SLOWLY INACTIVATING CALCIUM CURRENT IN MOLLUSCAN NEURONS .2. KINETICS AND STEADY-STATE PROPERTIES

1. 1. The process causing the slow calcium current decline during a long lasting depolarization was investigated in EDTA/EGTA injected cells. 2. 2. Intracellular EDTA or EGTA induced prolonged action potentials. The EDTA/EGTA plateaus were abolished by Co or La, they persisted in presence of 10-5 M TTX. 3. 3. Intracellular EDTA/EGTA increased the amplitude of the slow Ca current and shifted its reversal potential towards positive values. 4. 4. Substitution of calcium by barium in the external solution led to the same results as the EDTA/ EGTA injection. 5. 5. The experimental results were analyzed according to two hypotheses which could account for the slow current decline; shift of the Ca reversal potential or inactivating process. Tests performed in various conditions are in favour of a slow inactivating process. 6. 6. It is concluded that the Ca channel of Helix neurons has fast and slow inactivating processes. The slow Ca current is involved in the lengthening of the action potential during repetitive firing. © 1979.