Myocardial infarct sizes after Sp1 repression. (A) CD39^−/− mice or littermate controls matched in age, sex, and gender (CD39^+/+ mice) were exposed to 45 minutes of myocardial ischemia after 2 hours of infusion of control siRNA (SCR siRNA) or siRNA specific for Sp1 (Sp1 siRNA) via a catheter placed with its infusion port into the left ventricle. Myocardial infarct sizes were measured by double staining of cardiac tissue with Evan blue and TTC. Infarct sizes are expressed as the percentage of the area at risk that underwent infarction (mean ± SD, n = 6). *P < .05 compared to control siRNA–treated mice (SCR); **P < .05 compared to wild-type mice (cd39^+/+). (B) Reconstitution with soluble apyrase. C57BL/6J mice underwent treatment with control siRNA (SCR siRNA) or siRNA specific for Sp1 (Sp1 siRNA, see description for panel A). Thirty minutes before coronary ischemia, they were treated intraperitoneally with soluble apyrase (+Apyrase, 80 U/kg) or vehicle. After 45 minutes of myocardial ischemia and 2 hours of reperfusion, infarct sizes were determined by Evan blue and TCC double staining (mean ± SEM, n = 6). *P < .05 compared to vehicle-treated mice (Vehicle); **P < .05 compared to control siRNA–treated mice (SCR).