[H]Nitrendipine Receptors of Porcine Vascular Smooth Muscle: Differences Between Coronary Artery and Aorta

Characteristics of the bindings of [H]( )dihydroalprenolol, [I]( ) iodocyanopindolol, ['H]prazosin, [H]yohimbine, and [H]nltrendiplne to porcine coronary membranes were investigated and the results compared with studies of porcine aortic membranes. In the equilibrium binding study carried out in sarcolemma-enriched fractions, there were no major differences in the Kj values of these radioligands between coronary artery and aorta. However, the densities of /3-, a r , and aradrenoceptors and [H]nitrendipine receptors of coronary artery were 258, 12, 12, and 561 fmol/mg protein, respectively, while those of aorta were 37,525,1,000, and 215 fmol/mg protein. /3-Adrenergic agonists competed with [H]( (dihydroalprenolol binding sites in coronary artery, the order of potency being ( )isoproterenol > ( )norepinephrine > ( )epinephrine > ( + )isoproterenol. In case of aorta, the order was ( )isoproterenol > ( )epinephrine > ( )norepinephrine. The competition by (± )bisoprolol (/^-selective antagonist) and ICI 118,551032-selective antagonist) for [I](-)iodocyanopindolol binding sites in coronary artery resulted in nonlinear Hofstee plots ()3,: /32 = 90%: 10%). In case of aorta, linear Hofstee plots were obtained. From these results, we conclude that (1) coronary /9receptors in pigs are predominately of /3,-type, while those of aorta are of /32-type; (2) regarding the relative population of adrenoceptors, coronary artery is /3-dominant (fi/a = 11), while aorta is adominant (fila = 0.02); (3) compared with a-adrenoceptors, coronary artery has a greater number of [H]nitrendipine binding sites (nitrendipine/a-adrenoceptor = 23) than aorta (nitrendipine/a-adrenoceptor = 0.14). {Circulation Research 1987;60:6:837-844)