Desensitization of endothelial P2Y1 receptors by PKC-dependent mechanisms in pressurized rat small mesenteric arteries

Background and purpose: Extracellular nucleotides play a crucial role in the regulation of vascular tone and blood flow. Stimulation of endothelial cell P2Y1 receptors evokes concentration-dependent full dilatation of resistance arteries. However, this GPCR can desensitize upon prolonged exposure to the agonist. Our aim was to determine the extent and nature of P2Y1 desensitization in isolated and pressurized rat small mesenteric arteries. Experimental approach: The non-hydrolyzable selective P2Y1 agonist ADP beta S (3 mu M) was perfused through the lumen of arteries pressurized to 70 mmHg. Changes in arterial diameter and endothelial cell [Ca2+](i) were obtained in the presence and absence of inhibitors of protein kinase C (PKC). Key results: ADP beta S evoked rapid dilatation to the maximum arterial diameter but faded over time to a much-reduced plateau closer to 35% dilatation. This appeared to be due to desensitization of the P2Y1 receptor, as subsequent endothelium-dependent dilatation to acetylcholine (1 mu M) remained unaffected. Luminal treatment with the PKC inhibitors BIS-I (1 mu M) or BIS-VIII (1 mu M) tended to augment concentration-dependent dilatation to ADP beta S (0.1-3 mu M) and prevented desensitization. Another PKC inhibitor, Go 6976 (1 mu M), was less effective in preventing desensitization. Measurements of endothelial cell [Ca2+](i) in pressurized arteries confirmed the P2Y1 receptor but not M-3 muscarinic receptor desensitization. Conclusions and implications: These data demonstrate for the first time the involvement of PKC in the desensitization of endothelial P2Y1 receptors in pressurized rat mesenteric arteries, which may have important implications in the control of blood flow by circulating nucleotides.