Intracellular pH changes of cultured bovine aortic endothelial cells in response to ATP addition

The changes of the intracellular pH (pH i) of cultured bovine aortic endothelial cells were fluorometrically monitored using 2′,7′-bis(carboxyethyl)carboxyfluorescein (BCECF). A biphasic pH i change was observed by addition of ATP: an initial acidification followed by an alkalinization of about 0.2 pH unit above the resting level of pH i 7.23. The alkalinization was dependent on [Na +] o and [H +] o, and was inhibited by 5-( N,N-hexamethylene)amiloride, indicating that the alkalinization is mediated by the Na +/H + exchanger. The 50% effective concentration of ATP was about 1.4 μM. ADP similarly induced pH i changes, whereas AMP and adenosine were inactive. The pH i changes induced by ATP were dependent on the extracellular Ca 2+, and the addition of calcium ionophore A23187 induced similar pH i changes. The results indicate that ATP activates the Na +/H + exchanger in cultured bovine aortic endothelial cells and the activation is mediated by the P 2-purinergic receptor and is dependent on the extracellular Ca 2+.