Effect of FXYD isoforms on turnover rate. Mean turnover rate at 4.5 mM K⁺_o as a function of voltage. Error bars are SEM. Data from Warner amplifier are shown. Values at 0 mV are (± SD in s⁻¹): 14.9 ± 3.0 (n = 47, data from Warner and Dagan amplifiers) for α1β1, 12.9 ± 3.0* for α1β1FXYD1 (n = 20, data from Warner and Dagan amplifiers), 12.8 ± 3.9 for α1β1FXYD2, 14.7 ± 3.3 for α1β1FXYD4, 19.1 ± 3.1 for α1β1FXYD6**, and 13.3 ± 1.7 for α1β1FXYD7. Note that there are more oocytes where we measured pump current at 4.5 mM K⁺_o and charge movement than full dose–response curves and charge movement. Significantly different with respect to α1β1 alone by t test: *, P < 0.05; **, P < 0.001.