The calcium-dependent activity of large-conductance, calcium-activated K+ channels is enhanced by Pyk2- and Hck-induced tyrosine phosphorylation.

Recent results showing that large-conductance, calcium-activated K(+) (BK(Ca)) channels undergo direct tyrosine phosphorylation in the presence of c-Src tyrosine kinase have suggested the involvement of these channels in Src-mediated signaling pathways. Given the important role for c-Src in integrin-mediated signal transduction, we have examined the potential regulation of BK(Ca) channels by proline-rich tyrosine kinase 2 (Pyk2), a calcium-sensitive tyrosine kinase activated upon integrin stimulation. Transient coexpression of murine BK(Ca) channels with either wild-type Pyk2 or hematopoietic cell kinase (Hck), a Src-family kinase, led to an enhancement of BK(Ca) channel activity over the range of 1-10 microM free calcium, whereas coexpression with catalytically inactive forms of either kinase did not significantly alter BK(Ca) gating compared with channels expressed alone. In the presence of either wild-type Pyk2 or Hck, BK(Ca) alpha-subunits were found to undergo tyrosine phosphorylation, as determined by immunoprecipitation and Western blotting strategies. However, tyrosine phosphorylation of the BK(Ca) alpha-subunit was not detected for channels expressed alone or together with inactive forms of either Pyk2 or Hck. Interestingly, wild-type, but not inactive, Pyk2 was also present in BK(Ca) channel immunoprecipitates, suggesting that Pyk2 may coassociate with the BK(Ca) channel complex after phosphorylation. Collectively, the observed modulation and phosphorylation of BK(Ca) channels by Pyk2 and a Src-family kinase may reflect a general cellular mechanism by which G protein-coupled receptor and/or integrin activation leads to the regulation of membrane ion channels.