Characteristics of adrenoceptors and (/sup 3/H)nitrendipine receptors of porcine vascular smooth muscle: differences between coronary artery and aorta
Characteristics of the bindings of (/sup 3/H)(-)dihydroalprenolol, (/sup 125/I)(-)iodocyanopindolol, (/sup 3/H)prazosin, (/sup 3/H)yohimbine, and (/sup 3/H)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 (/sup 3/H)nitrendipine receptors of coronary artery were 258, 12, 12, and 561 fmol/mg protein, respectively, while those of aorta were 37, 525, 1000, and 215 fmol/mg protein. beta-Adrenergic agonists competed with (/sup 3/H)(-)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 (/sup 125/I)(-)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 (/sup 3/H)nitrendipine binding sites (nitrendipine/alpha-adrenoceptor = 23) than aorta (nitrendipine/alpha-adrenoceptor = 0.14).
- Research Organization:
- Kyushu Univ., Japan
- OSTI ID:
- 6075493
- Journal Information:
- Circ. Res.; (United States), Vol. 60:6
- Country of Publication:
- United States
- Language:
- English
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550201* - Biochemistry- Tracer Techniques