title: Modulation of ischaemic contracture in mouse hearts: a 'supraphysiological' response to adenosine.
abstract: While inhibition of ischaemic contracture was one of the first documented cardioprotective actions of exogenously applied adenosine, it is not known whether this is a normal function of endogenous adenosine generated during ischaemic stress. Additionally, the relevance of delayed contracture to postischaemic outcome is unclear. We tested the ability of endogenous versus exogenous adenosine to modify contracture (and postischaemic outcomes) in C57/Bl6 mouse hearts. During ischaemia, untreated hearts developed peak contracture (PC) of 85 +/- 5 mmHg at 8.9 +/- 0.8 min, with time to reach 20 mmHg (time to onset of contracture; TOC) of 4.4 +/- 0.3 min. Adenosine (50 microm) delayed TOC to 6.7 +/- 0.6 min, as did pretreatment with 10 microm 2-chloroadenosine (7.2 +/- 0.5 min) or 50 nm of A(1) adenosine receptor (AR) agonist N(6)-cyclohexyladenosine (CHA) (6.7 +/- 0.3 min), but not A(2A)AR or A(3)AR agonists (20 nm 2-[4-(2-carboxyethyl) phenethylamino]-5' N-methylcarboxamidoadenosine (CGS21680) or 150 nm 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (Cl-IB-MECA), respectively). Adenosinergic contracture inhibition was eliminated by A(1)AR gene knockout (KO), mimicked by A(1)AR overexpression, and was associated with preservation of myocardial [ATP]. This adenosine-mediated inhibition of contracture was, however, only evident after prolonged (10 or 15 min) and not brief (3 min) pretreatment. Ischaemic contracture was also insensitive to endogenously generated adenosine, since A(1)AR KO, and non-selective and A(1)AR-selective antagonists (50 microm 8-sulphophenyltheophylline and 150 nm 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX), respectively), all failed to alter intrinsic contracture development. Finally, delayed contracture with A(1)AR agonism/overexpression or ischaemic 2,3-butanedione monoxime (BDM; 5 microm to target Ca(2+) cross-bridge formation) was linked to enhanced postischaemic outcomes. In summary, adenosinergic inhibition of contracture is solely A(1)AR mediated; the response is 'supraphysiological', evident only with significant periods of pre-ischaemic AR agonism (or increased A(1)AR density); and ischaemic contracture appears insensitive to locally generated adenosine, potentially owing to the rapidity of contracture development versus the finite time necessary for expression of AR-mediated cardioprotection.
authors.affiliation: Heart Foundation Research Centre, Griffith University, Southport, QLD 4217, Australia. j.headrick@griffith.edu.au
authors.forename: Melissa E
authors.initials: ME
authors.lastname: Reichelt
authors.forename: Laura
authors.initials: L
authors.lastname: Willems
authors.forename: Jason N
authors.initials: JN
authors.lastname: Peart
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Ashton
authors.forename: G Paul
authors.initials: GP
authors.lastname: Matherne
authors.forename: Michael R
authors.initials: MR
authors.lastname: Blackburn
authors.forename: John P
authors.initials: JP
authors.lastname: Headrick
mesh_terms: D015762:2-Chloroadenosine / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000241:Adenosine / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009200:Myocardial Contraction; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000503:physiopathology*; D043682:Receptor, Adenosine A1 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D013997:Time Factors; D016277:Ventricular Function, Left / Q000187:drug effects; D017725:Ventricular Pressure / Q000187:drug effects; D014970:Xanthines / Q000494:pharmacology
chemical_list: D043682:Receptor, Adenosine A1; D014970:Xanthines; D015762:2-Chloroadenosine; C010192:9-(2-hydroxy-3-nonyl)adenine; C031433:8-(4-sulfophenyl)theophylline; C051360:1,3-dipropyl-8-cyclopentylxanthine; D013806:Theophylline; D000225:Adenine; D000241:Adenosine