Evidence for the presence of GPRC6A receptors in rat mesenteric arteries

In this study, the presence of GPRC6A receptors in rat mesenteric artery was investigated. In artery homogenates, GPRC6A mRNA was detected and Western blotting showed the presence of GPRC6A protein. Immunohistochemical studies revealed GPRC6A in both endothelial cells and myocytes. In whole vessel segments, the GPRC6A activators, 300 mu M L-ornithine and 100 mu M Al3+, induced endothelium-dependent myocyte hyperpolarizations sensitive to 100 mu M TRAM-34, a blocker of intermediate conductance, Ca2+-sensitive K+ channels (IKCa). Activation of IKCa with calindol (300 nM; a positive allosteric Ca2+-sensing receptor - CaR - modulator) was inhibited by 500 nM ouabain (inhibition of rat type 2 and type 3 Na+/K+-ATPases) but unaffected by 30 mu M Ba2+ (blockade of inwardly rectifying K+ channels). Neither L-ornithine nor Al3+ activated CaRs heterologously expressed in CHO or HEK293 cells. In the presence of 300 mu M L-ornithine or 100 mu M Al3+, myocyte hyperpolarizations to calindol were potentiated whereas this potentiation and hyperpolarizations to L-ornithine were lost following incubation with an anti-GPRC6A antibody. It is concluded that GPRC6A receptors are present on mesenteric artery endothelial cells and myocytes and that their activation selectively opens IKCa channels. This triggers a ouabain-sensitive myocyte hyperpolarization suggesting a close functional relationship between GPRC6A, the IKCa channel and type 2 and/or type 3 Na+/K+-ATPases. (C) 2007 Elsevier Ltd. All rights reserved.