Abstract
Calcium is believed to provide feedback between myocardial energy consumption and production. Calcium content was proved to increase in mitochondria (MT) isolated from (1) stimulated hearts, and (2) hearts of increased contractility. In this work we compared Ca 2+ content in the intact MT of skinned strips excised at 0°C from previously stimulated or rested guinea-pig ventricles equilibrated with 43Ca and in single rested or stimulated myocytes. In both preparations Ca 2+ was released from MT by means of CCCP (carbonyl cyanide m-chlorophenyl-hydrazone; 100 μ m). CCCP released 1.58 ± 0.55 nmol Ca 2+/mg of MT protein from the strips of rested hearts and 3.86 ± 1.12 nmol Ca 2+/mg of MT protein from the stimulated muscles. Stimulated myocytes responded to the close micro-injection of CCCP with transient contracture which was not inhibited by caffeine (10 m m) or ryanodine (0.1 μ m, 45 min), although the time-course of the contracture was changed. Contracture could not be initiated in rested cells. It is suggested that in rested myocytes MT contain much less Ca 2+ than in stimulated ones.
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