PROTAMINE INCREASES THE PERMEABILITY OF CULTURED EPITHELIAL MONOLAYERS

Polycations, including protamine, have been reported to decrease the barrier integrity of cultured rat pulmonary type II epithelial monolayers. In contrast, protamine has been reported to increase the transepithelial electrical resistance of gallbladder epithelium. The present study was done using Madin Darby canine kidney epithelial cells (MDCK) to determine whether the effect of protamine on type II epithelial monolayers was species or organ specific or was dependent on the presence of nonepithelial cells and to investigate the effect of protamine on the actin cytoskeleton. Exposure of MDCK monolayers to protamine resulted in decreased transepithelial electrical resistance (R(t)), increased short-circuit current (I(sc)) across the monolayers, and increased mannitol permeability (P(mann)) of the monolayers. The decrease in R(t) and increase in I(sc) was seen only after the addition of protamine to the apical surface of the cells. The importance of charge in this action was supported by the fact that exposure of the monolayer to the polycation poly-L-lysine also resulted in increased P(mann), and both the decreased R(t) and increased P(mann) seen after the addition of protamine were prevented if the monolayers were exposed in the presence of the polyanions heparin or sulfated dextran. The increase in P(mann) appeared to be the result of increased permeability in the paracellular pathway, because increased mannitol uptake by the cells represented only a fraction of the increase in P(mann). Subtle changes in the actin cytoskeleton were seen after exposure of the monolayers to protamine. These results demonstrate that the polycation protamine can directly decrease the barrier integrity of a cultured epithelium and suggest that some of this effect may be the result of changes in the actin cytoskeleton. Polycations may, therefore, contribute to tissue injury by actions on epithelial cells in addition to their previously described effects on endothelial cells.