CNGA2 channels mediate adenosine-induced Ca2+ influx in vascular endothelial cells

Abstract

OBJECTIVES - Adenosine is a cAMP-elevating vasodilator that induces both endothelium-dependent and -independent vasorelaxation. An increase in cytosolic Ca ([Ca]i) is a crucial early signal in the endothelium-dependent relaxation elicited by adenosine. This study explored the molecular identity of channels that mediate adenosine-induced Ca influx in vascular endothelial cells. METHODS AND RESULTS - Adenosine-induced Ca influx was markedly reduced by L-cis-diltiazem and LY-83583, two selective inhibitors for cyclic nucleotide-gated (CNG) channels, in H5V endothelial cells and primary cultured bovine aortic endothelial cells (BAECs). The Ca influx was also inhibited by 2 adenylyl cyclase inhibitors MDL-12330A and SQ-22536, and by 2 A2B receptor inhibitors MRS-1754 and 8-SPT, but not by an A2A receptor inhibitor SCH-58261 or a guanylyl cyclase inhibitor ODQ. Patch clamp experiments recorded an adenosine-induced current that could be inhibited by L-cis-diltiazem and LY-83583. A CNGA2-specific siRNA markedly decreased the Ca influx and the cation current in H5V cells. Furthermore, L-cis-diltiazem inhibited the endothelial Ca influx in mouse aortic strips, and it also reduced 5-N- ethylcarboxamidoadenosine (NECA, an A2 adenosine receptor agonist)-induced vasorelaxation. CONCLUSION - CNGA2 channels play a key role in adenosine-induced endothelial Ca influx and vasorelaxation. It is likely that adenosine acts through A2B receptors and adenylyl cyclases to stimulate CNGA2. © 2008 American Heart Association, Inc.