Calcium and sodium ions as charge carriers in the action potential of an identified snail neurone.

1. The soma of cell A in Helix aspersa produced action potentials in sodium‐free or calcium‐free saline, but not in saline with neither sodium nor calcium. 2. The axon had a sodium‐dependent action potential. 3. Tetrodotoxin (5 x 10(−6) M) had no effect on the overshoot except at low external divalent ion concentrations. 4. The action potential in sodium‐free saline was blocked by cobalt. 5. The slope of action potential overshoot against sodium concentration in the presence of 10 mM calcium was 10.5 mV/tenfold change. That of overshoot against calcium concentration in the presence of 75 mM sodium was 22 mV/tenfold change. 6. In sodium‐free saline the slope of overshoot versus calcium concentration was 27 mV/tenfold change. 7. It is concluded that calcium is an important charge carrier in the action potential of cell A.

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