Characterisation of responses to PGE2-G in the porcine coronary artery, rat aorta and murine microglial cell line BV-2

Prostaglandin glyceryl esters are derived from cyclooxygenase-2 oxygenation of the endocannabinoid 2-arachidonoylglycerol. Prostaglandin E2 glyceryl ester (PGE2G) may be involved in inflammation but very little else is known about its patho/physiological roles. A recent study identified interaction of PGE2G with P2Y6 receptors in isolated cells. P2Y6 receptors are involved in cardiovascular regulation and UDP is the agonist. In this study, it was investigated whether PGE2G can influence vascular contractility through P2Y6 receptors. Isometric tension recordings were used to evaluate responses of segments of porcine coronary artery (PCA) (stored at 4ºC overnight) and rat thoracic aorta (freshly isolated). In PCA, UDP (1.3×10-6-1.3×10-3 M) and PGE2-G (1.3×10-9-4×10-6 M) produced concentration-dependent contractions which were unaffected by P2Y6 receptor antagonist, MRS 2578. UDP contractions were blocked by P2 receptor antagonist suramin (p<0.001; two-way ANOVA). UDP also acts at P2Y14 and P2Y2 receptors; antagonists PPTN (P2Y14) and AR-C118925XX (P2Y2) failed to alter UDP responses. UDP responses were also characterised in U46619-precontracted PCAs in presence of AR-C 118925XX in which there was no evidence for the presence of relaxant P2Y6 receptors and enhanced PGE2-G responses were produced in endothelium-denuded vessels, pointing out involvement of a smooth muscle coupled receptor in mediating responses. PGE2-G activates EP receptors; nonselective EP antagonist AH-6809 significantly blocked contractile responses evoked by both PGE2-G (p<0.05 at 4×10-6 M) and UDP (p<0.001 at 10-3 M). In rat aorta, UDP (1×10-8-1×10-5M) produced concentration-dependent relaxations (pEC50 6.4 ± 0.1, Rmax 77 ± 8%) which were unaffected by MRS 2578 (pEC50 6.4 ± 0.1, Rmax 80 ± 10% (n=7). PGE2-G (1×10-10-3×10-6M) produced concentration-dependent relaxations (pEC50 value of 8.6 ± 0.2 and Rmax 31 ± 5%) which were also unaffected by MRS 2578 (pEC50 value of 8.6 ± 0.3; Rmax 25 ± 5%, n = 7). UDP also acts at P2Y2 receptors; responses characterised in presence of AR-C 118925XX demonstrated enhanced responses, showing involvement of another P2Y receptor. Endothelium-denuded experiments presented evidence for attenuated UDP responses demonstrating involvement of a receptor coupled to endothelium. Application of the nonselective EP antagonist AH-6809 did not alter PGE2-G evoked relaxations but concentration-dependent contractions evoked at 0.3 μM were abolished (p<0.0001 at 3×10-6 M) and UDP responses (pEC50 value 5.2 ± 1.6 and Rmax of 77 ± 8%) were also enhanced (pEC50 value of 6.7 ± 0.1 and Rmax of 89 ± 13%, p<0.05, n=6). Calcium release evoked by UDP (1×10-4-6×10-9 M) in presence of MRS 2578 was significantly attenuated in P2Y6 expressing BV-2 cells. PGE2-G (1×10-4-6×10-9 M) responses remained unchanged. In summary, UDP and PGE2-G responses appear to behave independently to the P2Y6 receptor in both blood vessels however, UDP mediated calcium release demonstrated involvement of P2Y6 receptors unlike PGE2-G. Evidence points out that PGE2-G responses do not involve activation of P2Y6 receptors but is more potent than UDP at evoking responses. Inhibition by AH-6809 suggests that UDP may be stimulating a P2Y receptor mediated prostanoid release. Overall, the identities of UDP and PGE2-G-sensitive receptors in the blood vessels is yet unclear but it does not involve P2Y2, P2Y6 or P2Y14 receptors. Thus, further molecular targets are being investigated.

Topic: Adenosine and Purinergic Signaling
Subfield: Physiology
Field: Biochemistry, Genetics and Molecular Biology
Domain: Life Sciences