Selective Expression in Carotid Body Type I Cells of a Single Splice Variant of the Large Conductance Calcium- and Voltage-activated Potassium Channel Confers Regulation by AMP-activated Protein Kinase

Inhibition of large conductance calcium-activated potassium (BK(Ca)) channels mediates, in part, oxygen sensing by carotid body type I cells. However, BK(Ca) channels remain active in cells that do not serve to monitor oxygen supply. Using a novel, bacterially derived AMP-activated protein kinase (AMPK), we show that AMPK phosphorylates and inhibits BK(Ca) channels in a splice variant-specific manner. Inclusion of the stress-regulated exon within BK(Ca) channel α subunits increased the stoichiometry of phosphorylation by AMPK when compared with channels lacking this exon. Surprisingly, however, the increased phosphorylation conferred by the stress-regulated exon abolished BK(Ca) channel inhibition by AMPK. Point mutation of a single serine (Ser-657) within this exon reduced channel phosphorylation and restored channel inhibition by AMPK. Significantly, RT-PCR showed that rat carotid body type I cells express only the variant of BK(Ca) that lacks the stress-regulated exon, and intracellular dialysis of bacterially expressed AMPK markedly attenuated BK(Ca) currents in these cells. Conditional regulation of BK(Ca) channel splice variants by AMPK may therefore determine the response of carotid body type I cells to hypoxia.