SLOWLY INACTIVATING CALCIUM CURRENT IN MOLLUSCAN NEURONS .1. SLOW CURRENTS DURING LONG-LASTING VOLTAGE CLAMP PULSES

1. 1. The plateau of prolonged spikes of TEA-treated Helix neurons are reversibly shortened by repeated activation and by extracellular Cd or Co. 2. 2. Long voltage clamp pulses (up to 25 sec) induce slow current changes; they are followed by a slow tail current. 3. 3. When considering only the slow current changes during and after the pulses, the current voltage relationship is N-shaped. The N-shape is strongly attenuated by cobalt. 4. 4. The slow tail current reverses at about -50 mV and it is inhibited by TEA. 5. 5. The slow current during the pulse persists in TEA-saline, with 10-5 M TTX and when Na and Mg were replaced by Tris. It is abolished by calcium free saline and by Co, La, Mn, Cd and mephenesin. 6. 6. It is concluded that the slow current produced by sustained depolarizations is due to the slow decrease of an inward Ca current which causes the plateau of TEA treated neurons. © 1979.