Abstract 15904: Molecular Site of Regulation of Cardiac Cav1.2 Channels in the Fight-or-Flight Response
L-type calcium (Ca) currents conducted by Cav1.2 channels initiate excitation-contraction coupling, and their activity is increased by β-adrenergic/cAMP signaling via phosphorylation by cAMP-dependent protein kinase (PKA). The C-terminus of Cav1.2 is proteolytically processed in vivo near its center, and the distal C-terminal domain (dCT) binds noncovalently to the proximal C-terminus (pCT) and is a potent autoinhibitor. In transfected nonmuscle cells, the autoinhibited Cav1.2 complex plus A Kinase Anchoring Protein 15 is sufficient for regulation of basal and stimulated Cav1.2 activity by phosphorylation of Ser1700 and Thr1704 at the interface between dCT and pCT. Phosphorylation of both residues controls basal Cav1.2 activity, whereas phosphorylation of Ser1700 is required for β-adrenergic stimulation. Mutation of both residues to Ala in mice (STAA) causes 30% reduction in distance run on a treadmill to avoid a mild footshock (WT, 495±39 m; STAA, 329±29 m), indicating impaired exercise tolerance. Cardiac hypertrophy is evident by 3-months of age (WT, 4.2±0.2 mg heart/g; STAA, 5.4±0.4 mg/g). Ventricular myocytes from both neonatal (not shown) and young adult STAA mice have strikingly reduced basal L-type Ca currents (WT, 7.5±0.5 pA/pF; STAA, 2.5±0.2 pA/pF), in part due to decreased expression of Cav1.2 channels. The incremental increase in L-type Ca current by isoproterenol is markedly reduced (3 nM: WT, 1.9-fold; STAA, 1.2-fold. 10 nM: WT, 2.3-fold; STAA, 1.6-fold). Maximal increases in Ca current in saturating isoproterenol (100 nM) are also significantly reduced in STAA myocytes. We conclude that phosphorylation of Ser1700 and Thr1704 is essential for physiological regulation of basal activity of Cav1.2 channels and for up-regulation by the β-adrenergic signaling pathway in vivo. Disruption of phosphorylation at those two sites leads to impaired cardiac function in the whole animal and results in cardiac hypertrophy.
- © 2013 by American Heart Association, Inc.