Localization and modulation of {alpha}1D (Cav1.3) L-type Ca channel by protein kinase A

Veterans Affairs New York Harbor Healthcare System, State University of New York Downstate Medical Center, Brooklyn and New York School of Medicine, New York, New York Submitted 7 October 2004 ; accepted in final form 19 December 2004 1D L-type Ca channel was assumed to be of neuroendocrine origin only; however, 1D L-type Ca channel knockout mice exhibit sinus bradycardia and atrioventricular block, indicating a distinct role of 1D in the heart. The presence and distribution of 1D Ca channel in the heart and its regulation by protein kinase A (PKA) are just emerging. Our objective was to examine the localization of 1D L-type Ca channel in rabbit and rat hearts and its modulation by PKA. Here, we show the exclusive presence of 1D Ca channel transcript in the sinoatrial node, atrioventricular node, and atria but not in the ventricle by RT-PCR and the expression of 1D Ca channel protein in atrial myocytes' sarcolemma by indirect immunostaining and Western blot. There is no significant difference in the expression level of 1D Ca channel in the left versus right atrium. Superfusion of membrane-permeable 8-bromo-cAMP resulted in a significant increase of the peak current density of 1D Ca current expressed in tsA201 cells. This increase was inhibited by the PKA inhibitor (PKI). Application of 8-bromo-cAMP also readily phosphorylated the 1D Ca channel protein. The results are first to demonstrate that PKA phosphorylation of L-type Ca channel 1D -subunit resulted in an increase of the 1D Ca channel activity. Together with the observation that 1D Ca channel is exclusively present in the sinoatrial node and atria, the findings suggest that 1D Ca channel plays a unique role in the sinoatrial tissue and is a target for sympathetic control of heart rhythm. phosphorylation; protein kinase A; sinoatrial node Address for reprint requests and other correspondence: M. Boutjdir, Research and Development (151A), VA New York Harbor Healthcare System, 800 Poly Place, Brooklyn, NY 11209 (E-mail: mohamed.boutjdir{at}med.va.gov )