enhanced in the presence of cytochalasin D, further substantiating a role for the actin cytoskeleton in the modulation of ion channel function. Together, these results implicate vascular smooth muscle actin cytoskeletal dynamics in the control of cerebral artery diameter through their influence on membrane potential as well as via a direct effect on L-type Ca(2+) channels. (+info)
Antibiotic A-130, isolation and characterization.
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An antibiotic, A-130, was isolated from a strain identified as Streptomyces hygroscopicus, strain A-130. The antibiotic belongs to the nigericin group and like dianemycin, has an alpha, beta-unsaturated ketone chromophore in its molecule. A-130 is active against gram-positive organisms. (+info)
The reversibility of active sulphate transport in membrane vesicles of Paracoccus denitrificans.
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An uncoupler-sensitive active transport of sulphate into membrane vesicles prepared from the plasma membrane of Paracoccus denitrificans (previously Micrococcus denitrificans) can be driven by respiration or by a trans-membrane pH gradient (alkaline inside) generated by the addition either of KCL ( in the presence of nigericin) or of NH4CL. Valinomycin does not substitute for nigericin. Respiration-driven transport is observed in right-side-out vesicles but not in inside-out vesicles, whereas transport driven by the addition of KCL (in the presence of nigericin) or of NH4CL is observed in both types of membrane vesicle. The active transport of sulphate into these vesicles is shown to be carrier-mediated by its sensitivity to thiol-group reagents. It is proposed that the sulphate carrier in the plasma membrane of P. denitrificans operates by a mechanism of electroneutral proton symport, and is capable of actively transporting sulphate in either direction across the plasma membrane, but that in whole cells respiration-driven proton expulsion drives the accumulative uptake of sulphate. (+info)
Vesicle transmembrane potential is required for translocation to the cytosol of externally added FGF-1.
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Externally added fibroblast growth factor-1 (FGF-1) is capable of crossing cellular membranes to reach the cytosol and the nucleus in a number of cell types. We have monitored the translocation of the growth factor by two methods: phosphorylation of FGF-1, and prenylation of an FGF-1 mutant that contains a C-terminal prenylation signal. Inhibition of endosomal acidification by ammonium chloride or monensin did not block the translocation of FGF-1, whereas bafilomycin A1, a specific inhibitor of vacuolar proton pumps, blocked translocation completely. A combination of ionophores expected to dissipate the vesicular membrane potential (valinomycin plus monensin) also fully inhibited the translocation. The inhibition of translocation by bafilomycin A1 was overcome in the presence of monensin or nigericin, while ouabain blocked translocation under these conditions. The data indicate that translocation of FGF-1 to cytosol occurs from the lumen of intracellular vesicles possessing vacuolar proton pumps, and that a vesicular membrane potential is required. Apparently, activation of vesicular Na+/K+-ATPase by monensin or nigericin generates a membrane potential that can support translocation when the proton pump is blocked. (+info)
Studies on the mode of action of reutericyclin.
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The mode of action of reutericyclin was determined with fluorescent dyes that probed the permeability of the cytoplasmic membrane by large molecules, protons, and potassium. A comparison of reutericyclin activity with those of nisin, nigericin, and valinomycin demonstrated that reutericyclin does not form pores but selectively dissipates the transmembrane proton potential. (+info)
Thylakoid targeting of Tat passenger proteins shows no delta pH dependence in vivo.
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The Tat pathway is a major route for protein export in prokaryotes and for protein targeting to thylakoids in chloroplasts. Based on in vitro studies, protein translocation through this pathway is thought to be strictly dependent on a transmembrane delta pH. In this paper, we assess the delta pH sensitivity of the Tat pathway in vivo. Using Chlamydomonas reinhardtii, we observed changes in the efficiency of thylakoid targeting in vivo by mutating the Tat signal of the Rieske protein. We then employed two endogenous pH probes located on the lumen side of the thylakoid membranes to estimate spectroscopically the delta pH in vivo. Using experimental conditions in which the trans-thylakoid delta pH was almost zero, we found no evidence for a delta pH dependence of the Tat pathway in vivo. We confirmed this observation in higher plants using attached barley leaves. We conclude that the Tat pathway does not require a delta pH under physiological conditions, but becomes delta pH sensitive when probed in vitro/in organello because of the loss of some critical intracellular factors. (+info)
In general, enveloped viruses use two different entry strategies and are classified accordingly into pH-dependent and pH-independent viruses. Different members of the retrovirus family use one or the other strategy. Little is known about the uptake of foamy viruses (FV), a special group of retroviruses, into the target cells. In this study, we examined the pH dependence of FV entry by analyzing FV envelope glycoprotein (Env)-mediated infection of target cells with murine leukemia virus or FV vector pseudotypes in the presence of various lysosomotropic agents. Similar to vesicular stomatitis virus glycoprotein G (VSV-G)-mediated uptake, FV Env-mediated entry was inhibited by various lysosomotropic agents, suggesting a pH-dependent endocytic pathway. However, in contrast to its effect on VSV-G pseudotypes, chloroquine failed to reduce the infectivity of FV Env pseudotypes, implying that the pathway is different from that of VSV-G. Glycoproteins of various other FV species showed inhibition profiles similar to that of the prototype FV (PFV) Env. Analysis of the pH dependence of the FV Env-mediated fusion process in a cell-to-cell fusion assay revealed an induction of syncytium formation by a short exposure to acidic pH, peaking around pH 5.5. Interestingly, of all FV Env species analyzed, only the PFV Env had a significant fusion activity at neutral pH. Taken together, these data suggest a pH-dependent endocytic pathway for infection of target cells by FV. (+info)
EPR study of light-induced regulation of photosynthetic electron transport in Synechocystis sp. strain PCC 6803.
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The kinetics of the light-induced redox changes of the photosystem 1 (PS 1) primary donor P(700) in whole cells of the cyanobacteria Synechocystis sp. PCC 6803 were studied by the electron paramagnetic resonance method. It was shown that the linear photosynthetic electron transport in cyanobacteria was controlled by two main mechanisms: (i) oxygen-dependent acceleration of electron transfer from PS 1 to NADP(+) due to activation of the Calvin cycle reactions and (ii) retardation of electron flow between two photosystems governed by a transmembrane proton gradient. In addition to the linear photosynthetic electron transport, cyanobacteria were capable of maintaining alternative pathways involving cyclic electron transfer around PS 1 and respiratory chains. (+info)