Journal of Biological Chemistry
Volume 275, Issue 39, 29 September 2000, Pages 30683-30689
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MECHANISMS OF SIGNAL TRANSDUCTION
Enhanced Activity of a Large Conductance, Calcium-sensitive K+ Channel in the Presence of Src Tyrosine Kinase*

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Large conductance, calcium-sensitive K+ channels (BKCa channels) contribute to the control of membrane potential in a variety of tissues, including smooth muscle, where they act as the target effector for intracellular “calcium sparks” and the endothelium-derived vasodilator nitric oxide. Various signal transduction pathways, including protein phosphorylation can regulate the activity of BKCa channels, along with many other membrane ion channels. In our study, we have examined the regulation of BKCa channels by the cellular Src gene product (c Src), a soluble tyrosine kinase that has been implicated in the regulation of both voltage- and ligand-gated ion channels. Using a heterologous expression system, we observed that co-expression of murine BKCa channel and the human c Src tyrosine kinase in HEK 293 cells led to a calcium-sensitive enhancement of BKCa channel activity in excised membrane patches. In contrast, co-expression with a catalytically inactive c Src mutant produced no change in BKCa channel activity, demonstrating the requirement for a functional c Src molecule. Furthermore, we observed that BKCa channels underwent direct tyrosine phosphorylation in cells co-transfected with BKCa channels and active c Src but not in cells co-transfected with the kinase inactive form of the enzyme. A single Tyr to Phe substitution in the C-terminal half of the channel largely prevented this observed phosphorylation. Given that c Src may become activated by receptor tyrosine kinases or G-protein-coupled receptors, these findings suggest that c Src-dependent tyrosine phosphorylation of BKCa channels in situ may represent a novel regulatory mechanism for altering membrane potential and calcium entry.

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Published, JBC Papers in Press, July 12, 2000, DOI 10.1074/jbc.M004292200

*

This work was supported by an Establishment Grant from the Alberta Heritage Foundation for Medical Research, by funds from the Heart and Stroke Foundation of Alberta/Northwest Territories, and by a Young Investigator Award from the University of Calgary (to A. P. B.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.