Involvement of p38-mitogen-activated protein kinase in adenosine receptor-mediated relaxation of coronary artery

The purpose of this study was to explore the involvement of adenosine receptor(s) in porcine coronary artery (PCA) relaxation and to define the role of MAPK signaling pathways. Isometric tensions were recorded in denuded PCA rings. 5'-(N-ethylcarboxamido)adenosine (NECA), a nonselective adenosine receptor agonist, induced a concentration-dependent relaxation (EC50 = 16.8 nM) of PGF(2 alpha) (10 mu M)-preconstricted arterial rings. NECA-induced relaxation was completely blocked by 0.1 mu M SCH-58261 (A(2A) antagonist) at lower doses (1-40 nM) but not at higher doses (80-1,000 nM). MRS-1706 (1 mu M, A(2B) antagonist) was able to shift the NECA concentration-response curve to the right. CGS-21680 (selective A(2A) agonist) induced responses similarly to NECA, whereas N-6-cyclopentyladenosine (A(1) agonist) and Cl-IB-MECA (A(3) agonist) did not. Furthermore, the effect of NECA was attenuated by the addition of SB-203580 (10 mu M, p38 MAPK inhibitor) but not by PD-98059 (10 mu M, MEK inhibitor). Interestingly, SB-203580 had no effect on CGS-21680-induced relaxation. Western blot analysis demonstrated that PGF(2 alpha) and adenosine agonists stimulated p38 MAPK at a concentration of 40 nM in PCA smooth muscle cells. MRS-1706 (1 mu M) significantly reduced NECA-induced p38 MAPK phosphorylation. Addition of NECA and SB-203580 alone or in combination inhibited PGF(2 alpha)-induced p38 MAPK. Western blot data were further confirmed by p38 MAPK activity measurement using activating transcription factor-2 assay. Our results suggest that the adenosine receptor subtype involved in causing relaxation of porcine coronary smooth muscle is mainly A(2A) subtype, although A(2B) also may play a role, possibly through p38 MAPK pathway.