[K-CHANNELS RESPONSIBLE FOR A-CURRENT IN RAT CA1 NEURONS(](OUT) ACCELERATES INACTIVATION OF SHAL)

SOMATO-DENDRITIC subthreshold transient potassium current (I-SA) was m easured in acutely isolated rat hippocampal CA1 pyramidal neurons. The inactivation of this current was insensitive to externally applied H2 O2 (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 inactivati on was measured at various [K+](out). Increase in [K+](out) leads to a cceleration 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 p reviously described action of [K+](out) on the inactivation of Shaker K+ channels.