Cooperative cardioprotection through adenosine A1 and A2A receptor agonism in ischemia-reperfused isolated mouse heart.

Recent reports have shown that adenosine A1 receptor-mediated cardioprotection requires concomitant A2 receptor activation, but no study thus far has shown that this phenomenon occurs using A1 agonists at reperfusion. Thus, we compared adenosine A2A receptor knockout (A2AKO) and wild-type mouse hearts (n = 9-11) subjected to global ischemia (30 minutes) and reperfusion (60 minutes) in the presence and absence of the A1 agonist N-cyclopentlyadenosine (CPA). We also determined the effects of selective antagonists at A2A and A2B receptors on CPA-induced protection.

A novel highly selective adenosine A1 receptor agonist VCP28 reduces ischemia injury in a cardiac cell line and ischemia-reperfusion injury in isolated rat hearts at concentrations that do not affect heart rate.

The cardioprotective effects of a novel adenosine A1 receptor agonist N6-(2,2,5,5-tetramethylpyrrolidin-1-yloxyl-3-ylmethyl) adenosine (VCP28) were compared with the selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) in a H9c2(2-1) cardiac cell line-simulated ischemia (SI) model (12 hours) and a global ischemia (30 minutes) and reperfusion (60 minutes) model in isolated rat heart model. H9c2(2-1) cells were treated with CPA and VCP28 at the start of ischemia for entire ischemic duration, whereas isolated rat hearts were treated at the onset of reperfusion for 15 minutes. In the H9c2(2-1) cells SI model, CPA and VCP28 (100 nM) significantly (P < 0.

Delineating the mode of action of adenosine A1 receptor allosteric modulators.

Despite the identification of 2-amino-3-benzoylthiophenes (2A3BTs) as the first example of small-molecule allosteric potentiators of agonist function at a G protein-coupled receptor (GPCR)-the adenosine A(1) receptor-their mechanism of action is still not fully understood. We now report the mechanistic basis for the complex behaviors noted for 2A3BTs at A(1) receptors. Using a combination of membrane-based and intact-cell radioligand binding, multiple signaling assays, and a native tissue bioassay, we found that the allosteric interaction between 2A3BTs and the agonists 2-chloro-N(6)-[(3)H]cyclopentyladenosine or (-)-N(6)-(2-phenylisopropyl)adenosine (R-PIA) or the antagonist [(3)H]8-cyclopentyl-1,3-dipropylxanthine is consistent with a ternary complex model involving recognition of a single extracellular allosteric site.

Cardioprotection induced by adenosine A1 receptor agonists in a cardiac cell ischemia model involves cooperative activation of adenosine A2A and A2B receptors by endogenous adenosine.

Extracellular adenosine concentrations increase within the heart during ischemia, and any exogenous adenosine receptor agonists therefore work in the context of significant local agonist concentrations. We evaluated the interactions between A1, A2A, A2B, and A3 receptors in the presence and absence of adenosine deaminase (ADA, which is used to remove endogenous adenosine) in a cardiac cell ischemia model. Simulated ischemia (SI) was induced by incubating H9c2(2-1) cells in SI medium for 12 hours in 100% N2 gas before assessment of necrosis using propidium iodide (5 microM) or apoptosis using AnnexinV-PE flow cytometry.