TGF‐β1 Effect on Cortical Collecting Duct Cells

Abstract

ENaC in collecting duct (CD) cells is involved in the regulation of Na balance and blood pressure. Prostasin, an endogenous protease, has been shown to activate ENaC, which can be mimicked by trypsin. Basolateral (BL) TGF‐β1 has been shown to inhibit Na current (Ieq), mRNA expression of prostasin and ENaC subunits. The purpose of this study was to characterize the CD response to TGF‐β1, in particular the involvement of proteolytic processes and the paracellular pathway. M‐1 cells were studied on permeable supports. The activity of secreted serine proteases was measured by an amidolytic assay. BL TGF‐β1 inhibited Ieq in the range of 2–40 ng/ml. The most marked effect was observed at concentrations ≥20 ng/ml, with >60% inhibition at 24 hours. However, transepithelial resistance Rte also decreased significantly after 2 hours, and to > 50% inhibition at 24 hours, an effect not expected with inhibition of ENaC only. The effects of TGF‐β1 on Ieq and Rte were not reversed by trypsin. Proteolytic activity in the apical media was not altered by TGF‐β1. In conclusion, BL TGF‐β1 significantly decreases Na transport in CD cells but also increases paracellular permeability. The lack of response to trypsin in TGF‐β1 treated cells implies that the down‐regulation of prostasin is not the major factor in the inhibition of Na current by TGF‐β1.Supported by research grants from VA and NIH.