The quest for endothelial atypical cannabinoid receptor: BKCa channels act as cellular sensors for cannabinoids in in vitro and in situ endothelial cells.

Endothelium-dependent component of cannabinoid-induced vasodilation has been postulated to require G-protein-coupled non-CB₁/CB₂ endothelial cannabinoid (eCB) receptor. GPR18 was proposed as a candidate for eCBR. To address the hypothesis that the effects attributed to eCBR are mediated by G-protein-coupled receptor (GPCR)-independent targets, we studied the electrical responses in endothelial cells, focusing on BK_Ca channels. In patches excised from endothelial-derived EA.hy926 cells, N-arachydonoyl glycine (NAGly) and abnormal cannabidiol (abn-cbd), prototypical agonists for eCB receptor, stimulate single BK_Ca activity in a concentration- and Ca²⁺-dependent manner. The postulated eCB receptor inhibitors rimonabant and AM251 were found to inhibit basal and stimulated by NAGly- and abn-cbd BK_Ca activity in cell-free patches. In isolated mice aortas, abn-cbd and NAGly produced endothelial cell hyperpolarization that was sensitive to paxilline, a selective BK_Ca inhibitor, but not to GPR18 antibody, and mimicked by NS1619, a direct BK_Ca opener. In excised patches from mice aortic endothelium, single channel activity with characteristics similar to BK_Ca was established by the addition of abn-cbd and NAGly. We conclude that the two cannabinoids abn-cbd and NAGly initiate a GPR18-independent activation of BK_Ca channels in mice aortic endothelial cells that might contribute to vasodilation to cannabinoids.