title: Synthetic atrial peptide inhibits intracellular calcium release in smooth muscle.
abstract: The effects of a synthetic atrial peptide (atriopeptin II; AP II) on the agonist-induced intracellular Ca2+ release was examined in the isolated rabbit aorta. The agonist-induced phasic contraction in a Ca2+-free physiological salt solution containing 2 mM ethyleneglycol-bis(beta-aminoethyl-ether)-N,N'-tetraacetic acid (EGTA-PSS) was used as an indicator of the intracellular Ca2+ release. The addition of AP II (10(-9)-10(-7) M) for 15 min to the tissue during the EGTA-PSS exposure caused a dose-dependent inhibition of norepinephrine (NE; 10(-6) M)-induced phasic contraction. The half-maximal inhibiting concentration of AP II was 3 X 10(-9) M, with 10(-7) M AP II causing 91% inhibition. This was confirmed by studying the inhibitory effect of AP II (10(-7) M) on NE-stimulated 45Ca efflux. Furthermore, the internal Ca2+ release by histamine (10(-5) M) and caffeine (25 mM), both of which share this internal Ca2+ pool with NE, was also inhibited by AP II. Thus AP II appears to be a potent inhibitor of the intracellular Ca2+ release that is utilized by various agonists for the activation of vascular smooth muscle. This may be an important mechanism by which AP II produces relaxation of blood vessels.
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D011817:Rabbits
chemical_list: D002110:Caffeine; D006632:Histamine; D009320:Atrial Natriuretic Factor; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine