title: Characteristics of adrenoceptors and [3H]nitrendipine receptors of porcine vascular smooth muscle: differences between coronary artery and aorta.
abstract: Characteristics of the bindings of [3H](-)dihydroalprenolol, [125I](-)iodocyanopindolol, [3H]prazosin, [3H]yohimbine, and [3H]nitrendipine 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 Kd values of these radioligands between coronary artery and aorta. However, the densities of beta-, alpha 1-, and alpha 2-adrenoceptors and [3H]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. beta-Adrenergic agonists competed with [3H](-)dihydroalprenolol binding sites in coronary artery, the order of potency being (-)isoproterenol greater than (-)norepinephrine greater than (-)epinephrine greater than (+)isoproterenol. In case of aorta, the order was (-)isoproterenol greater than (-)epinephrine greater than (-)norepinephrine. The competition by (+/-)bisoprolol (beta 1-selective antagonist) and ICI 118,551 (beta 2-selective antagonist) for [125I](-)iodocyanopindolol binding sites in coronary artery resulted in nonlinear Hofstee plots (beta 1:beta 2 = 90%:10%). In case of aorta, linear Hofstee plots were obtained. From these results, we conclude that coronary beta-receptors in pigs are predominantly of beta 1-type, while those of aorta are of beta 2-type; regarding the relative population of adrenoceptors, coronary artery is beta-dominant (beta/alpha = 11), while aorta is alpha-dominant (beta/alpha = 0.02); compared with alpha-adrenoceptors, coronary artery has a greater number of [3H]nitrendipine binding sites (nitrendipine/alpha-adrenoceptor = 23) than aorta (nitrendipine/alpha-adrenoceptor = 0.14).
mesh_terms: D000818:Animals; D001011:Aorta / Q000378:metabolism; D001665:Binding Sites; D015220:Calcium Channels; D003331:Coronary Vessels / Q000378:metabolism; D004082:Dihydroalprenolol / Q000378:metabolism; D020120:Iodocyanopindolol; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009568:Nitrendipine / Q000378:metabolism; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011224:Prazosin / Q000378:metabolism; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013552:Swine; D014316:Tritium; D015016:Yohimbine / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D011941:Receptors, Adrenergic; D011978:Receptors, Nicotinic; D014316:Tritium; D015016:Yohimbine; D004082:Dihydroalprenolol; D020120:Iodocyanopindolol; D009568:Nitrendipine; D010869:Pindolol; D011224:Prazosin