Figure 8.

K⁺_o dependence of wild-type and G99R pumps. (A and B) TEVC recordings at −50 mV from representative oocytes 4–5 d after injection with wild-type (A) or G99R (B) cRNA. Application of K⁺_o in Na⁺_o solution stimulated outward current in a [K⁺_o]-dependent manner. Addition of 10 and 20 mM K⁺_o did not activate outward current after application and withdrawal of 1 mM ouabain. Insets in A and B are the expanded time-scale ouabain-sensitive transient currents in Na⁺_o upon 100-ms voltage steps from −50 mV. (C) Mean K_0.5 for K⁺_o, as a function of voltage, for wild type (squares) and G99R (circles), measured in 125 mM Na⁺_o (open symbols) or 150 mM Na⁺_o (solid symbols). Wild type at 125 mM Na⁺_o (n = 6) and at 150 mM Na⁺_o (n = 4); G99R at 125 mM Na⁺_o (n = 3) and at 150 mM Na⁺_o (n = 8). (D) Mean normalized Q-V curves in 125 mM Na⁺_o for wild type (squares, n = 7) and G99R (circles, n = 6). Line plots represent a Boltzmann with parameters in the text. Error bars in C and D are SEM, smaller than the symbols for most data points.