Reichelt Melissa E, Willems Laura, Peart Jason N, Ashton Kevin J, Matherne G Paul, Blackburn Michael R, Headrick John P
Heart Foundation Research Centre, Griffith University, Southport, QLD 4217, Australia.
Exp Physiol. 2007 Jan;92(1):175-85. doi: 10.1113/expphysiol.2006.035568. Epub 2006 Nov 10.
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.
虽然抑制缺血性挛缩是外源性应用腺苷最早被记录的心脏保护作用之一，但尚不清楚这是否是缺血应激期间内源性腺苷的正常功能。此外，延迟性挛缩与缺血后结局的相关性尚不清楚。我们测试了内源性与外源性腺苷在C57/Bl6小鼠心脏中改变挛缩（以及缺血后结局）的能力。在缺血期间，未经处理的心脏在8.9±0.8分钟时出现85±5 mmHg的峰值挛缩（PC），达到20 mmHg的时间（挛缩开始时间；TOC）为4.4±0.3分钟。腺苷（50 μmol）将TOC延迟至6.7±0.6分钟，10 μmol 2-氯腺苷预处理（7.2±0.5分钟）或50 nM A1腺苷受体（AR）激动剂N6-环己基腺苷（CHA）（6.7±0.3分钟）也有同样效果，但A2AAR或A3AR激动剂（分别为20 nM 2-[4-(2-羧乙基)苯乙氨基]-5'-N-甲基羧酰胺腺苷（CGS21680）或150 nM 2-氯-N6-(3-碘苄基)-腺苷-5'-N-甲基脲苷（Cl-IB-MECA））则没有。A1AR基因敲除（KO）消除了腺苷能性挛缩抑制，A1AR过表达则模拟了这种抑制，并且与心肌[ATP]的保存有关。然而这种腺苷介导的挛缩抑制仅在长时间（10或15分钟）而非短暂（3分钟）预处理后才明显。缺血性挛缩对内源性生成的腺苷也不敏感，因为A1AR KO以及非选择性和A1AR选择性拮抗剂（分别为50 μmol 8-磺苯基茶碱和150 nM 8-环戊基-1,3-二丙基黄嘌呤（DPCPX））均未能改变内在挛缩的发展。最后，A1AR激动/过表达或缺血性2,3-丁二酮单肟（BDM；5 μmol以靶向Ca2+横桥形成）引起的延迟性挛缩与缺血后结局的改善有关。总之，腺苷能性挛缩抑制仅由A1AR介导；这种反应是“超生理性的”，仅在缺血前AR激动（或A1AR密度增加）的显著时间段才明显；并且缺血性挛缩似乎对局部生成的腺苷不敏感，这可能是由于挛缩发展的快速性与AR介导的心脏保护作用表达所需的有限时间相比。
