Effect of FXYD subunits on transient currents. (A–F) Ouabain-sensitive currents elicited by voltage steps from the holding potential to −100 and +40 mV recorded from oocytes bathed in external Na⁺ solution 3–6 d after injection with α1β1 (A), α1β1FXYD1 (B), α1β1FXYD2 (C), α1β1FXYD4 (D), α1β1FXYD6 (E), or α1β1FXYD7 (F). The oocyte in B was held at −35 mV, and the rest were held at −50 mV. Depolarizing voltage pulses from the holding potential produce transient outward currents, whereas hyperpolarizing voltage pulses produce transient inward currents. The dashed lines are monoexponential fits to the current, beginning 3 ms after the voltage step.