Opposite regulation of transepithelial electrical resistance and paracellular permeability by Rho in Madin-Darby canine kidney cells

Small GTPase Rho has been thought to be important for the formation and the maintenance of tight junction in epithelial cells, but the role of Rho in the regulation of barrier function of tight junction is not web understood. We here examined whether Rho was involved in the barrier function of tight junction in Madin-Darby canine kidney (MDCK) cells. The activation of prostaglandin EP3 beta receptor, coupled to a Rho activation pathway, induced the increase in transepithelial electrical resistance (TER) but the increase in paracellular flux of mannitol in the preformed monolayer of the MDCK cells expressing the EP3 beta receptor. This effect of the EP3 receptor was mimicked by the expression of constitutively active RhoA but not by active Rad in MDCK cells, using an isopropyl-beta-D-thiogalactoside-inducible expression system. On the other hand, the activation of EP3 beta receptor suppressed the elevation of TER and the decrease in paracellular mannitol flux during Ca2+ switch-induced tight junction formation, whereas the expression of active RhoA or Rad did not apparently affect the TER development in the Ca2+ switch. These results demonstrate that the EP3 receptor and active RhoA regulate permeabilities of ionic and nonionic molecules in opposite directions in the preformed monolayer, and the EP3 receptor suppresses the elevation of TER during the tight junction formation.