Received for publication July 6, 2007.
Revised November 6, 2007.
Accepted for publication November 7, 2007.

A novel actin-binding domain on Slo1 calcium-activated potassium channels is necessary for their expression in the plasma membrane

Abstract

Large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels regulate the physiological properties of many cell types. The gating properties of BK_Ca channels are Ca²⁺-, voltage- and stretch-sensitive, and stretch-sensitive gating of these channels requires interactions with actin microfilaments subjacent to the plasma membrane. However, trafficking of BK_Ca channels to the plasma membrane has been associated with processes that alter cytoskeletal dynamics. Here we show that the Slo1 subunits of BK_Ca channels contain a novel cytoplasmic actin-binding domain (ABD) close to the C-terminal, considerably downstream from regions of the channel molecule that play a major role in determining channel gating properties. Actin binding to the ABD can occur in a binary mixture in the absence of other proteins. Co-expression of a small ABD-GFP fusion protein that competes with full-length Slo1 channels for binding to actin markedly suppresses trafficking of full-length Slo1 channels to the plasma membrane. In addition, Slo1 channels containing deletions of the ABD that eliminate actin binding are retained in intracellular pools and are not expressed on the cell surface. At least one point mutation within the ABD (L1020A) reduces surface expression of Slo1 channels to about 25% of wild-type, but does not cause a marked effect on the gating of point mutant channels that reach the cell surface. These data suggest that Slo1-actin interactions are necessary for normal trafficking of BK_Ca channels to the plasma membrane, and the mechanisms of this interaction may be different from those that underlie F-actin and stretch-sensitive gating.

Key words: Ion channel regulation, Func. analysis receptor/ion channel mutants, Immunocytochemistry, Mutagenesis/Chimeric approaches

This article has been cited by other articles:

				E. Y. Kim, K.-J. Choi, and S. E. Dryer Nephrin binds to the COOH terminus of a large-conductance Ca2+-activated K+ channel isoform and regulates its expression on the cell surface Am J Physiol Renal Physiol, July 1, 2008; 295(1): F235 - F246. [Abstract] [Full Text] [PDF]