Figure 2.

Effect of ischemic PC on iNOS expression and activity in WT and iNOS^−/− mice. Tissue samples were obtained as described in the legend to Fig. 1. (A) Myocardial content of iNOS (cytosolic fraction). In WT mice, the iNOS protein content in the ischemic-reperfused region was increased by 47 ± 12% 24 h after ischemic PC. In iNOS^−/− mice, immunoreactive iNOS protein was undetectable, either after sham surgery or after ischemic PC. (B) Calcium-independent NOS (iNOS) activity in the cytosolic fraction. In WT mice, iNOS activity in the ischemic-reperfused region increased by 227% 24 h after ischemic PC. In iNOS^−/− mice, low levels of calcium-independent NOS activity were noted in iNOS^−/− mice, either after sham operation or after ischemic PC. These levels probably represent cNOS activity (20, 21). (C) Total myocardial content of nitrite and nitrate (NO_x). In WT mice, NO_x levels in the ischemic-reperfused region increased significantly 24 h after ischemic PC. In iNOS^−/− mice, ischemic PC did not bring about any increase in NO_x levels; furthermore, NO_x levels were significantly lower in iNOS^−/− mice compared with WT mice. Data are means ± SEM.