31P NMR analysis of intracellular pH of Swiss Mouse 3T3 cells: effects of extracellular Na+ and K+ and mitogenic stimulation

Abstract

Swiss mouse 3T3 cells grown on microcarrier beads were superfused with electrolyte solution during continuous NMR analysis. Conventional 31P and 19F probes of intracellular pH (pHc) were found to be impracticable. Cells were therefore superfused with 1 to 4 mM 2-deoxyglucose, producing a large intracellular, pH-sensitive signal of 2-deoxyglucose phosphate (2DGP). The intracellular incorporation of 2DGP inhibited the Embden-Meyerhof pathway. However, intracellular ATP was at least in part retained and the cellular responsivity to changes in extracellular ionic composition and to the application of growth factors proved intact. Transient replacement of external Na+ with choline or K+ reversibly acidified the intracellular fluids. Quiescent cells and mitogenically stimulated cells displayed the same dependence of shifts in pHc on external Na+ concentration (CoNa). PHc also depended on intracellular Na+ concentration (CcNa). Increasing ccNa by withdrawing external K+ (thereby inhibiting the Na,K-pump) caused reversible intracellular acidification; subsequently reducing CoNa produced a larger acid shift in pHc than with external K+ present. Comparison of separate preparations indicated that pHc was higher in stimulated than in quiescent cells. Transient administration of mitogens also reversibly alkalinized quiescent cells studied continuously. This study documents the feasibility of monitoring pHc of Swiss mouse 3T3 cells using 31P NMR analysis of 2DGP. The results support the concept of a Na/H antiport operative in these cells, both in quiescence and after mitogenic stimulation. The data document by an independent technique that cytoplasmic alkalinization is an early event in mitogenesis, and that full activity of the Embden-Meyerhof pathway is not required for the expression of this event.