Figure 3.

Double mutants with M335A show functional expression but decreased sodium sensitivity. A, Sample single-channel current of M335A mutant with 0 mm intracellular sodium and macroscopic typical current traces with 500 mm cytosolic Na⁺ were recorded in the inside-out patch configuration. A, −100 mV hyperpolarization generated the currents. B, Sample current traces of M335A with 50–500 mm cytosolic Na⁺ are shown. Currents were generated by a −100 to +100 mV ramp protocol. C, Sodium sensitivity of rSlack channel and M335A mutants were estimated by Hill equation fitted data. D, Sample current traces of the M335A/E865Q mutant were recorded in the inside-out patch configuration. E, Hill equation fitted the data of the Na⁺ dose response of D863N/M335A [minimum EC₅₀ = 1154 ± 17.5 mm, coefficient factor (cf) = 4], E865Q/M335A (minimum EC₅₀ = 1430 ± 73.2 mm, cf = 4), and D1196N/M335A (EC₅₀ = 82.6 ± 2.6 mm, cf = 4) mutants. F, Summary of EC₅₀ and minimum EC₅₀ values for the wild-type Slack channel, M335A (EC₅₀ = 49 ± 3 mm, cf = 4), M335A/D863N, M335A/E865Q, and M335A/D1196N.