The CLH-3b S742E mutant is inhibited by GCK-3. (A) Current-to-voltage relationships of the S742E mutant coexpressed with functional or KD GCK-3. Coexpression of S742E with GCK-3 significantly (P < 0.01) reduced current density over the entire range of potentials where the channels were active. Values are means ± SE (n = 7–16). (B) Activation voltages and 50% rise times of whole cell currents in cells coexpressing the S742E mutant and KD GCK-3 or GCK-3. Values are means ± SE (n = 7–16). *, P < 0.001 compared with KD GCK-3 isotonic. **, P < 0.002 compared with GCK-3 isotonic. (C) Effect of cell swelling on current amplitude in cells coexpressing the S742E mutant and KD GCK-3 or GCK-3. Values are means ± SE (n = 16). *, P < 0.02. Data were obtained as described in the legend to Fig. 1.