Figure 5. Ko sensitivity of Na/K pump–mediated currents in Nai-loaded oocytes expressing WT or mutant Na/K pumps. (A) Changes in holding current at −50 mV in response to stepwise increments of [Ko] in C113Y Na/K pumps in 0 mM Nao; the vertical lines mark application of 100-ms voltage steps to −140 to 40 mV in 10-mV increments. (B) Steady-state I-V plots at the indicated [Ko] from A. (C and D) Corresponding Ko-modulated I-V plots (C) and ouabain-sensitive I-V plots (D) from data in A and B obtained by appropriate subtraction. (E–G) Analogous I-V plots to those in B–D, but for C113Y-ΔKESYY Na/K pumps in 125 mM Nao. (H–J) Hill fits to the Ko-modulated steady currents at the various [Ko] at each voltage yielded the mean K0.5(Ko) values for each pump type in the absence (open circles) or presence (closed circles) of Nao (WT, black; C113Y, red; RD, green; C113Y-ΔKESYY, blue; C113Y-ΔYY, olive; RD-ΔKESYY, magenta; RD-ΔYY, orange). Error bars represent SEM.
Figure 5.

Ko sensitivity of Na/K pump–mediated currents in Nai-loaded oocytes expressing WT or mutant Na/K pumps. (A) Changes in holding current at −50 mV in response to stepwise increments of [Ko] in C113Y Na/K pumps in 0 mM Nao; the vertical lines mark application of 100-ms voltage steps to −140 to 40 mV in 10-mV increments. (B) Steady-state I-V plots at the indicated [Ko] from A. (C and D) Corresponding Ko-modulated I-V plots (C) and ouabain-sensitive I-V plots (D) from data in A and B obtained by appropriate subtraction. (E–G) Analogous I-V plots to those in B–D, but for C113Y-ΔKESYY Na/K pumps in 125 mM Nao. (H–J) Hill fits to the Ko-modulated steady currents at the various [Ko] at each voltage yielded the mean K0.5(Ko) values for each pump type in the absence (open circles) or presence (closed circles) of Nao (WT, black; C113Y, red; RD, green; C113Y-ΔKESYY, blue; C113Y-ΔYY, olive; RD-ΔKESYY, magenta; RD-ΔYY, orange). Error bars represent SEM.

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