Plasma membrane depolarization‐induced ERK activation: role in regulating paracellular permeability of the proximal tubular epithelium

Abstract

Both physiological and pathological conditions, including apical ion transport, hypoxia, oxidative stress, and ATP depletion can alter the membrane potential of epithelial cells. We have previously shown that membrane depolarization induces Rho‐Rho kinase (ROK) mediated phosphorylation of myosin light chain (MLC) in proximal tubule epithelial cells and elevates paracellular permeability. Here we show that the permeability increase was absent in cells stably expressing a non‐phosphorylatable, dominant negative MLC. Depolarization, elicited by high extracellular [K+],– or ouabain, an inhibitor of the Na+/K+ ATPase, also activated the Ras‐Raf‐MEK‐ERK pathway. ERK activation was fast, reversible and independent of intracellular Ca2+. Immunofluorescent staining revealed that ERK translocates to the cell periphery. The MEK inhibitor PD98059 reduced the depolarization‐induced rise in paracellular permeability. Interestingly, PD98059 also mitigated the depolarization‐induced MLC phosphorylation, raising the possibility that ERK affects paracellular permeability by contributing to increased contractility.In summary, our data suggest that cell contractility, regulated by the Rho‐ROK and the Ras‐ERK pathway might play a key role in epithelial barrier dysfunction caused by sustained depolarization.Support: NSERC, Banting Foundation and Kidney Foundation of Canada.