Slow low-threshold potassium current inHelix pomatia neurons

Abstract

A low-threshold outward current was studied in the neurons ofHelix pomatia at −70 to −30 mV using a two-electrode voltage clamp technique. In addition to the well-known A current (IA), a slower outward current calledIAs (slow) was revealed. Activation and inactivation times ofIAs at −40 mV ranged from 90 to 120 msec and from 3 to 5 sec, respectively. The current recovered within 2 to 5 sec after inactivation at −120 mV. Analysis of changes in the reversal potential ofIAs caused by an increase in external potassium concentration suggests a potassium origin forIAs. The curves ofIAs stationary activation and inactivation fit the Boltzmann equation. Deriving from an activation curve, the activation potential for a half-maximum current, , is −40 mV, and the slope factor,k, is −9.8 mV, while those values for the inactivation curve are −84 mV (a half-maximum inactivation) and 7.5 mV.IAs is blocked by 4-aminopyridine (1–30 µM), tetraethylammonium (1 mM), and Ba2+ (1 mM), but is resistant to Cs+ (1 mM). PeakIAs is not affected either by substitution of external Ca2+ for Mg2+ or by application of Cd2+ (0.5–1.0 mM). The results suggest that activation ofIAs does not require Ca2+ entry into the cell.