title: Effects of 12-O-tetradecanoylphorbol-13-acetate (TPA), retinoic acid and diazepam on intercellular communication in a monolayer of rat liver epithelial cells.
abstract: We have studied the influence of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), the vitamin A derivative retinoic acid and the benzodiazepine diazepam on intercellular communication via established gap junctions in a monolayer of rat liver epithelial cells (RLB) at various times of incubation. Intercellular communication was measured as the transfer of [3H]hypoxanthine-derived nucleotides between RLB hypoxanthine guanine phosphoribosyl transferase+ (HPRT+) and RLB HPRT- cells. TPA only showed transient inhibition of metabolic cooperation: after 4 h of treatment, intercellular communication was reduced to about 40% of the control and longer treatments showed progressively less effect until 24 h of treatment, when no difference was seen between TPA-treated and control preparations. Retinoic acid was a more effective inhibitor: both 3 X 10(-6) M applied for 24 h and 10(-4) M applied for 6.5 h, caused a 50% inhibition of label transfer. The junctional communication could only be blocked at very high concentrations (5 X 10(-4) M) in short-exposure experiments, but this is possibly a consequence of non-specific effects on the cell membrane. When the incubation time was 24 h, a considerable portion of the gap junctions appeared to persist in the 'open' state. Diazepam showed no significant inhibitory effect in the experiments performed.
mesh_terms: D000818:Animals; D002450:Cell Communication / Q000187:drug effects*; D002460:Cell Line; D003975:Diazepam / Q000494:pharmacology*; D004848:Epithelium; D007042:Hypoxanthines / Q000378:metabolism; D007365:Intercellular Junctions / Q000187:drug effects / Q000378:metabolism; D008099:Liver; D008114:Liver Neoplasms, Experimental; D010704:Phorbols / Q000494:pharmacology*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D007042:Hypoxanthines; D010704:Phorbols; D014212:Tretinoin; D013755:Tetradecanoylphorbol Acetate; D003975:Diazepam