title: A(2A) adenosine receptor mediated potassium channel activation in rat epididymal smooth muscle.
abstract: The effects of A(2) adenosine receptor agonists upon phenylephrine-stimulated contractility in preparations of rat epididymis were investigated. Preparations responded to phenylephrine (3 microM) with submaximal contractions. Adenosine and the stable agonists 5'-N-ethylcarboxamido-adenosine (NECA) and 2-p-(2-carboxyethyl) phenethylamino-N-ethylcarboxamide adenosine (CGS 21680) inhibited phenylephrine-induced contractions (potency order, NECA>CGS 21680>adenosine). The A(2A) receptor-selective antagonist, 4-(2-[7-amino-2-(2-furyl)[1,2,4]-triazolo-[2,3-a][1,3, 5]triazin-5-ylamino]ethyl)phenol (ZM 241385, 30 microM) blocked the response to NECA. The A(2A) adenosine receptor-mediated inhibitory responses to NECA were reduced by the K(ATP) channel blocker, glibenclamide (3 microM) and abolished by charybdotoxin (100 nM). The diterpene forskolin elicited a concentration-dependent inhibition of phenylephrine (3 microM)-stimulated contractility (by 62+/-8% of control at 100 microM). Charybdotoxin (100 nM), but not glibenclamide (3 microM) blocked the forskolin (10 microM) inhibition of phenylephrine-stimulated contractility. NECA elicited concentration-dependent increases in both cyclic AMP and cyclic GMP accumulation which were antagonized by ZM 241385 (30 nM). The protein kinase G activator, APT-cyclic GMP (8-(-Aminophenylthio) guanosine-3',5'-cyclic monophosphate) and the protein kinase A activator (Sp)-8-bromoadenosine-3',5'-cyclic monophosphorothioate (Sp-8-Br-cyclic AMPs), inhibited phenylephrine (3 microM) induced contractions of rat epididymis. Glibenclamide (3 microM), but not charybdotoxin (100 nM), inhibited ATP-cyclic GMP responses. Charybdotoxin (100 nM), but not glibenclamide (3 microM) reduced the effect of Sp-8-Br-cyclic AMPs. This study shows that the A(2A) adenosine receptor inhibition of epididymal contractility may be mediated through the activation of charybdotoxin- and glibenclamide-sensitive potassium channels and may involve the activation of both protein kinases A and G.
authors.affiliation: Prince Henry's Institute of Medical Research, PO Box 5152, Clayton 3168, Victoria, Australia. jm.haynes@rmit.edu.au
authors.forename: J M
authors.initials: JM
authors.lastname: Haynes
mesh_terms: D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D006152:Cyclic GMP / Q000502:physiology; D003981:Diazoxide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004822:Epididymis / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015221:Potassium Channels / Q000819:agonists*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D005576:Colforsin; D010656:Phenylephrine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D006152:Cyclic GMP; D003981:Diazoxide