[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.