Apparent affinity of the Na,K-ATPase α2 isozyme for K⁺. (A) Representative traces of Ip elicited by consecutive extracellular K⁺ concentration changes from 0 to 2, 4, 10, 20, and 40 mM. (B) Current records from the same fiber after the addition of 10 µM ouabain. Current is plotted on same scale as A, but using a different time scale. The timing of the [K⁺] changes was approximated to align with the perfusion-dependent current artifacts. (C) Mean Ip values (n = 18 fibers) at each K⁺ concentration were normalized to the mean Ip at 40 mM K⁺ and fit to the Hill equation. The Hill coefficient was constrained to 1.68. Temperature, 22°C. Error bars represent mean ± SEM.