Unique residues in S4 affect accessibility and the shape of the gating-pore pathway. A. Representative traces from single mutants H325V and G331P illustrating the persistence of inward rectification and use of the gating-pore pathway. B. Current-voltage relationships for the inwardly rectifying single mutant channels. H325V (open circles) and H325E (black circles) have similar inward currents. H325V is a much weaker rectifier. The G331 single mutants are shown in red (G331P circles; G331A triangles) and the double mutant H325A+G331P is shown in grey triangles. The wild-type current-voltage relationship from 1B was renormalized with this dataset and is shown as a grey dashed line for reference. Error-bars have been removed for clarity. C. Permeation profiles for selected inward-rectifier channels. Permeability is shown as the fraction of the permeability of the channel to K+. n=4 for wild type, n=6 got G331A, n=6 for G331P, n=5 for H325E, n=7 for H325V, n=7 for H325R-G331R, n=6 for H325R-G331A, and n=6 for H325R-G331P. Error bars represent s.e.m.