The Relationship Between Intracellular pH and Cell Cycle in Cultured Animal Cells Using SNARF-1 Indicator

The internal pH (pHi) of animal cells is an important physiological parameter, as cells can function only in a narrow range of pHi values (near neutral). The regulation of pHi is achieved through the action of the Na⁺-H⁺ ion exchanger [1,2]. Other pumps are also likely to play a role (e.g., the HCO₃ ^_-Cl^-exchanger). Cells have a large negative membrane potential, which would cause the passive diffusion of H⁺ ions across the plasma membrane. Without the uphill extrusion of H⁺ ions out of the cells through the action of the Na⁺-H⁺-exchanger, the cytoplasm of the cells would be too acidic for the cells to function. Through the action of the Na⁺-K⁺ ATPase, the concentration of Na⁺ inside the cell is kept well below the concentration of Na⁺ outside the cell. This provides the thermodynamic driving force for H⁺ extrusion. However, a greater efflux of H⁺ can lead to an increase in pHi, a condition that is normally associated with an increase in cell activity.