Intracellular pH measurements using flow cytometry with 1,4-diacetoxy-2,3-dicyanobenzene

Modification of intracellular pH and thermotolerance development by amiloride

The intracellular pH (pHi) of cells heated at 45.0 degrees C in the presence or absence of amiloride and in choline chloride substituted sodium-free medium was measured with flow cytometry using the pH sensitive dye, carboxy-seminaphthorhodafluor (SNARF-1). Chinese hamster ovary (CHO) cells at pH 7.3 and low-pH-resistant (PHV2) cells at pH 6.6 were studied. Bimodal population distributions of pHi were obtained for both CHO and PHV2 cells following a treatment in which cells were heated 10 min at 45.0 degrees C, incubated 4 to 10 h at 37 degrees C, then reheated at 45 min at 45.0 degrees C. Amiloride or sodium-free medium modified the changes in pHi, but did not eliminate them entirely. Cells were sorted from the higher pHi and lower pHi subpopulations and plated for cell survival. The survival after both heat treatments was three to five-fold higher for cells sorted from the higher pHi subpopulation than cells sorted from the low pHi subpopulation. The development of thermotolerance was delayed in CHO cells but not in PHV2 cells when amiloride was present throughout the treatment regimen. Combining low pH with amiloride caused an even greater delay in thermotolerance development in CHO cells. However, the final fraction of thermotolerant cells after 14 h incubation was nearly identical, regardless of medium pH or the presence of amiloride.

Measurement of intracellular pH using flow cytometry with carboxy-SNARF-1

The new intracellular pH (pH(i)) dye carboxy-seminaphthorhodafluor (SNARF-1) was compared to the established dye 2,3-dicyanohydroquinone (DCH) using flow cytometry. Both dyes give high-resolution pH(i) measurements. SNARF-1 remains trapped within cells much longer than DCH, so that pH(i) can be monitored during and after treatments with chemicals or hyperthermia. The toxicity of the dyes is similar, and both dyes can be used at concentrations that result in low toxicity to cells. Adequate staining of cells with SNARF-1 is dependent on the cell concentration. The absolute pHi values indicated by SNARF-1 are higher than values measured with DCH. However, the trends measured by both dyes are consistent, and both are useful for making pH(i) measurements.

Analysis of lymphocyte activation and metabolism by flow cytometry

The use of flow cytometry for the study of lymphocyte activation and cellular metabolism continues to expand. This has permitted rapid progress in the understanding of the regulation of multiple intracellular ions, metabolic pathways, and the control of gene expression. Knowledge of these basic mechanisms of cellular homeostasis is now being applied to the flow cytometric study of immune dysregulation. Various flow cytometric techniques for measuring apoptosis are summarized.

Intracellular calcium and pH alterations induced by Escherichia coli endotoxin in rat hepatocytes

In this study, the fluorescent Ca2+ probe fura-2 and the fluorescent pH indicator BCECF have been used to monitor cytosolic free Ca2+ and intracellular pH (pHi), respectively, in isolated and cultured hepatocytes treated with Escherichia coli O111:B4 endotoxin. Uptake of 45Ca2+ was also measured to study the effect of endotoxin on the extracellular calcium influx. Endotoxin treatment produced a progressive increase of cytosolic Ca2+ in a dose-dependent manner caused by both induction of a significant release of Ca2+ from intracellular stores and stimulation of the extracellular calcium influx. The perturbation of Ca2+ homeostasis by endotoxin may cause an abnormal stimulation of physiological processes, developing lethal cell injury. Endotoxin also produced a significant decrease in the pHi of hepatocytes which can justify important metabolic alterations during endotoxicosis.

A method for calibration of flow cytometric wavelength shift fluorescence measurements

Recently, new fluorescent dyes have been introduced into flow cytometry which alter their spectral characteristics when changes occur in certain cell features, e.g., intracellular pH or calcium ion concentration. Such changes may be determined by measuring the fluorescence intensity ratio in two different wavelength ranges (5). Here a new method is described, which simplifies the use of steadily flowing fluids for calibration. The pulse electronics of a flow cytometer cannot process the static fluorescence signals of a streaming fluid. If, however, the exciting or emitted fluorescence light of a calibration fluid is made pulsating, the flow cytometer electronics can evaluate those pulses. The new calibration procedure uses measurement of two wavelength windows shown in a two-parameter display to generate an absolute calibration scale. Measurement of the spectral shift in calibration fluids under identical instrumental settings provides absolute values that measurements of intracellular concentrations can be referred to.