M335A increases the sodium sensitivity of Slack channel mutants. A, Sample current traces recorded in the inside-out patch configuration for Y375A. The ramp protocol ran from −100 to +100 mV. B, Sample current traces recorded in the inside-out patch configuration for the Y375A/M335A mutant with a ramp protocol ran from −100 to +100 mV. C, Hill equation fits the Na+ dose dependence data of Y375A and Y375A/M335A mutants. D, Comparison of EC50 values of the sodium dependence of L371A to Y375A with the EC50 values of the sodium dependence of double mutants of M335A plus corresponding mutants from L371A to Y375A. E, Hill equation fits the Na+ dose dependence data of M335A/D955N and M335A/E491Q. F, Comparison of minimum EC50 values of sodium dependence of E490Q, E491Q, E787Q, E899A, and D955N with the minimum EC50 values of sodium dependence of M335A/E490Q, M335A/E491Q, M335A/E787Q, M335A/E899A, and M335A/D955N.