Diadenosine Polyphosphates Are Largely Ineffective as Agonists at Natively Expressed P2Y1 and P2Y2 Receptors on Cultured Human Saphenous Vein Endothelial Cells

Abstract

The diadenosine polyphosphates are a group of long-lasting compounds, released into the bloodstream by platelet degranulation. They mediate endothelium-dependent vasodilatation in several animal vascular systems via P2Y receptors coupled to increases in cytoplasmic calcium ([Ca²⁺]_c). However, there is little evidence of diadenosine-mediated vasodilatation in the human vasculature, and a direct interaction with natively expressed P2Y receptors on human endothelium has not been demonstrated. We have therefore studied the effects of diadenosines on primary cultures of human saphenous vein endothelial cells (HSVECs) and related this to the expression of P2Y receptors. HSVECs were loaded with the calcium-sensitive dye fura-2, and nucleotide-stimulated [Ca²⁺]_c responses were recorded. HSVECs responded to 10 µM UTP, ATP and 2-methylthio-ATP but not to UDP. Consistent with the recorded [Ca²⁺]_c responses, RT-PCR analysis of HSVEC RNA amplified specific products for the P2Y₁ and P2Y₂ receptors but not the P2Y₄ and P2Y₆ receptors. HSVECs responded to Ap₃A with a rise in [Ca²⁺]_c, but none of the other diadenosines tested elicited a response. Therefore natively expressed human P2Y₁ and P2Y₂ receptors are insensitive to diadenosine polyphosphates with the exception of Ap₃A. We would therefore predict that the diadenosine polyphosphates have only a limited vasodilatory role in human saphenous veins.