Interaction of steroidal alkaloid toxins with calcium channels in neuronal cell lines

Depolarization with 50 mM K⁺ increased ⁴⁵Ca²⁺ uptake into neuronal clonal cell lines NG108-15, NIE-115 and NH15-CA2. In each cell line this depolarization-induced uptake was blocked by inorganic and organic blockers of voltage sensitive calcium channels. However, tetrodotoxin (10^-6M) was ineffective. Moreover, in the presence of tetrodotoxin, neither batrachotoxin nor veratridine inhibited the depolarization-induced uptake. The novel dihydropyridine BAY K8644 enhanced depolarization-induced ⁴⁵Ca²⁺ uptake into each cell line in a nitrendipine reversible fashion. In the presence of tetrodotoxin, the BAY K8644/50 mM K⁺ stimulated uptake could be partially inhibited by batrachotoxin (10^-6M) and veratridine (5 x 10^-5 M). These effects were not altered by the presence of scorpion venom (1 μg/ml). The results indicate that both batrachotoxin and veratridine can modulate the affects of dihydropyridines on the gating properties of voltage sensitive calcium channels.