Carbon tetrachloride at hepatotoxic levels blocks reversibly gap junctions between rat hepatocytes

A role for the extracellular matrix in retinal neurogenesis in vitro

The germinal neuroepithelial cells that give rise to the majority of neurons in the vertebrate central nervous system are in contact with the basement membrane that surrounds the neural tube from the very earliest stages. The effect of removing this basement membrane on the organization and proliferative potential of these cells was examined in a new slice culture preparation of developing Rana tadpole retina. The results indicate that the germinal neuroepithelium, like other epithelial tissues, requires contact with a basement membrane for the maintenance of its structure and a normal degree of cell proliferation.

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.

Concentration/response effect of 2,2', 4,4', 5,5'-hexabromobiphenyl on cell-cell communication in vitro: assessment by fluorescence redistribution after photobleaching ("FRAP")

Inhibition of gap junction-mediated cell-cell communication might be a mechanism for several types of cellular dysfunctions, including tumor promotion. Although many different assays have been designed to measure gap junction-mediated intercellular communication, we applied a new technique, termed Fluorescence Redistribution After Photobleaching ("FRAP"), to assess the ability of a known tumor promoter, 2,2', 4,4', 5,5'-hexabromobiphenyl (245-HBB), to inhibit cell-cell communication in a concentration-dependent manner. WB-F344 (rat epithelial) cells were plated at low density, exposed to noncytotoxic concentrations of 1, 5, or 20 micrograms 245-HBB/ml medium, and stained with 6-carboxyfluorescein diacetate. Single cells in pairs or clusters of touching cells in each exposure group were examined with FRAP. The results revealed an inverse correlation between the degree of fluorescence redistribution in photobleached cells and the concentration of 245-HBB. Therefore, FRAP appears to be a sensitive and rapid technique for determining complete or partial inhibition of chemically induced intercellular communication in vitro. These results also provide further evidence for the ability of 245-HBB to inhibit gap junction-mediated cell-cell communication in a concentration-dependent manner.

Anchored cell analysis/sorting coupled with the scrape-loading/dye-transfer technique to quantify inhibition of gap-junctional intercellular communication in WB-F344 cells by 2,2',4,4',5,5'-hexabromobiphenyl

Inhibition of intercellular communication has been hypothesized to play a role in tumor promotion. The compound 2,2',4,4',5,5'-hexabromobiphenyl (245-HBB) is a tumor promoter in vivo and blocks intercellular communication in vitro. The scrape-loading/dye-transfer (SL/DT) assay was used to assess this in vitro effect at varying concentrations of 245-HBB. The SL/DT technique is based on the intracellular loading of a fluorescent dye, lucifer yellow (LY), and monitoring its transfer into adjacent cells via patent gap junctions. Confluent WB-F344 (rat epithelial) cells were exposed to various noncytolethal concentrations of 245-HBB. Transfer of LY was then quantified with anchored cell analysis/sorting (ACAS 470, Meridian Instruments, Okemos, Mich.). The results indicate an inverse correlation between the degree of fluorescence in secondary LY-recipient cells and the treatment concentration. The coupling of these two new methods of cellular biology provided rapid quantitative analysis of dye transfer in measuring the concentration/response of modulation of gap-junctional permeability in cultured cells.

Loss of intercellular junctional communication correlates with metastatic potential in mammary adenocarcinoma cells

A series of rat 13762NF mammary adenocarcinoma cell sublines and clones of various spontaneous pulmonary metastatic potentials from the mammary fat pads of syngeneic rats were examined for their intercellular junctional communication. Using the scrape-loading dye-transfer technique to introduce Lucifer yellow (Mr 457) into cells, we measured the abilities of 13762NF cells to transfer dye to adjacent cells. There was an excellent correlation between loss of Lucifer yellow dye transfer and spontaneous metastatic potential (average total volume of lung metastases inversely correlated to % cells coupled, r = 0.93; average total number of lung metastases inversely correlated to % cells coupled, r = 0.91). The data suggest that high metastatic potentials are closely correlated with loss of intercellular junctional communication in these malignant mammary tumor cells.