Single-channel basis for conductance increase induced by isoflurane in Shaker H4IR K+ channels

Volatile anesthetics modulate the function of various K+ channels. We previously reported that isoflurane induces an increase in macroscopic currents and a slowing down of current deactivation of Shaker H4 IR K+ channels. To understand the single-channel basis of these effects, we performed nonstationary noise analysis of macroscopic currents and analysis of single channels in patches from Xenopus oocytes expressing Shaker H4 IR. Isoflurane (1.2% and 2.5%) induced concentration-dependent, partially reversible increases in macroscopic currents and in the time course of tail currents. Noise analysis of currents (70 mV) revealed an increase in unitary current (similar to 17%) and maximum open probability (similar to 20%). Single-channel conductance was larger (similar to 20%), and opening events were more stable, in isoflurane. Tail-current slow time constants increased by 41% and 136% in 1.2% and 2.5% isoflurane, respectively. Our results show that, in a manner consistent with stabilization of the open state, isoflurane increased the macroscopic conductance of Shaker H4 IR K+ channels by increasing the single-channel conductance and the open probability.