FXYD effects on Na/K pump interaction with Na⁺_i in the presence of NMDG⁺_i (without K⁺_i). (A) Representative patch from an oocyte expressing α1β1 alone held at 0 mV with extracellular solution containing 5 mM K⁺_o in NMDG⁺_o. The bars on top indicate [Na⁺]_i (in mM), and the bars under the traces indicate application of MgATP (4 mM) to activate outward Na/K pump current. Note the biphasic activation, more obvious in first ATP application. Vertical deflections correspond to application of 25-ms-long voltage pulses. (B) Mean ATP-induced current as a function of [Na⁺]_i. Line plots are Hill equations with the parameters in Table 3. (C)K_0.5,Na+ for each FXYD. Error bars are SEM.