Novel mitogenic effect of adenosine on coronary artery smooth muscle cells -: Role for the A1 adenosine receptor

Adenosine is a vascular endothelial cell mitogen, but anti-mitogenic for aortic smooth muscle cells and fibroblasts when acting via the A(2B) adenosine receptor. However, we show that adenosine increases porcine coronary artery smooth muscle cell (CASMC) number, cellular DNA content, protein synthesis, and PCNA staining. RT-PCR analysis indicates that porcine CASMC express A(1), A(2A), A(3), and barely detectable levels of A(2B) receptor mRNAs. The mitogenic effect of adenosine is mimicked by NECA, CCPA, and R-PIA, but not by CGS21680 and 2-Cl-IB-MECA, and is inhibited by DPCPX, indicating a prominent role for the A(1) receptor. This interpretation is supported by the finding that adenosine- and CCPA-induced DNA synthesis is significantly inhibited by pertussis toxin, but substantially potentiated by PD81723, an allosteric enhancer of the A(1) receptor. When a cDNA encoding the porcine A(1) receptor was cloned and expressed in COS-1 cells, A(1) receptor pharmacology is confirmed. Anti-sense oligonucleotides to the cloned sequence dramatically suppress the mitogenic effect of adenosine and CCPA. Conversely, over-expression of the cloned A(1) receptor in CASMC increases adenosine- and CCPA-induced DNA synthesis. Furthermore, stimulation with adenosine or CCPA of intact coronary arteries in an organ culture model of vascular disease increases cellular DNA synthesis, which was abolished by DPCPX. We conclude that adenosine acts as a novel mitogen in porcine CASMC that express the A(1) adenosine receptor, possibly contributing to the development of coronary artery disease.