2
PO
4
2
,4.7mMKCl,1.7mMCaCl
, 1.2 mM MgSO
, 20 mM sodium acetate, and 10 mM glucose, pH 7.4. The buffer was kept at 37 ฐC and bubbled continuously with 100% oxygen. A small waterjacketed chamber was used to keep the hearts at 37 ฐC. The hearts were stabilized for 15 min, and then global ischemia and reperfusion were established for 20 min and 2 h, respectively. Sham hearts were perfused for the 15 min stabilization period only. The heart effluents were collected for 1-min intervals at selected times for determination of coronary flow and lactate dehydrogenase release. At the end of the perfusions, the hearts were harvested and the ventricles were snap-frozen in liquid nitrogen and kept at −70 ฐC for later analysis. The frozen ventricles were crushed to a powder using a liquid nitrogen-chilled tissue pulverizer. For tissue analyses, weighed amounts of the frozen tissues were homogenized in the appropriate buffer using a microcentrifuge tube homogenizer. The protein content of the homogenates was determined by the Bradford method [36].
4
Coronary Flow and Lactate Dehydrogenase (LDH) Release
The heart effluents were collected for 1 min at selected time points during stabilization and reperfusion periods. Coronary flow rate was calculated as ml effluent/min/g wet weight of heart. The activity of LDH in the effluent samples was measured according to the method of Kornberg [37]. LDH activity was calculated as units/ml of coronary flow/ wet weight of the heart.
Caspase-3 Activity
Thirty mg of the frozen tissue was homogenized in 500 μl cold lysis buffer containing 10 mM Hepes,
2