Figure 2. I_p-V relationships at various [Na⁺]_pip.

Na⁺-K⁺ pump currents normalized to cell capacitance are plotted versus membrane potential. A, I_p-V relationships at 0 mM (▿), 0.5 mM (⋄), 2 mM (▵), 5 mM (○), and 50 mM (□) Na⁺_pip in cells dialysed with NMDG⁺-containing pipette solution (n = 4–8). B, corresponding I_p-V curves for myocytes containing TEA⁺ as the main cation (n = 4–7). Symbols have the same meaning as in A. Note the absence of I_p in Na⁺-free pipette solutions and the voltage dependence of I_p at low (< = 5 mM) Na⁺_pip. In contrast, I_p activated by 50 mM Na⁺_pip is voltage insensitive.