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

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.