Fig. 2

Gating currents of SpSLC9C1. Voltage protocol, gating currents, and charge–voltage (Q/V) relation. The solid curve in the Q/V relations (insets) represents a Boltzmann fit. a Upper: wt SpSLC9C1 without cNMP (V_1/2 = −91.4 mV, slope s = 9.2 mV). Middle: non-transfected CHO cells. Lower: wt SpSLC9C1, 1 mM cAMP in the pipette solution (V_1/2 = −75.4 mV, s = 8.2 mV). b Q/Q_max vs. V_m relation. Mean ± SD (n = number of experiments) of V_1/2 and slope s was determined by a Boltzmann fit (w/o cNMP: −94.7 ± 2.9 mV, s = 8.5 ± 0.8 mV, q_g = 3.1 e₀, n = 6; cAMP: −74.4 ± 6.4 mV, s = 8.8 ± 1.9 mV, q_g = 2.9 e₀, n = 7; cGMP: −86.9 ± 3.0 mV, s = 8.3 ± 1.0 mV, q_g = 3.1 e₀, n = 7). c Replacing Arg803 in S4 by Gln (R803Q) shifted V_1/2 by −24 mV and s by 5 mV (V_1/2 = −117.9 ± 7.1 mV, s = 13.0 ± 1.1 mV, q_g = 2.0 e₀, n = 7). This mutation did not affect V_1/2 modulation by 1 mM cAMP (V_1/2 = −96.8 ± 6.6 mV, s = 13.5 ± 2.6 mV, q_g = 1.9 e₀, n = 6). Gray line: voltage dependence of wt SpSLC9C1 without cNMP. d Replacing Arg1053 in the CNBD by Gln (R1053Q) does not affect V_1/2 without cNMP (−93.4 ± 1.7 mV, s = 9.4 ± 2.0 mV, q_g = 2.8 e₀, n = 6), but strongly reduced V_1/2 shift by cAMP (V_1/2 = −93.9 ± 4.2 mV, s = 10.3 ± 1.0 mV, q_g = 2.5 e₀, n = 5). Gray line: voltage dependence of wt SpSLC9C1 with cNMP. e In the NHE-domain mutant (R399A), Na⁺/H⁺ exchange is abolished (Fig. 5), but not gating currents (Supplementary Figure 4). V_1/2 in the absence (−87.3 ± 2.8 mV, s = 10.4 ± 1.8 mV, q_g = 2.5 e₀, n = 3) and presence of cAMP (−76.5 ± 9.6 mV, s = 6.0 ± 0.8 mV, q_g = 4.3 e₀, n = 5). Gray line: voltage dependence of wt SpSLC9C1 without cNMP