Sodium inward currents through calcium channels in mealworm muscle fibers

The contribution of Na⁺ ions to the nonsynaptic electrogenesis was studied in the larval muscle fibers of mealworm, Tenebrio molitor, using currentclamp and voltage‐clamp techniques. Na‐dependent graded responses were generated by depolarizing current stimuli in Ca²⁺‐free solutions. These responses were insensitive to tetrodotoxin and were blocked by Co²⁺. Large inward‐going currents were elicited by step depolarizations in Ca²⁺‐free solutions under voltage‐clamp conditions. The inward currents were totally eliminated by removal of Na⁺ from the bathing solution. These results indicate that the calcium channel of mealworm muscle is permeable to Na⁺.