Direct inhibition of voltage-dependent Ca(2+) fluxes by ethanol and higher alcohols in rabbit T-tubule membranes.
The effects of ethanol and higher alcohols on 45Ca(2+) fluxes, mediated by voltage-dependent Ca(2+) channels (VDCCs), were investigated in inside-out transverse (T)-tubule membrane vesicles from rabbit skeletal muscle. 45Ca(2+) effluxes were induced by membrane potentials generated via establishing K(+) gradients across the vesicles, and were significantly inhibited by the inorganic Ca(2+) channel blocker La(3+) (1 mM) and the Ca(2+) channel antagonist nifedipine (1-10 microM). Ethanol, in the concentration range of 100-400 mM, caused a significant suppression of depolarization-induced 45Ca(2+) fluxes. Ethanol also functionally modulated the effect of nifedipine (1-10 microM) and the Ca(2+) channel agonist Bay K 8644 (1 microM) on Ca(2+) effluxes. Pretreatment with pertussis toxin (5 microg/ml) or phorbol 12-myrstate 13-acetate (PMA, 50 nM) did not affect the ethanol inhibition of 45Ca(2+) fluxes. Further experiments with alcohols revealed that butanol, hexanol, octanol and decanol also significantly inhibited 45Ca(2+) effluxes. However, undecanol and dodecanol did not cause any significant change on 45Ca(2+) fluxes, indicating that the effects of alcohols on 45Ca(2+) effluxes exhibit a cut-off phenomenon. In radioligand binding studies, it was found that at the concentrations used in flux studies, alcohols did not alter the characteristics of the specific binding of [3H]PN 200-110 to T-tubule membranes. Results indicate that ethanol directly inhibits the function of voltage-dependent Ca(2+) channels without modulating the specific binding of Ca(2+) channel ligands of the dihydropyridine class, and that this inhibition is independent of intracellular Ca(2+) levels.
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Loeb Research Institute, Neuroscience, 725 Parkdale Ave., K1Y 4K9, Ottawa, ON, Canada. moz@intra.nida.nih.gov
Tchugunova
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YB
Dunn
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D000438:Alcohols / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D000440:Butanols / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002132:Calcium Radioisotopes; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D000431:Ethanol / Q000494:pharmacology*; D000441:Hexanols / Q000494:pharmacology; D017275:Isradipine / Q000378:metabolism; D007811:Lanthanum / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D000442:Octanols / Q000494:pharmacology; D011817:Rabbits; D013329:Structure-Activity Relationship
D000438:Alcohols; D000440:Butanols; D002121:Calcium Channel Blockers; D002132:Calcium Radioisotopes; D000441:Hexanols; D000442:Octanols; D000431:Ethanol; D007811:Lanthanum; D009543:Nifedipine; D002118:Calcium; D017275:Isradipine