Omega-conotoxin GVIA and dihydropyridines discriminate two types of Ca2+ channels involved in GABA release from striatal neurons in culture.

We previously reported that the opening of the L-type Ca2+ channel was only partly involved in the K(+)-evoked Ca2(+)-dependent gamma-aminobutyric acid (GABA) release from striatal neurons, suggesting that probably different types of voltage-sensitive Ca2+ channels were implicated in this physiological process. Here we demonstrate that omega-conotoxin GVIA, which has been reported to block L- and N-type neuronal Ca2+ channels, also partly inhibits the Ca2(+)-dependent GABA release. The maximal effects of omega-conotoxin GVIA and nifedipine, a highly specific antagonist of the L-type channels, were additive, a total inhibition of the Ca2(+)-dependent GABA release being obtained in the presence of both drugs. We therefore propose that omega-conotoxin GVIA and nifedipine block two different types of Ca2+ channels, both involved in the GABA release process.