Oocytes were injected with Xenopus Kv2.2 RNA alone or in a 1:1 ratio with each Kv2.2 mutant clone, as described in Materials and Methods. Coexpression of wild-type and mutant XenopusKv2.2 RNAs should lead to the formation of wild-type or mutant homomultimers and channels composed of one, two, or three mutant subunits. The binomial equation (MacKinnon, 1991) (see Materials and Methods) was used to calculate the percentage of each channel type expected to form and thus the percentage of wild-type current that would be measured if two or three mutant subunits suffice to render heteromultimeric channels nonfunctional. To normalize current amplitudes that varied between experimental days, we determined for each day the average current amplitude recorded from control oocytes injected with wild-type Kv2.2 RNA alone and then expressed the result recorded from each oocyte injected with a mixture of wild-type and mutant RNA as a fraction of the control current recorded that day. Control oocytes and those injected with a mixture of wild-type and mutant Kv2.2 RNAs were obtained from the same frog. Current amplitudes are taken at +20 mV and are given as means ± SEM. NA, Not applicable.