Modification of the ATP-Induced Increase in [Ca2+]i by Copper and Zinc in Rat Cardiomyocytes

Abstract

Background: It is generally accepted that the plasma membrane of mammalian ventricular myocytes regulates the cytosolic concentration of Ca2+. In this study we investigated the effects of some P2-purinoceptor antagonists and metals such as copper and zinc on the ade nosine triphosphate (ATP)-induced increase in intracellular concentration of free Ca2+ ([Ca2+]i). Methods and Results: Cardiomyocytes were isolated from adult male Sprague-Dawley rats loaded with Fura-2, and fluorescence measurements were performed by employing stirred cell suspensions at room temperature. ATP (50 μM) increased [Ca2+]i over the basal value, 10 μM ryanodine pretreatment partially attenuated the ATP-evoked increase in [Ca2+]i, and 10 μM cibacron blue or verapamil virtually abolished it. The ATP-induced increase in [Ca 2+]i was not observed in Ca2+- or Mg2+-free buffers. Incubation of cells with ZnCl2 pro duced a significant depression of the ATP-induced increase in [Ca2+]i; 25 μM Zn2+ decreased the peak response to approximately 50% of the control value. The ATP-induced increase in [Ca2+]i, was inhibited by low concentrations (1-5 μM) of Cu2+ but was markedly augmented by high concentrations (25 μM) of Cu2+. The increase in the [Ca2+] i response to ATP induced by 25 μM Cu2+ was Mg 2+ dependent and was prevented by verapamil, ciba cron blue, and Zn2+, but not by ryanodine or caffeine pretreatment. Conclusions: The ATP-induced increase in [Ca2+]i is dependent on the extracellular con centrations of Ca2+ as well as Mg2+ and is antagonized by cibacron blue and Zn2+. On the other hand, Cu2+ produced a biphasic response to the ATP-induced increase in [Ca2+]i in cardiomyocytes.