Inward-rectifying potassium channels located in the plasma membrane of higher plant and animal cells contribute to cellular homeostasis and excitability. The genes encoding this specific class of K+ channels have not been functionally identified. This report shows that a single messenger RNA transcript from the Arabidopsis thaliana KAT1 complementary DNA confers the functional expression of a hyperpolarization-activated K+ channel in Xenopus oocytes. The channels encoded by KAT1 are highly selective for K + over other monovalent cations, are blocked by tetraethylammonium and barium, and have a single-channel conductance of 28 ± 7 picosiemens with 118 millimolar K+ in the bathing solution. These functional characteristics, typical of inward-rectifying K+ channels in eukaryotic cells, demonstrate that KAT1 encodes an inward-rectifying K + channel.
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