ATP RAISES [CA2+](I) VIA DIFFERENT P-2-RECEPTOR SUBTYPES IN FRESHLY ISOLATED AND CULTURED AORTIC MYOCYTES

In vascular smooth muscle, extracellular ATP induces an increase in intracellular [Ca2+] ([Ca2+](i)). Various agonists have been used to characterize P-2-purinoeeptor subtypes involved in the ATP-induced [Ca2+](i) rise, measured by indo 1 fluorescence, in both freshly isolated and cultured rat aortic smooth muscle cells. alpha,beta-Methylene-ATP increased [Ca2+](i) via Ca2+ entry through P-2x-receptor channels in freshly isolated but not in cultured cells. 2-Methylthio-ATP and ADP failed to release Ca2+ via P-2y-receptor activation in freshly isolated cells, whereas such a response was obtained in cultured cells. UTP, by stimulating P-2u receptors, released Ca2+ from intracellular stores in both freshly isolated and cultured cells. These results suggest that, in the course of the culture process, P-2x-receptor activation-induced responses were lost, whereas P-2y-receptor activation-induced [Ca2+](i) rise appeared, these two phenomena being independent. Responses to P-2x-receptor agonist were lost in all culture conditions, whereas functional P-2y receptors appeared only in cells that were stimulated with serum to induce cell cycle progression. The phenotypic modulation of vascular myocytes was therefore associated with a change in the functional P-2-purinoceptor subtypes.