Inhibition of mouse hepatocyte intercellular communication by paraquat-generated oxygen free radicals

Intercellular communication through gap junctions functions in electrical synapsing, homeostasis, hormonal response, embryogenesis, and growth control. Many neurotoxicants, teratogens, and carcinogens are capable of inhibiting gap junctional intercellular communication and this effect may be related to their toxic activity. In addition, many of these toxic agents are capable of stimulating oxygen free radical production in cells. The purpose of this study was to determine if oxygen free radicals at noncytotoxic levels could inhibit intercellular communication in primary cultured mouse hepatocytes. Intercellular communication was evaluated in 24-hr-old cultures of male B6C3F1/Cr1BR mouse hepatocytes by microinjection of fluorescent Lucifer Yellow CH dye and visualization of dye spread to adjacent hepatocytes (dye-coupling). Dye-coupling was rapidly established in freshly plated primary cultured hepatocytes reaching a level of over 90% after 24 hr of culture. After 24 hr, dye-coupling paralleled hepatocyte survival. Treatment of hepatocyte cultures with noncytotoxic concentrations of paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride; PQ) (0.5-5 mM), hydrogen peroxide (0.5-2 mM), glucose oxidase (0.1 U/ml), or xanthine oxidase (0.2 U/ml plus 1 mM xanthine) for exposure durations of 2-8 hr resulted in concentration-dependent decreases in dye-coupling. Addition of the antioxidants DPPD (N,N-diphenyl-p-phenylenediamine; 25 microM) and vitamin E (D,L-alpha-tocopherol acetate; 100 microM) decreased the inhibitory effect of PQ on dye-coupling. In contrast, addition of the catalase inhibitor 3-amino-1,2,4-triazole or the glutathione depletor diethylmaleate to PQ-treated cultures potentiated PQ-induced inhibition of dye-coupling. PQ stimulated NADPH-dependent mouse liver microsomal superoxide radical production. Thus, one effect of prooxidant compounds appears to be the inhibition of IC. This effect may be important in the sublethal toxicity of oxygen radical generating compounds.