Endothelium‐mediated contraction by A3 adenosine receptor agonist and its relationship to COX‐1/COX‐2 in A3KO mouse aorta

Abstract

We investigated whether A3 adenosine receptor (A3AR) is involved in endothelium mediated contraction through COX-1/COX-2 pathway leading to contraction in mouse aorta. Organ bath set up was used to study vascular reactivity to various agonists. Mouse aorta with intact endothelium (+E) showed a concentration-dependent contraction to A3AR agonist, Cl-IBMECA (EC50: 2.9×10-9M) in WT and was insignificant in A3KO. At 10-7M, contractions produced by Cl-IBMECA were 29±2.3% (p<0.05) and 6±0.8%, respectively in WT and A3KO (+E) aorta which were abolished in endothelium denuded tissues (−E). A3AR expression (RT-PCR) was reduced by 75% (p<0.05) in (−E) compared with (+E) WT aorta while undetected in A3KO. MRS 1523 (10-6M, A3AR antagonist) inhibited Cl-IBMECA-induced contraction in WT (+E) aorta only while having no effect on CCPA (A1AR agonist)-induced contraction in WT and A3KO. Indomethacin, SC-560 (COX-1 blocker, 10-8M) and NS-398 COX-2 blocker, 10-5M) inhibited Cl-IBMECA-induced contraction in (+E) aorta of WT by 65%, 62% and 14% (p<0.05), respectively and negligible effects in A3KO. Western blot data showed that SC-560 inhibited COX-1 by 63% and 4% while NS-398 inhibited COX-2 by 11% and 2% respectively in WT and A3KO (+E) compared to Cl-IBMECA alone. These data suggest that COX-1 plays a major role in A3AR mediated endothelium-dependent contraction. Supported by grants HL-027339 and HL071802