Inhibition by trypsin of the high-affinity acidic amino acid transport system in C6 glioma cells.
The high-affinity uptake of the acidic amino acid D-aspartate was inhibited in a dose- and time-dependent manner, when C6 cells were exposed to trypsin. The protease decreased the maximal velocity for uptake but not its Km, consistent with a reduction in the number of competent carriers at the plasma membrane. Cellular energy production and [K+]i were unaffected, indicating that the transporter itself was the site of trypsin action. Maximum inhibition of uptake was 50%, which suggests the presence of a heterogeneous population of transporters, only half of which is sensitive to trypsin. These results support our earlier postulate that in glial cells, the high-affinity transporter for acidic amino acids is a transmembrane protein, part of which extends into the external environment.
Department of Pathology, University of Bristol, U.K.
J
J
Deas
I A
IA
Silver
M
M
Erecińska
D000818:Animals; D001224:Aspartic Acid / Q000493:pharmacokinetics*; D004734:Energy Metabolism / Q000187:drug effects; D005910:Glioma; D051381:Rats; D014357:Trypsin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism*
D001224:Aspartic Acid; D014357:Trypsin