title: Action of adenosine in estrogen-primed nonpregnant guinea pig myometrium: characterization of the smooth muscle receptor and coupling to phosphoinositide metabolism.
abstract: The smooth muscle of guinea pig uterus is contracted by adenosine in a manner consistent with the presence of a purine nucleoside receptor of the P1-A1 subtype that is uncoupled from adenylate cyclase. Here we investigate the signal transduction mechanism responsible for adenosine's ability to contract uterine smooth muscle. The A1 adenosine receptor antagonist [3H]-8-cyclopentyl-1.3- dipropyl xanthine ([3H]CPX) bound reversibly to a large number (172 +/- 25 fmol/mg of protein) of receptors in myometrial smooth muscle membranes from estrogen-primed virgin guinea pigs with an affinity (KD = 1.77 +/- 0.21 nM) similar to that expected of [3H]CPX binding to both central and peripheral A1 receptors. In the absence of the stable GTP analog, guanosine-5'-O-[3-thiotriphosphate], agonist competition of [3H]CPX binding resulted in a biphasic curve that was best fit assuming the presence of equal populations of two affinity states of the receptor. Addition of guanosine-5'-O-[3-thiotriphosphate] (10 microM) resulted in a monophasic competition curve of low affinity suggesting coupling of this A1 receptor to effector via a GTP binding protein. In [3H]myo-inositol labeled strips of myometrial smooth muscle, the adenosine agonist R-phenylisopropyl adenosine (R-PIA) stimulated the rapid formation of inositol-1,4,5-trisphosphate (InsP3) that was antagonized by addition of the nucleoside receptor antagonist 8-sulfophenyl theophylline. Prostaglandin stimulation of myometrial strips also increased InsP3 formation. Furthermore, R-PIA stimulated the disappearance of inositol phosphate (InsP) in a fashion consistent with agonist stimulation of an inositol phosphatase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, University of Nevada School of Medicine, Reno.
authors.forename: W P
authors.initials: WP
authors.lastname: Schiemann
authors.forename: K O
authors.initials: KO
authors.lastname: Doggwiler
authors.forename: I L
authors.initials: IL
authors.lastname: Buxton
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D006168:Guinea Pigs; D007294:Inositol / Q000378:metabolism; D008094:Lithium / Q000494:pharmacology; D009130:Muscle, Smooth / Q000378:metabolism*; D009215:Myometrium / Q000187:drug effects / Q000378:metabolism*; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011453:Prostaglandins / Q000502:physiology; D011983:Receptors, Purinergic / Q000032:analysis*; D014970:Xanthines / Q000378:metabolism
chemical_list: D004967:Estrogens; D010716:Phosphatidylinositols; D011453:Prostaglandins; D011983:Receptors, Purinergic; D014970:Xanthines; D010660:Phenylisopropyladenosine; D007294:Inositol; D008094:Lithium; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000241:Adenosine