given cell. Nuclear magnetic resonance In addition to using pH-sensitive electrodes and dyes to measure pHi, Nuclear Magnetic Resonance (NMR) spectroscopy can also be used to quantify pHi. NMR, typically speaking, reveals information about the inside of a cell by placing the cell in an environment with a potent magnetic field. Based on the ratio between the concentrations of protonated, compared to deprotonated, forms of phosphate compounds in a given cell, the internal pH of the cell can be determined. Additionally, NMR may also be used to reveal the presence of intracellular sodium, which can also provide information about the pHi. Using NMR Spectroscopy, it has been determined that lymphocytes maintain a constant internal pH of 7.17± 0.06, though, like all cells, the intracellular pH changes in the same direction as extracellular pH. pH-sensitive GFPs To determine the pH inside organelles, pH-sensitive GFPs are often used as part of a noninvasive and effective technique. By using cDNA as a template along with the appropriate primers, the GFP gene can be expressed in the cytosol, and the proteins produced can target specific regions within the cell, such as the mitochondria, golgi apparatus, cytoplasm, and endoplasmic reticulum. If certain GFP mutants that are highly sensitive to pH in intracellular environments are used in these experiments, the relative amount of resulting fluorescence can reveal the approximate surrounding pH. References Cell biology