Melatonin potentiates phenylephrine-stimulated intracellular Ca2+ transient in smooth muscle cell of large arteries of chick embryo.
In the current study we first characterized the properties of the 2-[125I]iodomelatonin binding in pulmonary artery and aorta of chick embryo, and then determined the location of the binding site with autoradiography. Receptor binding assays were used using 2-[125I]iodomelatonin as ligand. The binding was stable, saturable, specific and reversible. Scatchard anlaysis revealed an equilibrium binding constant (Kd) of 27.12 +/- 1.34 pM and a maximum binding capacity (Bmax) of 1.93 +/- 0.19 fmol/mg protein (n = 5). Guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) increased the Kd, but reduced the Bmax, indicating the binding being coupled to a G-protein. Autoradiography revealed the binding sites in the smooth muscle layer. To delineate the physiological function of melatonin in the large artery of the chick embryo, we determined the intracellular calcium ([Ca2+]i) in smooth muscle cells of the aorta with spectrofluorometry, using fura 2-AM as calcium indicator. Melatonin at 10(-8) to 10(-5), which itself had no effect, potentiated the stimulating effect of 0.1 microM phenylephrine, a selective agonist of alpha -adrenoceptor, on [Ca2+]i. In conclusion, specific binding of 2-[125I]iodomelatonin and physiological response to melatonin suggest the existence of melatonin receptor in the smooth muscle of large arteries of the chick embryo. Melatonin potentiates the effects of alpha1-adrenergic stimulation.
Department of Physiology, University of Hong Kong, SAR, China.
Xiao Fei
XF
Wang
Celia Sook-Fun
CS
Pang
Shiu Fun
SF
Pang
Tak Ming
TM
Wong
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo / Q000098:blood supply*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008550:Melatonin / Q000378:metabolism / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology*; D011651:Pulmonary Artery / Q000187:drug effects / Q000378:metabolism*
D010656:Phenylephrine; D008550:Melatonin; D002118:Calcium