Biochemical and morphological correlates of cardiac ischaemia: Contractile proteins.

Experimentally-induced ischaemia in the dog heart was produced by ligating the left circumflex artery. Myosin B isolated from the ischaemic portion of the myocardium differed from myosin B isolated from control tissue in its diminished response to the calcium chelator ethyleneglycol bis (beta-amino-ethylether)-N, N'-tetraacetic acid (EGTA). In the presence of EGTA, ischaemic myosin B required 2.5 +/- 0.5 min for completion of superprecipitation, whereas control myosin B required 6.6 +/- 2.5 min. Likewise, the Mg++ -activated ATPase activity of ischaemic myosin B was inhibited by EGTA to a lesser degree than control myosin B. Experiments with reconstituted myosin B using desensitized control myosin B and regulatory proteins suggest that ischaemia induces changes in the regulatory proteins (troponin and tropomyosin).