Modification of the ATP-Induced Increase in

BACKGROUND: It is generally accepted that the plasma membrane of mammalian ventricular myocytes regulates the cytosolic concentration of Ca(2+). In this study we investigated the effects of some P2-purinoceptor antagonists and metals such as copper and zinc on the adenosine triphosphate (ATP)-induced increase in intracellular concentration of free Ca(2+) ([Ca(2+)](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 [Ca(2+)](i) over the basal value, and 10 µM cibacron blue or verapamil virtually abolished it. The ATP-induced increase in [Ca(2+)](i) was not observed in Ca(2+)- or Mg(2+)-free buffers. Incubation of cells with ZnCl(2) produced a significant depression of the ATP-induced increase in [Ca(2+)](i); 25 µM Zn(2+) decreased the peak response to approximately 50% of the control value. The ATP-induced increase in [Ca(2+)](i), was inhibited by low concentrations (1-5 µM) of Cu(2+) but was markedly augmented by high concentrations (25 µM) of Cu(2+). The increase in the [Ca(2+)](i) response to cron blue, and Zn(2+), but not by ryanodine or caffeine pretreatment. CONCLUSIONS: The ATP-induced increase in [Ca(2+)](i) is dependent on the extracellular concentrations of Ca(2+) as well as Mg(2+) and is antagonized by cibacron blue and Zn(2+). On the other hand, Cu(2+) produced a biphasic response to the ATP-induced increase in [Ca(2+)](i) in cardiomyocytes.