GLUTAMATE TRANSPORT MODULATION OF PARACELLULAR PERMEABILITY ACROSS LLC-PK1-F+ MONOLAYERS

The role of extracellular glutamate in modulating paracellular permeab ility was assessed in proximal tubulelike LLC-PK1-F+ cells and the rab bit kidney-derived cell line RK(13). The cells were grown to confluent monolayers on porous supports in a modified Dulbecco's modified Eagle 's medium containing 1.8 mM L-glutamine and 50 mu M L-glutamate. Chang es in paracellular permeability related to cellular glutamate uptake w ere inferred from measured transepithelial electrical resistance and L -glucose permeability. In LLC-PK1-F+ monolayers, reducing glutamate up take by blocking transport or eliminating extracellular production by inhibiting gamma-glutamyltransferase (gamma-GT) resulted in decreased electrical resistance and increased L-glucose permeability. Supplement ing gamma-GT-inhibited monolayers with 1 mM L-glutamate restored both cellular glutamate and electrical resistance. These results are consis tent with glutamate transport playing a major role in maintaining para cellular permeability in the LLC-PK1-F+ monolayers. On the other hand, in RK(13) monolayers expressing <10% of the LLC-PK1-F+'s gamma-GT act ivity, blocking their low rate of glutamate transport resulted in a mu ch smaller increase in paracellular permeability. These results are co nsistent with a role for gamma-GT and glutamate transport acting as a functional unit in the modulation of the paracellular permeability.