The role of intracellular pH in cell growth arrest induced by ATP

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Abstract
In this study, we investigated ionic mechanisms involved in growth arrest induced by extracellular ATP in androgen-independent prostate cancer cells. Extracellular ATP reversibly induced a rapid and sustained intracellular pH (pHi) decrease from 7.41 to 7.11. Inhibition of Ca2+influx, lowering extracellular Ca2+, and buffering cytoplasmic Ca2+inhibited ATP-induced acidification, thereby demonstrating that acidification is a consequence of Ca2+entry. We show that ATP induced reuptake of Ca2+by the mitochondria and a transient depolarization of the inner mitochondrial membrane. ATP-induced acidification was reduced after the dissipation of the mitochondrial proton gradient by rotenone and carbonyl cyanide p-trifluoromethoxyphenylhydrazone, after inhibition of Ca2+uptake into the mitochondria by ruthenium red, and after inhibition of the F0F1-ATPase with oligomycin. ATP-induced acidification was not induced by either stimulation of the Cl−/HCO3−exchanger or inhibition of the Na+/H+exchanger. In addition, intracellular acidification, induced by an ammonium prepulse method, reduced the amount of releasable Ca2+from the endoplasmic reticulum, assessed by measuring change in cytosolic Ca2+induced by thapsigargin or ATP in a Ca2+-free medium. This latter finding reveals cross talk between pHiand Ca2+homeostasis in which the Ca2+-induced intracellular acidification can in turn regulate the amount of Ca2+that can be released from the endoplasmic reticulum. Furthermore, pHidecrease was capable of reducing cell growth. Taken together, our results suggest that ATP-induced acidification in DU-145 cells results from specific effect of mitochondrial function and is one of the major mechanisms leading to growth arrest induced by ATP.