[Changes in Ca++-ATPase activity of rat myocyte under cardioplegia]

Ischemic changes of cardiac muscle under cardioplegia must be evaluated at a subcellular level from functional aspects using cytochemical procedures as well as from morphological aspects. In this study, kinetics of Ca++-ATPase activity of rat cardiac myocytes under GIK-cardioplegia was estimated using a new one-step lead citrate method reported by Ando et al. The Ca++-ATPase activity of mitochondria in myocytes which had temporally increased at 15 minutes after initiation of cardioplegia, showed a slight decrease at 30 minutes and then almost disappeared at 60 minutes. At 60 minutes after the cardioplegia, the Ca++-ATPase activities of the sarcoplasmic reticula and myofilaments were well preserved and electromicroscopic findings of the myocytes remained normal. Thus, changes of Ca++-ATPase activity of mitochondria are considered to reflect ischemic damage of myocyte sharply, proceeding morphological changes in ultrastructure.