Transepithelial paracellular leakiness induced by chronic phorbol ester exposure correlates with polyp-like foci and redistribution of protein kinase C-alpha.

Although exposure of LLC-PK1 epithelial cell sheets to phorbol esters (TPA) causes a near immediate and total decrease of transepithelial electrical resistance (TER), continuation of exposure for 3 to 4 days results in a tachyphylactic response as TER begins to return to control levels. Recovery of TER is maximal by 5 to 6 days, but reaches only 70 to 80% of control level. A reciprocal change in the transepithelial flux of D-mannitol indicates that the TER decrease is indicative of an increase in tight junction permeability.

Chronic exposure of LLC-PK1 epithelia to the phorbol ester TPA produces polyp-like foci with leaky tight junctions and altered protein kinase C-alpha expression and localization.

Acute exposure (up to 4 h) of LLC-PK1 epithelial cell sheets to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) causes a rapid decrease of transepithelial electrical resistance (TER) to less than 15% of initial value. As the TPA exposure period is continued by chronically passaging cells in the presence of TPA, TER begins to recover. By 6 weeks of exposure, TER recovers to almost 50% of its initial value, suggesting that tight junctions (TJs) are recovering barrier function even in the continued presence of TPA.

Cell division does not increase transepithelial permeability of LLC-PK1 cell sheets.

The transepithelial electrical resistance (TER) across LLC-PK1 cell sheets is unstable for several days postseeding, even when the cells are trypsinized from a previously confluent culture and replated at confluent density. We therefore followed the TER of LLC-PK1 cells plated at confluent density to elucidate characteristics of the TER fluctuations after plating of the cells. Control cultures reached a maximum TER of 1800 omega.

Regulation of hexose transport in BALB/c 3T3 preadipose cells: effects of glucose concentration and 12-O-tetradecanoylphorbol-13-acetate.

Like many cell types in culture, both undifferentiated and differentiated BALB/c 3T3 preadipose cells respond to glucose deprivation with an increased uptake of 2-deoxy-D-glucose (deoxyglucose) and 3-O-methyl-D-glucose (methylglucose). Glucose readdition to glucose-deprived cultures resulted in a prompt fall in uptake activity; in undifferentiated cells, a half-maximally effective concentration of glucose was approximately 0.5 mM, while 0.

Effects of tumor-promoting phorbol diesters on neoplastic progression of Syrian hamster embryo cells.

The progression of normal Syrian hamster embryo cells to a neoplastic phenotype after treatment with a chemical carcinogen and continuous exposure to phorbol ester tumor promoters was studied in cell culture. Tumor promoters were able to rescue cell lines derived from individual carcinogen-treated colonies from a program of cellular senescence. In general, these cell lines did not grow in soft-agar medium or produce tumors in newborn hamsters at early passages but acquired these properties at later passages.