The phorbol ester, TPA, increases transepithelial epidermal growth factor flux

Exposure of cultured kidney epithelial (LLC-PK1) cell sheets to 10(-7) M TPA, a potent tumor promoter and activator of protein kinase C, initiates within minutes a drop in the transepithelial voltage across these sheets. This fall in potential difference correlates with an over 40-fold increase in the transepithelial flux of 1 mM D-mannitol, suggesting that the intercellular junctions have become leaky. Dual labeling experiments with 1 mM D-14C]mannitol and 10 nM 125I-EGF show that after promoter treatment, a 7-fold increase in net 125I flux accompanies the increase in mannitol flux. Gel filtration and gel electrophoresis indicate that for control cell sheets only 15% of the transited 125I is actually EGF, whereas with TPA-treated cell sheets, 60% of the 125I which passed across is EGF. These percentages permitted determination of actual EGF flux values, and show that TPA treatment engenders a 35-fold increase in transepithelial EGF flux. Diacylglycerols also increase the junctional permeability of these cells, thereby suggesting the involvement of protein kinase C.