Characterization of Beta-Adrenergic Receptor Binding Sites Using ((superscript 3)H) Dihydroalprenolol in Bovine Tracheal Smooth Muscle

以((上標 3)H)Dihydroalprenolol鑒定牛氣管平滑肌之交感神經乙受體結合處

程斌(J. B. Cheng)

《The Chinese Journal of Physiology》 25卷1期 (1982/06) Pp. 7-16

摘要

Tracheal smooth muscle is a target organ for adrenergic stimuli. Activation of its beta-adrenergic receptors in vivo or in vitro generally results in muscle relaxation. To investigate directly the tracheal beta-receptors, I studied the binding of ((superscript 3)H)dihydroalprenolol (DHA) to a crude membrane preparation of bovine tracheal smooth muscle. Binding at 25℃ was rapid and reversible with an association rate constant of 0.0394 nM^(-1) min^(-1) and a dissociation rate constant of 0.0197 min^(-1). Scatchard analysis of equilibrium experiments indicates the presence of a saturable, high-affinity binding site. The concentration of this site was 136.2±55.9 fmol/mg protein and the dissociation constant was 0.73±0.27 nM. (－) Propranolol competed with DHA at this site was 79 times more potent than (+) propranolol, and was about 1000 times for (－) metoprolol, a selective beta1 antagonist. The order of potency for adrenergic agonists to compete for DHA binding was (－) isoproterenol＞(－) epinephrine＞(－) norepinephrine. This order is compatible with beta2-adrenergic interactions. On the other hand, there was no demonstrable specific ((superscript 3)H) dihydroergocryptine, an alpha antagonist, binding site with this preparation. These results indicate that DHA can be used as an experimental tool to study tracheal muscle beta receptors, and suggest that no alpha receptor exists in this tissue.

並列摘要

Tracheal smooth muscle is a target organ for adrenergic stimuli. Activation of its beta-adrenergic receptors in vivo or in vitro generally results in muscle relaxation. To investigate directly the tracheal beta-receptors, I studied the binding of ((superscript 3)H)dihydroalprenolol (DHA) to a crude membrane preparation of bovine tracheal smooth muscle. Binding at 25℃ was rapid and reversible with an association rate constant of 0.0394 nM^(-1) min^(-1) and a dissociation rate constant of 0.0197 min^(-1). Scatchard analysis of equilibrium experiments indicates the presence of a saturable, high-affinity binding site. The concentration of this site was 136.2±55.9 fmol/mg protein and the dissociation constant was 0.73±0.27 nM. (－) Propranolol competed with DHA at this site was 79 times more potent than (+) propranolol, and was about 1000 times for (－) metoprolol, a selective beta1 antagonist. The order of potency for adrenergic agonists to compete for DHA binding was (－) isoproterenol＞(－) epinephrine＞(－) norepinephrine. This order is compatible with beta2-adrenergic interactions. On the other hand, there was no demonstrable specific ((superscript 3)H) dihydroergocryptine, an alpha antagonist, binding site with this preparation. These results indicate that DHA can be used as an experimental tool to study tracheal muscle beta receptors, and suggest that no alpha receptor exists in this tissue.

並列關鍵字

(3H)dihydroalprenolol ； Tracheal Smooth Muscle ； Bate-Adrenergic Receptors