**Properties of currents recorded in oocytes injected with different cRNAs encoding single or tandem subunits.** *A*, typical ionic currents recorded in oocytes injected with *KAT1* or *KAT2* cRNA or different tandem constructs (*KAT1-KAT1*, *KAT2-KAT2*, *KAT2-KAT1*, and *KAT1-KAT2*). Macroscopic currents were recorded with the voltage-clamp technique in 100 mm K^{+} external solution. In all recordings, the holding potential was −40 mV, and 1.7-s voltage pulses were applied to values ranging between +40 and −200 mV with −15-mV decrements. *B*, comparison of the functional properties of KAT1 (*white bars*), KAT2 (*black bars*), and KAT1 + KAT2 currents (*gray bars*). The gating parameters (*z*_{g} and *E*_{a}_{50}) were obtained from the best fit with a Boltzmann distribution of the open probability as described previously (39), and each value represents the mean ± S.E., with *n* = 22, 36, 25, 18, 50, and 46 oocytes expressing *KAT2-KAT1*, *KAT1-KAT2*, *KAT1*, *KAT2*, *KAT1-KAT1*, and *KAT2-KAT2* cRNAs, respectively. *t*½ activation is the time for half-activation in response to a voltage step from −40 to −170 mV (mean ± S.E., with *n* = 16, 26, 11, 16, 31, and 42 oocytes expressing *KAT2-KAT1*, *KAT1-KAT2*, *KAT1*, *KAT2*, *KAT1-KAT1*, and *KAT2-KAT2* cRNAs, respectively). τ deactivation is the time for half-deactivation derived by fitting decaying monoexponential functions to the tail currents (recorded on return to the holding potential; mean ± S.E., with *n* = 20, 30, 15, 11, 32, and 37 oocytes expressing *KAT2-KAT1*, *KAT1-KAT2*, *KAT1*, *KAT2*, *KAT1-KAT1*, and *KAT2-KAT2* cRNAs, respectively). *Two identical letters* above the bars indicate no statistically different data sets (*p* > 0.95, Student's *t* test).

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