title: The effects of atriopeptin II on calcium fluxes in rabbit aorta.
abstract: Effects of atriopeptin II (AP II) at 10(-7) M on the 45Ca flux and contractile responses to vasoconstrictors including norepinephrine (NE), angiotensin II (angio II) and high K were studied in isolated rabbit aortic strips. Augmentation of 45Ca efflux from aorta in normal physiological saline (PSS) due to NE and angio II each at 3 X 10(-7) M was greatly inhibited by AP II, suggesting that stimulated increase in cytosolic Ca2+ was suppressed. In contrast, the 45Ca efflux responses to KCl (20 and 40 mM) were not affected by AP II. Furthermore, the marked inhibition of contractile responses to NE (-58%) and angio II (-57%) by AP II was accompanied by significant decreases in 45Ca influx, whereas AP II exhibited only a modest inhibition on KCl (40 mM)-induced contraction (-28%) without affecting the accompanying increase in 45Ca influx. The 45Ca efflux from aortae in Ca2+-free PSS due to NE was markedly diminished by AP II, suggesting impairment of intracellular Ca2+ release. With tissues in either a basal or post-stimulation state (tissue Ca2+ previously increased with KCl stimulation), AP II did not stimulate 45Ca efflux in Ca2+-free PSS, suggesting its lack of effect on Ca extrusion. It is concluded that AP II is preferentially antagonistic against vascular responses to NE and angio II vs. high K and that inhibition of Ca entry and release forms the primary basis of its potent vasorelaxant action against vasoconstrictors.
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism; D009320:Atrial Natriuretic Factor / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D007473:Ion Channels; D000804:Angiotensin II; D011189:Potassium Chloride; D009320:Atrial Natriuretic Factor; D002118:Calcium; D009638:Norepinephrine