Short‐ and Long‐term Regulation of Intestinal Na+/H+ exchange by TLR4 in intestinal epithelial cells

Abstract

The ability of recognizing microbiological infections is largely dependent on toll‐like receptors (TLR). TLR4 is expressed in the cell membrane and is activated by bacterial lipopolysaccharide, one of components of the outer membrane of Gram‐negative bacteria.AimsTo evaluate the effect of TLR4 activation by Monophosphoryl Lipid A (MPLA) on Na+/H+ exchanger (NHE) activity in T84 cells as well the signal transduction set in motion.Material and methodsNHE activity and kinetics were measured using fluorimetric assays and protein expression was determined by western blot analysis.ResultsShort‐ and long‐term MPLA (0.01 to 50 µg/ml) exposure induced an NHE1 concentration dependent inhibition (st ‐4.9±5 to ‐25.2±5 %; lt ‐3.9± to ‐31.9±4 %) without any effect over NHE membrane protein expression. The cell signal triggered AC3, PKA, PLC and PKC signal molecules. Long‐term exposure induced changes in NHE activity but affecting different NHE isoforms depending on MPLA concentration, lower MPLA induced NHE3 inhibition and higher MPLA concentrations induced NHE1 inhibition. In both cases AC3, PKA, PLC and PKC are involved. That is, the final effector of NHE1 was PCK and for NHE3 was PKA. MPLA induced an impaired recover of pHi and consequent acidification of intracellular media.ConclusionsActivation of TLR4 exerts marked inhibition of both NHE1 and NHE3 activity in intestinal epithelial cells. Transduction mechanisms set into motion during short‐ and long‐term TLR4‐mediated inhibition of NHE1 activity involves AC and PKA. However, short‐ and long‐term TLR4 activation might use different signalling pathways.