Rork TH, Wallace KL, Kennedy DP, Marshall MA, Lankford AR, Linden J. Adenosine A(2A) receptor activation reduces infarct size in the isolated, perfused mouse heart by inhibiting resident cardiac mast cell degranulation. Am J Physiol Heart Circ Physiol 295: H1825-H1833, 2008; doi:10.1152/ajpheart.495.2008.- Mast cells are found in the heart and contribute to reperfusion injury following myocardial ischemia. Since the activation of A(2A) adenosine receptors (A(2A)ARs) inhibits reperfusion injury, we hypothesized that ATL146e (a selective A(2A)AR agonist) might protect hearts in part by reducing cardiac mast cell degranulation. Hearts were isolated from five groups of congenic mice: A(2A)AR(+/+) mice, A(2A)AR(+/+) mice, mast cell-deficient (Kit(W-sh/W-sh)) mice, and chimeric mice prepared by transplanting bone marrow from A(2A)AR(-/-) or A(2A)AR(-/-) mice to radiation-ablated A(2A)AR(+/+) mice. Six weeks after bone marrow transplantation, cardiac mast cells were repopulated with >90% donor cells. In isolated, perfused hearts subjected to ischemia-reperfusion injury, ATL146e or CGS-21680 (100 nmol/l) decreased infarct size (IS; percent area at risk) from 38 +/- 2% to 24 +/- 2% and 22 +/- 2% in ATL146e- and CGS-21680-treated hearts, respectively (P < 0.05) and significantly reduced mast cell degranulation, measured as tryptase release into reperfusion buffer. These changes were absent in A(2A)AR(-/-) hearts and in hearts from chimeric mice with A(2A)AR(-/-) bone marrow. Vehicle-treated Kit(W-sh/W-sh) mice had lower IS (11 +/- 3%) than WT mice, and ATL146e had no significant protective effect (16 +/- 3%). These data suggest that in ex vivo, buffer-perfused hearts, mast cell degranulation contributes to ischemia-reperfusion injury. In addition, our data suggest that A(2A)AR activation is cardioprotective in the isolated heart, at least in part by attenuating resident mast cell degranulation.
