[K+]out accelerates inactivation of Shal-channels responsible for A-current in rat CA1 neurons.

Somato-dendritic subthreshold transient potassium current [I(SA)] was measured in acutely isolated rat hippocampal CA1 pyramidal neurons. The inactivation of this current was insensitive to externally applied H2O2 (20 mM) which causes cysteine oxidation. This result suggests that Shal-channels not Shaker Kv1.4 channels underlie the somato-dendritic I(SA) in rat CA1 pyramidal neurons. The kinetics of the I(SA) inactivation was measured at various [K+]out. Increase in [K+]out leads to acceleration of Shal-channel inactivation. Thus, the shift in [K+]out from 1 to 50 mM results in decreased inactivation time constant from 37 to 19 ms. This effect of [K+]out on the I(SA) is opposite to the previously described action of [K+]out on the inactivation of Shaker K+ channels.