Inactivation of a high conductance calcium dependent potassium current in rat hippocampal neurons

Abstract

Inactivating, high conductance BK-type currents have been recorded from inside-out patches (internal and external K + of 140 mM and 5 mM, respectively), obtained from cultured rat hippocampal neurons. The presence of prominent inactivation, not normally associated with BK channel activity, was dependent on two factors: a depolarizing step to 0 mV from a holding level of −80 mV and internal calcium at a concentration of 0.7 μM. Without the prior conditioning step to a negative potential, unitary currents were not evident at 0 mV; in addition, such currents were not elicited with the stimulus protocol if the internal Ca 2+ was reduced to a level of 0.3 μM. Concomitant with current inactivation was the finding of a delayed activation of BK currents following the depolarizing step. Higher internal calcium, at 100 μM, led to persistent and sustained channel activity at 0 mV which was not dependent on a prior step to −80 mV These results may be relevant to the complex nature of the repolarizing neuronal current Ic which is the macroscopic analogue of the unitary BK current.