Figure 2. Determination of steady-state Na/K pump current of WT and ouabain-resistant RD and C113Y mutant pumps in the presence and absence of external Na (replaced by TMA). (A) Representative record of current changes at the −50-mV holding potential in a Na-loaded oocyte expressing RD Na/K pumps caused by addition of 15 mM Ko and/or 10 mM ouabain in the presence and then in the absence of Nao as indicated; the vertical lines mark application of 100-ms voltage steps to −180 to 60 mV in 20-mV increments. (B) Selected superimposed current traces from the experiment in A obtained at the times identified on the recording by the red numbers. Analogous traces are superimposed for C113Y (D) and WT (F) pumps. The corresponding steady-state (mean of last 10 ms of each step) current–voltage (I-V) relationships for each Na/K pump type, obtained from the records in B, D, and F, are shown in C, E, and G.
Figure 2.

Determination of steady-state Na/K pump current of WT and ouabain-resistant RD and C113Y mutant pumps in the presence and absence of external Na (replaced by TMA). (A) Representative record of current changes at the −50-mV holding potential in a Na-loaded oocyte expressing RD Na/K pumps caused by addition of 15 mM Ko and/or 10 mM ouabain in the presence and then in the absence of Nao as indicated; the vertical lines mark application of 100-ms voltage steps to −180 to 60 mV in 20-mV increments. (B) Selected superimposed current traces from the experiment in A obtained at the times identified on the recording by the red numbers. Analogous traces are superimposed for C113Y (D) and WT (F) pumps. The corresponding steady-state (mean of last 10 ms of each step) current–voltage (I-V) relationships for each Na/K pump type, obtained from the records in B, D, and F, are shown in C, E, and G.

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