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Comparative effects of phenobarbital, DDT, and lindane on mouse hepatocyte gap junctional intercellular communication
J E Klaunig1, R J Ruch, C M Weghorst
1Department of Pathology, Medical College of Ohio, Toledo 43614.
Abstract:
Gap junctional intercellular communication appears to be important in the regulation of cellular homeostasis, differentiated cell functions, and growth control in adult tissues. Interruption of intercellular communication by chemical compounds has been shown to be a sublethal response to a number of tumor promoters. The mechanism by which tumor promoters inhibit intercellular communication remains unresolved. In the present study the kinetics of inhibition of mouse hepatocyte gap junctional intercellular communication (measured by dye coupling) by three well-established hepatic tumor promoters [phenobarbital, 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT), and gamma-hexachlorocyclohexane (lindane)] are compared. All three compounds inhibited intercellular communication in a time- and dose-dependent manner in both freshly plated and 24-hr-old hepatocyte cultures. Following removal of the tumor promoters from the culture medium, intercellular communication was reestablished within 0.5 hr (phenobarbital) to 1.5 hr (DDT and lindane). Prolonged treatment of hepatocytes for up to 48 hr with the three promoters resulted in the continued inhibition of intercellular communication by lindane and DDT, but the development of refractoriness to phenobarbital-induced inhibition of intercellular communication. Concomitant treatment with combinations of the three promoters showed an additive effect of the compounds on inhibition of intercellular communication. Inhibition of intercellular communication by phenobarbital was prevented by addition of the cytochrome P450 enzyme inhibitor SKF-525A. SKF-525A had no effect on the inhibition of intercellular communication induced by lindane or DDT. Coincubation of the three promoters with the cAMP analog 8-bromo-cAMP prevented the promoter-induced inhibition of intercellular communication.
Insights
Tumor promoters like phenobarbital, DDT, and lindane inhibit cell communication. While DDT and lindane cause lasting effects, cells become resistant to phenobarbital over time.
Area of Science:
- Cell biology
- Toxicology
- Biochemistry
Background:
- Gap junctional intercellular communication (GJIC) is crucial for tissue homeostasis and growth control.
- Tumor promoters are known to disrupt GJIC, but the underlying mechanisms are unclear.
Purpose of the Study:
- To compare the kinetics of GJIC inhibition by three hepatic tumor promoters: phenobarbital, DDT, and lindane.
- To investigate the reversibility and long-term effects of these promoters on GJIC.
- To explore potential mechanisms, including cytochrome P450 and cAMP pathways.
Main Methods:
- Primary mouse hepatocytes were cultured and treated with phenobarbital, DDT, and lindane.
- Dye coupling assays were used to measure GJIC inhibition.
- Experiments involved varying exposure times, doses, and the use of enzyme inhibitors (SKF-525A) and cAMP analogs (8-bromo-cAMP).
Main Results:
- All three promoters inhibited GJIC in a time- and dose-dependent manner.
- GJIC recovered within 0.5-1.5 hours after promoter removal.
- Prolonged exposure led to refractoriness to phenobarbital but not to DDT or lindane.
- SKF-525A blocked phenobarbital's effect but not DDT's or lindane's, while 8-bromo-cAMP prevented inhibition by all three.
Conclusions:
- Tumor promoters exhibit distinct kinetics and mechanisms in inhibiting GJIC.
- Phenobarbital's effect appears mediated by cytochrome P450, while DDT and lindane's mechanisms differ.
- The cAMP pathway is involved in preventing promoter-induced GJIC inhibition by all tested compounds.