…et al., 1989), increasing permeant ion concentration (Green et al., 1987; MacKinnon and Miller, 1988; Giangiacomo et al., 1992; Murrell-Lagnado and Aldrich, 1993b) or by introducing, and altering the concentration of, an ‘‘inert’’ cation (Anderson et al., 1988; Lucchesi and Moczydlowski, 1991).