Activation of the amiloride-sensitive epithelial sodium channel by the serine protease mCAP1 expressed in a mouse cortical collecting duct cell line

This study examines whether serine proteases can activate the amiloride-sen sitive sodium channel (ENaC) in mammalian kidney epithelial cells. The tran sepithelial sodium transport assessed by amiloride-sensitive short-circuit current appears to be sensitive to aprotinin, a protease inhibitor in a mou se cortical collecting duct cell line (mpkCCD(c14)). This result indicated that serine proteases may be implicated in the regulation of ENaC-mediated sodium transport. Using degenerated oligonucleotides to a previously isolat ed serine protease from Xenopus, xCAP1 (channel activating protease), a nov el full-length serine protease (mCAP1), has been isolated and characterized . RNA analysis showed a broad pattern of expression in tissues (kidney, lun g, colon, and salivary glands) expressing ENaC. Reverse transcription-PCR e xperiments also showed that mCAP1 was abundantly expressed in proximal tubu le cells and was also expressed in intact and cultured collecting duct cell s. Coexpression of the Xenopus, rat, or human alpha-, beta-, and gamma-ENaC subunits in Xenopus oocytes also showed that mCAP1 induces a significant i ncrease in ENaC-mediated current accompanied by a decrease of channel molec ules at the cell surface. It is proposed that this novel mouse channel acti vating protease may act as a regulator of ENaC within the kidney.