Two types of K+ channel subunit, Erg1 and KCNQ2/3, contribute to the M-like current in a mammalian neuronal cell

The potassium M current was originally identified in sympathetic ganglion c ells, and analogous currents have been reported in some central neurons and also in some neural cell lines. It has recently been suggested that the M channel in sympathetic neurons comprises a heteromultimer of KCNQ2 and KCNQ 3 (Wang et al., 1998) but it is unclear whether all other M-like currents a re generated by these channels. Here we report that the M-like current prev iously described in NG108-15 mouse neuroblastoma x rat glioma cells has two components, "fast" and "slow", that may be differentiated kinetically and pharmacologically. We provide evidence from PCR analysis and expression stu dies to indicate that these two components are mediated by two distinct mol ecular species of K+ channel: the fast component resembles that in sympathe tic ganglia and is probably carried by KCNQ2/3 channels, whereas the slow c omponent appears to be carried by merg1a channels. Thus, the channels gener ating M-like currents in different cells may be heterogeneous in molecular composition.