ADENOSINE A(1) RECEPTOR AND ITS GENE-EXPRESSION IN VENTRICLES FROM SPONTANEOUSLY HYPERTENSIVE RATS

We characterized the adenosine A(1) receptor and the levels of its mRN A expression in the ventricles of 6- and 13-wk-old Wistar-Kyoto rats ( WKY) and spontaneously hypertensive rats (SHR). The binding of 2-chlor o-[H-3]cyclopentyladenosine ([H-3]CCPA), an A(1) agonist ligand, to ve ntricular membranes was saturable and reversible. The receptor density was significantly lower in SHR than in WKY at 13 wk. The dissociation constant values were not different among these groups. In Northern bl ot analysis using rat A(1) receptor cDNA, levels of mRNA did not diffe r significantly in the two groups at 13 wk, but the level in SHR signi ficantly exceeded that in WKY at 6 wk. Because plasma adenosine levels were reported to be increased at 13 wk in SHR and we found mRNA level s were similar at this age, the discrepancy between A(1) receptor dens ity and its mRNA levels might be related to the desensitization of A(1 ) receptors. Although the implication of this decreased density of A(1 ) receptors is not known, it may involve an increased susceptibility t o ischemia.