INVOLVEMENT OF CLASS-A CALCIUM CHANNELS IN THE KCL INDUCED CA2+ INFLUX IN HIPPOCAMPAL SYNAPTOSOMES

Using Ca2+ channel toxins, we determined the types of voltage-sensitive calcium channels activated by two levels of KCI depolarization in hippocampal synaptosomes. The increase in the intracellular Ca2+ concentration ([Ca2+](i)) induced by 30 mM KCI was equally sensitive to either omega-agatoxin IVA (omega-Aga IVA) or to omega-conotoxin MVIIC (omega-CgTx MVIIC), and the inhibition produced by these two peptides was not additive. The present results indicate that omega-Aga IVA and omega-CgTx MVIIC do not distinguish between two different VSCC in hippocampal synaptosomes and that they both inhibit a channel with the alpha(1A) subunit which is present in the rat hippocampus.