Single-channel analysis of fast transient potassium currents from rat nodose neurones.

Single channels that underlie the fast transient potassium current (IA) were recorded, using patch-clamp techniques, from cultured sensory neurones. The open channel conductance was approximately 22 pS, and was constant over most of the physiological voltage range; single-channel conductance decreased at more depolarized levels. Summing single-channel currents resulted in an average current whose kinetics were similar to the macroscopic IA. The inactivation of these currents, at the potentials we studied, was fitted with a single exponential with a time constant of approximately 30 ms. For the currents evoked by large depolarizing steps (to +40 mV), the mean channel open time equals approximately 30 ms. For currents evoked at less depolarized levels (to 0 mV), the mean open time equals approximately 15 ms, half the inactivation time constant.