Direct inhibition of voltage-dependent Ca2+ fluxes by ethanol and higher alcohols in rabbit T-tubule membranes

The effects of ethanol and higher alcohols on Ca-45(2+) fluxes, mediated by voltage-dependent Ca2+ channels (VDCCs), were investigated in inside-out t ransverse (T)-tubule membrane vesicles from rabbit skeletal muscle. Ca-45(2 +) effluxes were induced by membrane potentials generated via establishing K+ gradients across the vesicles, and were significantly inhibited by the i norganic Ca2+ channel blocker La3+ (1 mM) and the Ca2+ channel antagonist n ifedipine (1-10 muM), Ethanol, in the concentration range of 100-400 mM, ca used a significant suppression of depolarization-induced Ca-45(2+) fluxes. Ethanol also functionally modulated the effect of nifedipine (1-10 muM) and the Ca2+ channel agonist Bay K 8644 (1 muM) on Ca2+ effluxes. Pretreatment with pertussis toxin (5 mug/ml) or phorbol 12-myrstate 13-acetate (PMA, 50 nM) did not affect the ethanol inhibition of Ca-45(2+) fluxes. Further exp eriments with alcohols revealed that butanol, hexanol, octanol and decanol also significantly inhibited Ca-45(2+) effluxes. However, undecanol and dod ecanol did not cause any significant change on Ca-45(2+) fluxes, indicating that the effects of alcohols on Ca-45(2+) effluxes exhibit a cut-off pheno menon. In radioligand binding studies, it was found that at the concentrati ons used in flux studies, alcohols did not alter the characteristics of the specific binding of [H-3]PN 200-110 to T-tubule membranes. Results indicat e that ethanol directly inhibits the function of voltage-dependent Ca2+ cha nnels without modulating the specific binding of Ca2+ channel ligands of th e dihydropyridine class, and that this inhibition is independent of intrace llular Ca2+ levels. (C) 2001 Published by Elsevier Science B.V.