Requirement of the Ca²⁺ channel β₂ subunit for sympathetic PKA phosphorylation

Facilitation of cardiac function in response to signals from the sympathetic nervous system is initiated by the phosphorylation of L-type voltage-dependent Ca²⁺ channels (VDCCs) by protein kinase A (PKA), which in turn is activated by β-adrenoceptors. Among the five subunits (α₁, β, α₂/δ, and γ) of VDCCs, the α₁ subunit and the family of β subunits are substrates for PKA-catalyzed phosphorylation; however, the subunit responsible for β-adrenergic augmentation of Ca²⁺ channel function has yet to be specifically identified. Here we show that the VDCC β₂ subunit is required for PKA phosphorylation upon sympathetic acceleration. In mice with β₂ subunit-null mutations, cardiac muscle contraction in response to isoproterenol was reduced and there was no significant increase in Ca²⁺ channel currents upon PKA-dependent phosphorylation. These findings indicate that within the sympathetic nervous system the β₂ subunit of VDCCs is required for physiological PKA-dependent channel phosphorylation.