PROPERTIES OF SLOW EARLY POTASSIUM CURRENT IN NEURONS OF SNAIL HELIX-POMATIA

1. In isolated neurons of visceral ganglia of snail Helix pomatia a sl ow early outward current (I-As) was studied using a two-microelectrode voltage clamp technique. 2. The time of activation and inactivation o f I-As at -40 mV were 90-120 msec and 3-5 sec respectively. The remova l of inactivation at -120 mV took 2-5 min.3. The reversal potential of the I-As was about -80mV in normal saline and was sensitive to the ex ternal potassium concentration, changing about 35 mV per fivefold chan ge in potassium over the range from 4 to 20 mM. The results suggest th at I-As were due to K+. 4. The I-As persisted in Ca2+-free medium and in the presence of Ca2+-channels blockers, e.g., Cd2+. 5. The I-As wer e blocked by 1-10 mu M extracellular 4-aminopyridine, 1 mM of tetraeth ylammonium ions, 1 mM of Ba2+, but one was resistant to I mM Cs+. 6. 4 -aminopyridine had a dual effect on the I-As. It blocked the normal cu rrent, and then appeared to increase the inactivated currents.