Figure 4.

SMIT1 positive-shifts and slows KCNQ1-KCNE1 activation. (A) Representative traces from TEVC recordings of Xenopus laevis oocytes injected with cRNA encoding KCNQ1 (Q1), alone or co-injected with cRNA encoding SMIT1 (S1); n = 97–102. The inset shows the voltage protocol. (B) Mean peak current-voltage relationship for subunit combinations as in (A); n = 97–102. Error bars indicate the mean ± SE. (C) Mean normalized tail current (at −30 mV) versus pre-pulse potential for oocytes as in (A); n = 97–102. Error bars indicate the mean ± SE. (D) Representative traces from TEVC recordings of Xenopus laevis oocytes injected with cRNA encoding KCNQ1/KCNE1 (Q1/E1), alone or co-injected with cRNA encoding SMIT1 (S1); n = 90–100. The inset shows the voltage protocol. (E) Mean peak current-voltage relationship for subunit combinations as in (D); n = 90–100. Error bars indicate the mean ± SE; ^∗∗∗p < 0.0001; ^∗∗∗∗p < 0.00001. (F) Mean normalized tail current (at −30 mV) versus pre-pulse potential for oocytes as in (D); n = 90–100. Error bars indicate the mean ± SE. (G) Representative traces from TEVC recordings of Xenopus laevis oocytes injected with cRNA encoding KCNQ1/KCNE1 (Q1/E1), alone or co-injected with cRNA encoding SMIT1 (S1); n = 12, using longer (10 s) prepulses than in (D) and pulsing to +60 mV (voltage protocol in lower inset). (H) Mean peak current-voltage relationship for subunit combinations as in (G); n = 12. Error bars indicate the mean ± SE; ^∗p < 0.05; ^∗∗p < 0.01; ^∗∗∗p < 0.0001. (I) Mean normalized tail current (at −30 mV) versus pre-pulse potential for oocytes as in (G); n = 12. Error bars indicate the mean ± SE. (J) Normalized, averaged traces from recordings as in (A) (left) and (G) (right), to illustrate slowed KCNQ1/KCNE1 (Q1/E1) activation due to SMIT1 (S1) co-expression; n = 12. (K) Mean activation (left) and deactivation (right) rates for traces as in (G); n = 12. Error bars indicate the mean ± SE; ^∗p < 0.05; ^∗∗p < 0.01; ^∗∗∗p < 0.001.