Interacting effects of N-terminal variation and strex exon splicing on slo potassium channel regulation by calcium, phosphorylation, and oxidation

Abstract

We have investigated the structural basis for the phenotype of a native rat Slo (rSlo) potassium channel (BKCa; KCNMA1) in a rat pituitary cell line, GH4C1. Opposing regulation of these calcium- and voltage-activated potassium channels by cAMP- and cGMP-dependent protein kinases requires an alternatively spliced exon (strex) of 59 amino acids in the cytoplasmic C terminus of the pore-forming α subunit encoded by rslo. However, inclusion of this cysteine-rich exon produces a 10-fold increase in the sensitivity of the channels to inhibition by oxidation. Inclusion of the strex exon also increases channel sensitivity to stimulation by calcium, but responses in the physiological ranges of calcium and voltage require coassembly with β1 subunits. With strex present, however, β1 subunits only stimulated channels assembled from rSlo α subunits with a truncated N terminus beginning MDALI-. Thus N-terminal variation and strex exon splicing in rSlo interact to produce BKCa channels with a physiologically relevant phenotype.