Distribution of the monochlorobimane-glutathione conjugate between nucleus and cytosol in isolated hepatocytes.

The nuclear/cytoplasmic distributions of the GSH and N-acetylcysteine conjugates of monochlorobimane (MCB) have been studied in rat hepatocytes in primary culture after microinjection into the cytoplasm. The immediately occurring fluorescence (within 1-2 s) in the nucleus was much greater than that in the cytoplasm. Other water-soluble fluorescent markers such as Cascade Blue, 6-carboxyfluorescein and Lucifer Yellow also exhibited a similar nuclear localization. MCB, which is poorly soluble in water, gave similar results whether exposed to the exterior of the cell or microinjected as a solution in ethanol. It is concluded that the fluorophores studied here diffuse into the nucleus and accumulate there, including MCB-GSH formed intracellularly from MCB and GSH. Therefore MCB may be of limited value in estimating concentrations of GSH in the nucleus and the cytoplasm, as recently suggested by Bellomo, Vairetti, Stivala, Mirabelli, Richelmi and Orrenius [(1992) Proc. Natl. Acad. Sci. U.S.A. 89, 4412-4416].