Extracellular glutamate flux regulates intracellular glutaminase activity in llc-pk1-f+ cells. Welbourne, T. C., and X. Mu. Department of Physiology, LSUMC, Shreveport, LA 71130
APStracts 2:0052C, 1995.
The role of extracellular glutamate flux in regulating intracellular glutaminase activity was assessed in confluent monolayers of proximal tubule -like LLC-PK-F+ cells grown on porous supports. Glutamate is a well known inhibitor of phosphate dependent glutaminase, PDG. We hypothesized that by restricting the flux of glutamate from the extracellular media, cellular level would fall effecting deinhibition of the cellular glutaminase activity. To test this, cellular glutamate uptake and extracellular production were inhibited for 18h by adding D-aspartate, 10mM, or acivicin, 0.7mM, to both apical and basal media. Inhibiting glutamate flux depressed cellular glutamate content 43% and 41% respectively. Intracellular relative glutaminase activity monitored as the breakdown of 14C-radiolabeled glutamine to glutamate measured over 60 seconds in the presence of D-aspartate or acivicin showed a 2 to 2.5-fold increase with the fall in cellular glutamate. Interestingly, enhanced glutamine uptake after PDG deinhibition was predominantly expressed on the basal surface. Indeed, measuring glutamine utilization following _-GT inhibition over the entire 18h time course revealed inhibition at the apical surface but relative enhancement of uptake at the basal surface. The increased intracellular glutaminase pathway was also reflected in increased alanine production measured over the 18h time course despite the reduction in overall glutamine utilization. These results point to a major role for extracellular glutamate fluxes in regulating cellular glutamine metabolism and suggest that the intracellular pathway may be suppressed under these conditions. 

Received 17 August 1994; accepted in final form 12 December 1994
APS Manuscript Number C0490-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.