Low-level chemiluminescence of isolated hepatocytes.

1. Oxygenation of isolated hepatocytes leads to an increased emission of low level chemiluminescence and to an accumulation of malondialdehyde, both occurring after a lag phase of about 20--40 min. 2. Spectral analysis of oxygen-induced chemiluminescence of isolated hepatocytes showed three bands at 460, 560 and 640 nm, with two shoulders at 525 and 615 nm. Singlet molecular oxygen, formed during the free radical process accompanying lipid peroxidation, is identified as the main source of light emission, on the basis of comparison with spectra of singlet oxygen produced in chemical systems [Khan, A. U. and Kasha, M. (1963) J. Am. Chem. Soc. 92, 3293--3300]. 3. Hepatocytes from phenobarbital-pretreated rats, or glutathione-depleted hepatocytes showed a threefold increase in both maximal chemiluminescence intensity and malondialdehyde accumulated, as compared with control cells, whereas the lag phase was not modified by the pretreatments. 4. Glutathione-depleted hepatocytes did not show any increase in spontaneous lipid peroxidation as reflected by either malondialdehyde accumulation or chemiluminescence. A dissociation between both parameters was observed on addition of dithioerythritol: chemiluminescence intensity decreased while the malondialdehyde content remained unaltered. 5. It is concluded from these experiments that low-level chemiluminescence emitted from hepatocytes at wavelengths beyond 600 nm ('red band') monitors the steady-state concentration of singlet molecular oxygen, providing a useful tool to examine oxygen-dependent radical damage. Continuous monitoring of singlet oxygen levels affords an advantage over parameters measuring accumulative effects.