INTERACTIONS BETWEEN INTRACELLULAR pH AND CALCIUM IN-SINGLE MOUSE NEUROBLASTOMA (N2A) AND RAT PHEOCHROMOCYTOMA CELLS (PC12)

¹ Department of Physiological Sciences, The Medical School, The University, Framlington Place, Newcastle upon Tyne NE2 4HH

Intracellular pH (pH_i) 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 pH_i 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 Ca_i²⁺ have been reported between neurites and the cell body, experiments were performed to examine the possible interactions between pH_i and Ca_i²⁺. Intracellular calcium was measured using the fluorescent Ca²⁺-sensitive dye Indo-1. An increase in pH_i, on application of NH₄Cl, resulted in a transient elevation of Ca_i²⁺. On subsequent acidification, on removal of NH₄Cl, there was a further transient increase in Ca_i²⁺. These changes in Ca_i²⁺ were also present in solutions with low calcium suggesting that Ca_i²⁺ 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 Ca_i²⁺ and modulated by pH_i.

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