Immature Maxi-K Channels Exhibit Heterogeneous Properties in the Embryonic Rat Telencephalon

Using the cell-attached configuration of the patch-clamp technique, we recorded large-conductance K channels (LCKs) from intact telencephala and cortical slices of embryonic (E) 12-14 and E21 rats, respectively. Conductance (about 200 pS with K(+)-rich pipettes), kinetics and sensitivity to fatty acids (FAs) were reminiscent of some features of the Ca-activated 'maxi-K' channel (BK), yet less than half the LCKs were Ca-sensitive. At E12-14, an even smaller proportion of the channels were strictly voltage-sensitive, that proportion rising to about 50% at E21. Ca and voltage sensitivities were observed independent of one another. The open probability of voltage-sensitive LCKs increased exponentially with depolarization rates similar to those reported for classical BKs. It is postulated that embryonic LCKs may constitute immature forms of BKs whose gating is regulated by endogenous FAs.