Calcium currents and peptide release from neurohypophysial terminals are inhibited by ethanol

The effects of EtOH on peptide release and on high-threshold, voltage-activated calcium (Ca++) channels were examined in acutely dissociated rat neurohypophysial terminals. These terminals release the peptide hormones, arginine vasopressin (AVP) and oxytocin. Release of AVP from isolated intact neurohypophyses, induced by either electrical stimulation or elevated potassium, was inhibited by clinically relevant concentrations of EtOH. "Whole-cell" patch-clamp recording methods were used to study the effects of EtOH on voltage-activated Ca++ currents (ICa) in the peptidergic nerve terminals. Amplitudes of both fast-inactivating ICa and long-lasting ICa were reduced in EtOH, and the reduction in ICa did not result from a shift in its current-voltage or steady-state inactivation relationships. Only the fast-inactivating component recovered after removal of EtOH. The effects of EtOH on ICa could not be attributed to changes in osmolarity. In contrast to ICa, the fast, transient K+ current was insensitive to EtOH. These results suggest that EtOH-induced reduction of ICa in the peptidergic nerve terminals produces a decrease in AVP release, resulting in lowered plasma AVP levels.