Properties of single M-type KCNQ2/KCNQ3 potassium channels expressed in mammalian cells

1. The single channel properties of KCNQ2/KCNQ3 channels underlying neurona l voltage dependent M-type potassium currents were studied in cell-attached patches from transfected Chinese hamster ovary (CHO) cells. Macroscopic cu rrents produced by homo- and heteromeric KCNQ2/KCNQ3 channels were measured using the perforated-patch whole-cell technique. 2. Compared with heteromeric KCNQ2 + KCNQ3 channels, homomeric KCNQ2 channe ls had lower slope conductance (9.0 +/- 0.3 and 5.8 +/- 0.3 pS, respectivel y) and open probability at 0 mV (0.30 +/- 0.07 and 0.15 +/- 0.03, respectiv ely), consistent with their 3.8-fold Smaller macroscopic currents. By contr ast, homomeric KCNQ3 channels had the same slope conductance (9.0 +/- 1.1 p S) as KCNQ2 + KCNQ3 channels, and higher open probability (0.59 +/- 0.11), inconsistent with their 12.7-fold smaller macroscopic currents. Thus, KCNQ2 and KCNQ3 subunits may play different roles in the expression of M-type cu rrents, with KCNQ2 ensuring surface expression of underlying channels and K CNQ3 modifying their function. 3. Both in homo- and heteromeric KCNQ2/KCNQ3 channels the shut time distrib utions were fitted with three, and the open time distributions with two, ex ponential components. By measuring these and other parameters (e.g. conduct ance and open probability) KCNQ2/KCNQ3 channels can be shown to resemble pr eviously characterised neuronal M-type channels.