Inactivating and non-inactivating outward current channels in cell-attached patches of Helix neurons.

Two species of inactivating outward current channels and a non-inactivating voltage-dependent current were seen in cell-attached patches of Helix neurons. Large, slowly inactivating channels had a slope conductance of 44 pS as measured with patch pipets containing the normal extracellular ion concentrations, including 4 mM potassium. Latency to maximal opening was 50-220 ms, and the inactivation time constant averaged 350 ms. Channel opening was decreased by preceding depolarization. The channels were selective for potassium and inhibited by 50 mM TEA. Small, quickly inactivating channels were 14 pS and had kinetics and voltage dependence similar to IA. Patch depolarization also activated a non-inactivating voltage-dependent outward current having channel conductance and/or kinetics such that individual channel openings and closings could not be distinguished. Such current was also seen in the presence of 50 mM TEA, but not in the presence of Co2+, characteristics which are similar to outward hydrogen ion currents, described by others in Helix neurons.