Expression and desensitisation of A2 purinoceptors on cultured bovine aortic endothelial cells

Abstract

Purine nucleotides and their metabolites are important mediators of vascular tone. Adenosine promotes relaxation of vascular smooth muscle, acting on the A₂ subclass of purinoceptors. There is some evidence that these receptors are also present on vascular endothelial cells. We have therefore examined cultured aortic endothelial cells for adenosine (A₂) sensitivity. Bovine aortic endothelial cells (AG4762) were obtained from the Institute of Aging cell repository (USA), and cultured in monolayer flasks. Adenylate cyclase activity in homogenates of AG4762 cells was increased by 5′-(N-ethylcarboxamido)-adenosine (NECA) > 2-chloroadenosine > adenosine. NECA dependent activation of adenylate cyclase was inhibited by 3-isobutyl-l-methylxanthine > theophylline > caffeine. The rank order of potency of these compounds identified the responses as mediated by A₂ purinoceptors. Prolonged exposure of AG4762 cells to NECA in culture resulted in loss of A₂ purinoceptor responsiveness, and purinoceptor activity could be restored to non-dividing densensitised cells by further culture in the absence of the desensitising agent. The cyclic AMP dependent phosphorylation of specific sites in endothelial cells may trigger a number of important biological events which are yet to be determined.