Functional regulation of L-type calcium channels via protein kinase A-mediated phosphorylation of the beta(2) subunit

Activation of protein kinase A (PKA) through the beta-adrenergic receptor p athway is crucial for the positive regulation of cardiac L-type currents; h owever it is still. unclear which phosphorylation events cause the robust r egulation of channel function. In order to study whether or not the recentl y identified PKA phosphorylation sites on the beta(2) subunit are of functi onal significance, we coexpressed wild-type (WT) or mutant beta(2) subunits in tsA-201 cells together with an alpha(1C) subunit, alpha(1C)Delta 1905, that lacked the C-terminal 265 amino acids, including the only identified P KA site at Ser-1928. This truncated or,, subunit was similar to the truncat ed alpha(1C) subunit isolated from cardiac tissue not only in size (similar to 190 kDa), but also with respect to its failure to serve as a PKA substr ate. In cells transfected with the WT beta(2) subunit, voltage-activated Ba 2+ currents were significantly increased when purified PKA was included in the patch pipette, Furthermore, mutations of Ser-478 and Ser-479 to Ala, bu t not Ser-459 to Ala, on the beta(2) subunit, completely abolished the PKA- induced increase of currents, The data indicate that the PKA-mediated stimu lation of cardiac L-type Ca2+ currents may be at least partially caused by phosphorylation of the beta(2) subunit at Ser-478 and Ser-479.