Calcitonin gene related peptide (CGRP) activates adenylate cyclase of bovine aortic endothelial cells: guanosine 5' triphosphate dependence and partial agonist activity of a tyrosinated analogue

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Abstract
Human calcitonin gene related peptide (hCGRP) has been shown to release prostacyclin from cultured human endothelial cells and activate adenylate cyclase in endothelial cell membrane preparations. Human endothelial cells are difficult to obtain, so a bovine aortic endothelial cell model has been used to investigate the actions of hCGRP further. Bovine aortic endothelial cells were cultured and membranes prepared from them. In these membrane fractions there was a concentration dependent activation of adenylate cyclase by hCGRP, which required the presence of guanosine 5′ triphosphate. Basal activity of adenylate cyclase was 41.5 pmol·min−1·mg−1 protein. The concentration for half maximum activation of adenylate cyclase (Kact) by hCGRP was 842 nM. The maximum increase in adenylate cyclase activity above basal in response to hCGRP was 180 pmol cyclic adenosine monophosphate·min−1·mg−1 protein. A [tyr°] substituted analogue of hCGRP ([tyr°]-hCGRP) also activated adenylate cyclase (Kact 2.2 μM) but the maximum stimulation by [tyr°]-hCGRP was less than that obtained with native peptide. The same analogue partially inhibited the hCGRP dependent activation of adenylate cyclase (Ki = 2 μM). These studies show that hCGRP acts on a receptor on endothelial cells to activate adenylate cyclase and that [tyr°]-hCGPO is a partial agonist at this receptor. The potent vasodilator properties of hCGRP may be mediated through or modified by its interaction with endothelial cells.