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Interactions between intracellular pH and calcium in single mouse neuroblastoma (N2A) and rat pheochromocytoma cells (PC12).

Intracellular pH (pHi) was measured at the tips of extending neurites and in the corresponding cell bodies of single cultured mouse neuroblastoma (N2A) and rat pheochromocytoma cells (PC12) using the fluorescent dye 2,3-di-cyanohydroquinone (DCH). It was observed that pHi at the tip of an extending neurite was consistently 0.2-0.3 pH units higher than pHi in the cell body. Experiments performed on whole cells to establish the types of cellular mechanism which could be responsible for such regional differences demonstrate the presence of Na+-H+ exchange and Cl- HCO3- exchange in these cells. Since regional variations in Ca2i+ have been reported between neurites and the cell body, experiments were performed to examine the possible interactions between pHi and Ca2i+. Intracellular calcium was measured using the fluorescent Ca2+-sensitive dye Indo-1. An increase in pHi, on application of NH4Cl, resulted in a transient elevation of Ca12i+. On subsequent acidification, on removal of NH4Cl, there was a further transient increase in Ca2i+. These changes in Ca2i+ were also present in solutions with low calcium suggesting that Ca2i+ is mobilized from within the cell. The results are discussed in terms of possible mechanisms whereby the extension and retraction of cell processes could be influenced by Ca2i+ and modulated by pHi.