Differential Effects of Lipid-soluble Toxins on Sodium Channels and L-type Calcium Channels in Frog Ventricular Cells

The effect of grayanotoxin I (GTX I), veratridine and aconitine with either an external or internal concentration of 100 μM on L-type calcium (Ca) channels was studied using the whole cell patch clamp and internal dialysis methods. The experimental conditions for the modification of sodium (Na) channels induced by the internal application of these toxins was determined by showing sustained inward currents with depolarizing repetitive pulses. These toxins failed to generate any change in Ca channels under the same experimental protocol as for Na channels. However, external application of these toxins caused a moderate block of the Ca channels without changing the kinetics.