SPECIES COMPARISON OF ADENOSINE AND BETA-ADRENOCEPTORS IN MAMMALIAN ATRIAL AND VENTRICULAR MYOCARDIUM (VOL 246, PG 105, 1993)

The antagonist radioligand 1,3-[H-3]dipropyl-8-cyclopentylxanthine ([H -3]DPCPX) was used to characterize adenosine A(1) receptors in membran e preparations from atrial and ventricular myocardium of rat, rabbit a nd guinea pig. K-d values in crude membranes from guinea pig atria and ventricles (3.3 and 3.0 nM) were higher than those in the other speci es (ranges, 1.5-1.8) and 1.5-1.9 nM). B-max values were greater in atr ia than in ventricles in all four species, and in atria and ventricles of guinea pig (76 and 34 fmol/mg), than in species (ranges, 15-17 and undetectable to 12 fmol/mg). In contrast, guinea pig K-d and B-max va lues for beta-adrenoceptors, which were labelled with (-)-3-[I-125]iod ocyanopindolol, fell within the range of values for the other three ma mmalian species. In semipurified membrane preparations from pig, [H-3] DPCPX and the agonist radioligand [I-125]N-6-4-aminobenzyladenosine ap peared to label a similar population of receptors and gave comparable K-d values in atria (0.73 and 0.66 nM) and in ventricles (0.57 and 0.7 0 nM). In semipurified preparations from pig, the agonist R-(-)-N-6-(2 -phenylisopropyl)adenosine (R-PIA) displaced [H-3]DPCPX in a manner co nsistent with the presence of both high- and low-affinity adenosine A( 1) receptors. The data from this study indicate that the density of ad enosine A(1) receptors in atria is greater than in ventricles, but sim ilar K-d values suggest that the A(1) receptor population is the same in the two cardiac tissues. Also, the data demonstrate that the [H-3]D PCPX antagonist binding characteristics of guinea pig myocardium diffe r from those in rat, rabbit and pig.