Fig. 5.

Functional measurements of NKA-mediated Na⁺ efflux in HEK293 cells. (A) Experimental protocol: NKA was first inhibited (K⁺-free external solution) causing cellular [Na⁺]_i loading, then NKA was reactivated by 4 mM K⁺. One micromole of ouabain was used throughout to inhibit endogenous human NKA. (B–E) NKA-mediated Na⁺ extrusion curves and mean K_0.5 comparing Na⁺ extrusion in HEK293 cells expressing WT–NKA (B and C) vs. E960A–NKA (D and E). V_max and K_0.5 were derived by fitting the curves with a Hill equation. *P < 0.05. Corresponding n are indicated below bars; error bars indicate SEM.