Biochemical and morphological correlates of cardiac ischaemia: contractile proteins

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Abstract
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 (β-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).

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