Table S1.

Electrophysiological parameters of WT and mutant I_KS channels under different internal recording solutions

Channel	Patch pipette solution	Current density (pA/pF) at +60 mV	V50 (mV)	Slope (mV)	n
WT IKS	5 μM Free Ca2+	299 ± 35	10.0 ± 2.8	12.8 ± 1.0	13
WT IKS	3 μM CaM + 5 μM free Ca2+	328 ± 42	0.7 ± 3.0	10.8 ± 1.0	7
WT IKS	5 mM BAPTA	128 ± 9*†	25.2 ± 2.4*†	14.9 ± 0.3	4
WT IKS	3 μM CaM + 5 mM BAPTA	103 ± 23***‡	22.4 ± 3.5***‡	12.0 ± 0.8	8
K526N and KCNE1	5 μM Free Ca2+	148 ± 29**†	37.6 ± 5.0***†	17.7 ± 1.7*†	5
K526E and KCNE1	5 μM Free Ca2+	114 ± 24***†	43.6 ± 4.2***†	22.3 ± 2.2***†	6
K527N and KCNE1	5 μM Free Ca2+	175 ± 25*†	20.1 ± 2.8*†	18.1 ± 2.2*†	6
K526N–K527N and KCNE1	5 μM Free Ca2+	35 ± 6***†	36.8 ± 2.5***†	17.4 ± 1.5	6

Significance level (*P < 0.05; **P < 0.01; ***P < 0.001) by unpaired two-tailed t test compared with control (WT I_KS recorded with 3 μM CaM and 5 μM free Ca²⁺) or WT I_KS recorded with 5 μM free Ca²⁺.

^†WT I_KS recorded with 5 μM free Ca²⁺.

^‡Control WT I_KS recorded with 3 μM CaM and 5 μM free Ca²⁺.