Somatic outward currents in voltage clamp leech retzius nerve cell

Abstract

1. 1. Long-lasting depolarizing pulses in the point voltage experiments in leech Retzius neurons where the holding potential was more negative than — 40 mV induced a progressive decay of the outward current which could be satisfactorily described by a triple exponential function. 2. 2. By changing the level of the holding potential or frequency of stimulation it was possible to separate the total outward current into a fast and a slow one. A shift of 51 mV in the reversal potential of the fast outward current was obtained by a decade of changes in the external K. The estimated reversal potential of the slow outward current was very close to the theoretical equilibrium potential for K. 3. 3. Externally applied 10–20 mM TEA blocked the fast and slow outward current, in contrast to the action of 0.5–2 mM 4-aminopyridine, which was effective in blocking only the fast outward current. 4. 4. Complete blocking of the fast and partial reduction of the slow outward current after adding 1–2 mM M n to the external fluid was observed. 5. 5. The present experiments support the proposal of three classes of K channels in the soma membrane of leech Retzius neurons: (a) the fast, (b) the slow Ca-activated channel, and (c) the late voltage regulated potassium channels.