Epithelial Na+ channels are activated by laminar shear stress

The degenerin/epithelial Na+ channel (ENaC) superfamily is a group of structurally related ion channels that are involved in diverse biological processes, including responses to mechanical stimuli. In renal cortical collecting ducts, changes in rates of perfusion affect Na+ reabsorption through an amiloride-sensitive pathway, suggesting that ENaC may be a mechanosensitive channel. In this study, we examined whether ENaC expressed in oocytes is regulated by laminar shear stress (LSS). A 1.8-mm (internal diameter) perfusion pipette was placed within 0.5-1.0 mm of the oocyte to provide laminar flow across the oocyte surface. LSS induced a dose-dependent and reversible increase in benzamil-sensitive whole cell Na+ currents in oocytes expressing alphabetagamma ENaC. The half-time for activation by LSS was approximately 5 s. Repetitive stimulation by LSS of oocytes expressing ENaC was associated with a reduction in the response to LSS. Oocytes expressing alphabetaS518Kgamma, a pore region mutant with a high open probability, were insensitive to LSS. We demonstrated previously that channels with a Cys residue introduced at position alphaSer-580 had a low open probability, but, following modification by [2-(trimethylammonium)ethyl]methanethiosulfonate bromide (MTSET), channels exhibited a high open probability. Oocytes expressing alphaS580Cbetagamma ENaC respond to LSS similar to wild type; however, covalent modification by MTSET largely eliminated the response to LSS. Our results suggest that shear stress activates ENaC by modifying the gating properties of the channel.