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2[ 125 I]Iodomelatonin binding and interaction with β‐adrenergic signaling in chick heart/coronary artery physiology
Author(s) -
Pang Celia S.,
Xi Si C.,
Brown Gregory M.,
Pang Shiu F.,
Shiu Stephen Y. W.
Publication year - 2002
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1034/j.1600-079x.2002.01860.x
Subject(s) - medicine , endocrinology , receptor , melatonin , pertussis toxin , myocyte , adrenergic receptor , biology , melatonin receptor , chronotropic , g protein , heart rate , blood pressure
2[ 125 I]Iodomelatonin ([ 125 I]Mel) binding sites were characterized on membrane preparations of young chick hearts. [ 125 I]Mel binding was rapid, saturable, stable, reversible, specific and of picomolar affinity and femtomolar density. Guanosine 5′‐ O ‐(3‐thiotriphosphate) significantly lowered the binding affinity by one‐ to twofold, supporting G‐protein linkage of melatonin receptors. Binding was detected as early as embryonic day‐9 (E9), and increased steadily peaking at E13 before it slowly declined to about 15% of the peak level a week posthatch. Specific [ 125 I]Mel binding was significantly increased by in ovo administration of inotropic agents dopamine and isoproterenol. Melatonin or 2‐iodo‐ N ‐butanoyl‐tryptamine inhibited isoproterenol‐stimulated cAMP accumulation in primary heart cell cultures and the effect was attenuated after pretreatment with pertussis toxin (PTX). Localization of melatonin receptors using autoradiography showed intense labeling in the coronary arteries in all age groups whereas those in the myoblasts decreased as the heart matured. While the myoblasts and undifferentiated developing coronary arteries expressed melatonin MT 1 receptor subtype in E11 hearts as detected by immunostaining with anti‐MT 1 receptor serum, immunoreactivities were observed mostly on the endothelium/subendothelium and smooth muscle cells of the well developed coronary vessels in posthatch hearts. Collectively, our data suggest the presence of PTX‐sensitive, G protein‐coupled melatonin receptors, whose expression is up‐regulated by dopamine and isoproterenol, in the chick heart. Activation of these receptors, which include MT 1 subtype, may modulate β‐adrenergic receptor‐mediated cAMP signaling in the control of chick heart and coronary artery physiology.