Identification of a 15-kDa cAMP-dependent protein kinase-anchoring protein associated with skeletal muscle L-type calcium channels

Voltage-dependent potentiation of skeletal muscle L-type calcium channels requires phosphorylation by cAMP-dependent protein kinase (PKA) that is localized by binding to a cAMP-dependent protein kinase-anchoring protein (AKAP), L-type calcium channels purified from rabbit skeletal muscle contain an endogenous co-purifying protein kinase activity that phosphorylates the alpha 1 and beta subunits of the channel, The co-purifying kinase also phosphorylates a known PKA peptide substrate, is stimulated by cAMP, and is inhibited by PKA inhibitor peptide-(5-24), indicating that it is PKA, PKA activity co-immunoprecipitates with the calcium channel, suggesting that the channel and the kinase are physically associated, Using biotinylated type II regulatory subunit of PKA (RII) as a probe, we have identified a 15-kDa RII binding protein in purified calcium channel preparations, which we have designated AKAP-15. Anti-peptide antibodies directed against the alpha 1 subunit of the calcium channel co-immunoprecipitate AKAP-15. Together, these findings demonstrate a physical link between PKA and the calcium channel and suggest that AKAP-15 may mediate their interaction.