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 2AARs) inhibits reperfusion injury, we hypothesized that ATL146e (a selective A 2AAR agonist) might protect hearts in part by reducing cardiac mast cell degranulation. Hearts were isolated from five groups of congenic mice: A 2AAR ϩ/ϩ mice, A2AAR Ϫ/Ϫ mice, mast celldeficient (Kit W-sh/W-sh ) mice, and chimeric mice prepared by transplanting bone marrow from A 2AAR Ϫ/Ϫ or A2AAR ϩ/ϩ mice to radiation-ablated A 2AAR ϩ/ϩ mice. Six weeks after bone marrow transplantation, cardiac mast cells were repopulated with Ͼ90% 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 Ϯ 2% to 24 Ϯ 2% and 22 Ϯ 2% in ATL146e-and CGS-21680-treated hearts, respectively (P Ͻ 0.05) and significantly reduced mast cell degranulation, measured as tryptase release into reperfusion buffer. These changes were absent in A 2AARϪ/Ϫ hearts and in hearts from chimeric mice with A2AARϪ/Ϫ bone marrow. Vehicle-treated Kit W-sh/W-sh mice had lower IS (11 Ϯ 3%) than WT mice, and ATL146e had no significant protective effect (16 Ϯ 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 A2AAR activation is cardioprotective in the isolated heart, at least in part by attenuating resident mast cell degranulation.Langendorff; tryptase; ATL146e; CGS-21680; bone marrow chimera MAST CELLS CONTRIBUTE to immune responses with both sentinel and effector roles in host defense and inflammation. The activation of mast cells has been found to have protective or deleterious effects in response to tissue infection or injury (22,29). This is due in part to tissue-specific heterogeneity of mast cell function (3, 48). In the heart, degranulation of resident cardiac mast cells mediates injurious effects during experimental ischemia-reperfusion (I/R) injury and myocardial infarction (MI). These deleterious effects are mediated by multiple mechanisms, including a local renin-angiotensin axis (18,26,41), histamine and prostanoid-induced ventricular arrhythmogenesis (36), and the initiation of a cytokine cascade resulting in increased ICAM-1 expression and neutrophil extravasation (13,42). In addition, resident cardiac mast cells contribute to the ventricular hypertrophic response during chronic cardiac volume overload (6,16,32,33). In the isolated heart, oxidative stress from I/R is sufficient to stimulate degranulation of resident cardiac mast cells (13). Mast cell stabilizers such as ketotifen an...

. Altered sinus nodal and atrioventricular nodal function in freely moving mice overexpressing the A1 adenosine receptor. Am J Physiol Heart Circ Physiol 285: H145-H153, 2003. First published March 13, 2003 10.1152/ ajpheart.01036.2002To investigate whether altered function of adenosine receptors could contribute to sinus node or atrioventricular (AV) nodal dysfunction in conscious mammals, we studied transgenic (TG) mice with cardiac-specific overexpression of the A 1 adenosine receptor (A1AR). A Holter ECG was recorded in seven freely moving littermate pairs of mice during normal activity, exercise (5 min of swimming), and 1 h after exercise. TG mice had lower maximal heart rates (HR) than wild-type (WT) mice (normal activity: 437 Ϯ 18 vs. 522 Ϯ 24 beats/min, P Ͻ 0.05; exercise: 650 Ϯ 13 vs. 765 Ϯ 28 beats/min, P Ͻ 0.05; 1 h after exercise: 588 Ϯ 18 vs. 720 Ϯ 12 beats/min, P Ͻ 0.05; all values are means Ϯ SE). Mean HR was lower during exercise (589 Ϯ 16 vs. 698 Ϯ 34 beats/min, P Ͻ 0.05) and after exercise (495 Ϯ 16 vs. 592 Ϯ 27 beats/min, P Ͻ 0.05). Minimal HR was not different between genotypes. HR variability (SD of RR intervals) was reduced by 30% (P Ͻ 0.05) in TG compared with WT mice. Pertussis toxin (n ϭ 4 pairs, 150 g/kg ip) reversed bradycardia after 48 h. TG mice showed first-degree AV nodal block (PQ interval: 42 Ϯ 2 vs. 37 Ϯ 2 ms, P Ͻ 0.05), which was diminished but not abolished by pertussis toxin. Isolated Langendorffperfused TG hearts developed spontaneous atrial arrhythmias (3 of 6 TG mice vs. 0 of 9 WT mice, P Ͻ 0.05). In conclusion, A 1AR regulate sinus nodal and AV nodal function in the mammalian heart in vivo. Enhanced expression of A 1AR causes sinus nodal and AV nodal dysfunction and supraventricular arrhythmias. heart rate regulation; autonomous nervous system; heart rate variability; sinus node dysfunction; atrioventricular block; atrial fibrillation

. Effect of modulating cardiac A1 adenosine receptor expression on protection with ischemic preconditioning. Am J Physiol Heart Circ Physiol 290: H1469 -H1473, 2006. First published November 18, 2005 doi:10.1152/ajpheart.00181.2005.-Activation of A1 adenosine receptors (A1ARs) may be a crucial step in protection against myocardial ischemia-reperfusion (I/R) injury; however, the use of pharmacological A1AR antagonists to inhibit myocardial protection has yielded inconclusive results. In the current study, we have used mice with genetically modified A1AR expression to define the role of A1AR in intrinsic protection and ischemic preconditioning (IPC) against I/R injury. Normal wild-type (WT) mice, knockout mice with deleted (A1KO Ϫ/Ϫ ) or single-copy (A1KO ϩ/Ϫ ) A1AR, and transgenic mice (A1TG) with increased cardiac A1AR expression underwent 45 min of left anterior descending coronary artery occlusion, followed by 60 min of reperfusion. Subsets of each group were preconditioned with short durations of ischemia (3 cycles of 5 min of occlusion and 5 min of reperfusion) before index ischemia. Infarct size (IF) in WT, A1KO ϩ/Ϫ , and A1KO Ϫ/Ϫ mice was (in % of risk region) 58 Ϯ 3, 60 Ϯ 4, and 61 Ϯ 2, respectively, and was less in A1TG mice (39 Ϯ 4, P Ͻ 0.05). A strong correlation was observed between A1AR expression level and response to IPC. IF was significantly reduced by IPC in WT mice (35 Ϯ 3, P Ͻ 0.05 vs. WT), A1KO ϩ/Ϫ ϩ IPC (48 Ϯ 4, P Ͻ 0.05 vs. A1KO ϩ/Ϫ ), and A1TG ϩ IPC mice (24 Ϯ 2, P Ͻ 0.05 vs. A1TG). However, IPC did not decrease IF in A1KO Ϫ/Ϫ ϩ IPC mice (63 Ϯ 2). In addition, A1KO Ϫ/Ϫ hearts subjected to global I/R injury demonstrated diminished recovery of developed pressure and diastolic function compared with WT controls. These findings demonstrate that A1ARs are critical for protection from myocardial I/R injury and that cardioprotection with IPC is relative to the level of A1AR gene expression. myocardial ischemia-reperfusion injury; functional genomics; genetically altered mice

We tested the hypothesis that myocardial ischemia-reperfusion (I/R)-induced apoptosis is attenuated in transgenic mice overexpressing cardiac A(1) adenosine receptors. Isolated hearts from transgenic (TG, n = 19) and wild-type (WT, n = 22) mice underwent 30 min of ischemia and 2 h of reperfusion, with evaluation of apoptosis, caspase 3 activity, function, and necrosis. I/R-induced apoptosis was attenuated in TG hearts. TG hearts had less I/R-induced apoptotic nuclei (0.88 +/- 0.10% vs. 4.22 +/- 0.24% terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells in WT, P< 0.05), less DNA fragmentation (3.30 +/- 0.38-fold vs. 4.90 +/- 0.39-fold over control in WT, P < 0.05), and less I/R-induced caspase 3 activity (145 +/- 25% over nonischemic control vs. 234 +/- 31% in WT, P < 0.05). TG hearts also had improved recovery of function and less necrosis than WT hearts. In TG hearts pretreated with LY-294002 (3 microM) to evaluate the role of phosphosinositol-3-kinase in acute signaling, there was no change in the functional protection or apoptotic response to I/R. These data suggest that cardioprotection with transgenic overexpression of A(1) adenosine receptors involves attenuation of I/R-induced apoptosis that does not involve acute signaling through phosphoinositol-3-kinase.