The CLH-3b S747E mutant is inhibited by GCK-3. (A) Current-to-voltage relationships of the S747E mutant coexpressed with functional or KD GCK-3. Coexpression of S747E with GCK-3 significantly (P < 0.02) reduced current density over the entire range of potentials where the channels were active. Values are means ± SE (n = 8–14). (B) Activation voltages and 50% rise times of whole cell currents in cells coexpressing the S747E mutant and KD GCK-3 or GCK-3. GCK-3 significantly (P < 0.002) increased activation voltage and 50% rise time. Values are means ± SE (n = 8–14). *, P < 0.001 and **, P < 0.002 compared with KD GCK-3. (C) Effect of cell swelling on current amplitude in cells coexpressing the S747E mutant and KD GCK-3 or GCK-3. Inhibition of whole cell current amplitude by GCK-3 was not altered significantly (P > 0.1) by cell swelling. Values are means ± SE (n = 14). Data were obtained as described in the legend to Fig. 1.