A new method of quantifying glutathione levels in freshly isolated single superfused rat cardiomyocytes.

INTRODUCTION: Glutathione (GSH) is an important antioxidant in the heart whose content changes during cardiac insults. However, there are currently no methods for continuously monitoring free cytoplasmic GSH levels in single isolated and superfused cardiomyocytes exposed to normal and pathological conditions.
METHODS: GSH was measured using CellTracker Blue CMAC (Molecular Probes), a member of a new family of thiol-sensitive dyes. The fluorescence of 5 microM CellTracker Blue CMAC was measured in various solutions containing glutathione-S-transferase and in freshly isolated single superfused cardiomyocytes using an inverted fluorescence microscope. The cardiomyocytes were isolated by standard procedures and loaded with either CellTracker Blue CMAC or monochlorobimane by 15 min of shaking incubation in the dark at room temperature followed by centrifugation with resuspension of the cells in dye-free media. Cell volume was calculated from the 3H2O and [14C]sucrose space.
RESULTS: CellTracker Blue CMAC fluorescence was linearly proportional to 0-100 microM GSH, as described by the equation: Y = 182.2 (X) + 681.6 (r2 = .99, P < .001). Fluorescence was not affected by changing the glutathione-S-transferase level, the calcium concentration, or the pH, neither was the fluorescence quenched by H2O2 or cyanide. Exposure of freshly isolated single superfused cardiomyocytes to oxidative stress in the presence of 0-1 mM H2O2 caused a progressive decrease in cellular GSH. In contrast, brief exposure to metabolic inhibition in the presence of 2.5 mM NaCN evoked a significant increase in cardiomyocyte GSH followed by a return to control levels during washoff. In comparison to monochlorobimane, cells loaded with CellTracker Blue CMAC gave a stronger signal with better cellular retention of the probe. DISCUSSION: These results suggest that CellTracker Blue CMAC fluorescence will be a good tool for measuring GSH in freshly isolated single superfused cardiomyocytes because it shows the expected changes to oxidative stress and metabolic inhibition, and is reversible.