Suppression of inward-rectifying K+ channels KAT1 and AKT2 by dominant negative point mutations in the KAT1 alpha-subunit

The Arabidopsis thaliana cDNA, KAT1 encodes a hyperpolarization-activated K + (K-in(+)) channel. In the present study, we identify and characterize dom inant negative point mutations that suppress K-in(+) channel function. Effe cts of two mutations located in the H5 region of KAT1, at positions 256 (T2 56R) and 262 (G262K), were studied. The co-expression of either T256R or G2 62K mutants with KAT1 produced an inhibition of K+ currents upon membrane h yperpolarization. The magnitude of this inhibition was dependent upon the m olar ratio of cRNA for wild-type to mutant channel subunits injected. Inhib ition of KAT1 currents by the co-expression of T256R or G262K did not great ly affect the ion selectivity of residual currents for Rb+, Na+, Li+, or Cs +. When T256R or G262K were coexpressed with a different K+ channel, AKT2, an inhibition of the channel currents was also observed. Voltage-dependent Cs+ block experiments with co-expressed wild type, KAT1 and AKT2, channels further indicated that KAT1 and AKT2 formed heteromultimers. These data sho w that AKT2 and KAT1 are able to co-assemble and suggest that suppression o f channel function can be pursued in vivo by the expression of the dominant negative K-in(+) channel mutants described here.