Interactions among Inactivating and Noninactivating Kvβ Subunits, and Kvα1.2, Produce Potassium Currents with Intermediate Inactivation

Experiments were carried out to determine whether coinjection of Kvalpha1.2 with inactivating and noninactivating Kvbeta subunits would produce currents with intermediate kinetics and channel complexes containing a mixture of these subunits. Upon coexpression with a saturating amount of Kvbeta1.2 and increasing levels of a noninactivating deletion mutant of Kvbeta1.2, we show that macroscopic Kvalpha1.2 currents have levels of fractional inactivation and inactivation time constants that are intermediate between those obtained with either the inactivating Kvbeta1.2 or the noninactivating Kvbeta1.2 mutant. We also find that coexpression of Kvalpha1.2 with saturating amounts of Kvbeta1.2 and the deletion mutant produces a population of single channels with properties intermediate to either the inactivating or noninactivating parental phenotype. Our data can best be explained by the presence of an intermediate population of heterooligomeric channels consisting of Kvalpha1.2 with different combinations of both types of subunits. Since Kvalpha1.2 subunits coexist in cells with inactivating and noninactivating Kvbeta subunits, our findings suggest that heterooligomeric assembly of these subunits occurs to increase the range of K+ current kinetics and expression levels.