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Abstract
ATP-dependent Ca 2+ accumulation and (Mg 2+ + Ca 2+)ATPase activities were determined in cardiac sarcoplasmic reticulum (SR) from control, adrenalectomized and adrenalectomized-dexamethasone-treated rats. SR from adrenalectomized rats displayed significantly diminished rates (∼40 to 50%, P < 0.001) of Ca 2+ accumulation compared to SR from control rats. The decreased Ca 2+ accumulating activity of the membranes from adrenalectomized compared to control rats could be observed at varying Ca 2+ concentrations (0.5 to 11.9 μ m); kinetic analysis showed that the velocity of Ca 2+ transport but not the apparent affinity of the transport system for Ca 2+ was altered by adrenalectomy. ATPase activities (with Mg 2+ or with Mg 2+ + Ca 2+) of SR were not altered significantly following adrenalectomy. In vivo administration of dexamethasone to adrenalectomized rats led to a partial (75 to 80%) yet significant ( P < 0.01 to 0.05) restoration of Ca 2+ accumulating activity of SR towards normal; dexamethasone-treatment caused decrease in basal (Mg 2+)ATPase activity and enhancement in (Mg 2+ + Ca 2+)ATPase activity. When added in vitro, dexamethasone had no effect on Ca 2+ accumulating and ATPase activities of SR from control or adrenalectomized rats. These findings imply an important role for glucocorticoids in the maintenance of membrane Ca 2+ transport function, and therefore, normal myocardial contractility.
Published Version
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