POTASSIUM CURRENTS IN ACUTELY ISOLATED MATURING RAT HIPPOCAMPAL CA1 NEURONS

Whole-cell voltage clamp techniques were used to characterize the post natal development of current amplitude and inactivation and activation kinetics of two potassium currents in acutely isolated CA1 cells from rats P4 to P52: the A-current (I) and a slow-rising, slow inactivatin g current (I-K). In the course of maturation, changes in the relative proportion of I-A and I-K currents were observed, the latter becoming a dominant current in older cells. The half-maximal point (V-h,) of st eady-state inactivation and activation of I-A and I-K shifted in the c ourse of the first and second postnatal weeks. The shifts were hyperpo larizing in the case of I-K, whereas I-A Shifted to less negative valu es. The shifts in steady-state inactivation V-h were accompanied by a change in the slope factor (V-s), which is an indication of a modifica tion in the voltage sensitivity of the steady-state inactivation. The kinetics of I-K evolve after birth in a fashion that matches the chang es in action potential parameters previously reported.