The rapid L- and D-aspartate uptake in cultured astrocytes.
Astrocytes in primary culture possess a rapid L-aspartate saturable transport system (K(m) = 93 microM; V(max) = 81 nmol/min/mg protein), which shows certain stereospecificity since V(max) was 36% lower for D-aspartate uptake. These are values obtained at short incubation time (15 seconds), to obtain approximate initial rate conditions. Metabolic energy inhibitors, rotenone and iodoacetate very potently inhibited the L- and D-aspartate uptake processes, indicating that the transport process is an active one. However, the accumulation of L-aspartate was "enhanced" by inhibitors of L-aspartate metabolism, such as the aspartate aminotransferase inhibitor, aminooxyacetate and L-methionine sulfoximine, an inhibitor of glutamine synthetase, whereas D-aspartate (a non-metabolizable analog of L-aspartate) uptake was not affected. The accumulated levels of L-aspartate in the presence of aminooxyacetate were similar to the levels of D-aspartate. These effects of L-aspartate metabolic inhibitors, suggest that due to metabolism of the the L-aspartate, short incubation time (eg., 15 seconds) is necessary to measure the initial rate of L-aspartate uptake, in order to obtain the "true" kinetic parameters.
Bender
A S
AS
Department of Pharmacology and Toxicology, College of Pharmacy, University of Utah, Salt Lake City 84112, USA.
Woodbury
D M
DM
White
H S
HS
D000625:Aminooxyacetic Acid / Q000378:metabolism; D000818:Animals; D001219:Aspartate Aminotransferases / Q000037:antagonists & inhibitors; D001224:Aspartic Acid / Q000493:pharmacokinetics*; D001253:Astrocytes / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002478:Cells, Cultured; D004734:Energy Metabolism / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors; D007461:Iodoacetates / Q000494:pharmacology; D019807:Iodoacetic Acid; D008717:Methionine Sulfoximine / Q000378:metabolism; D051379:Mice; D012402:Rotenone / Q000494:pharmacology; D013237:Stereoisomerism; D013997:Time Factors
D004791:Enzyme Inhibitors; D007461:Iodoacetates; D012402:Rotenone; D000625:Aminooxyacetic Acid; D008717:Methionine Sulfoximine; D001224:Aspartic Acid; D001219:Aspartate Aminotransferases; D005974:Glutamate-Ammonia Ligase; D019807:Iodoacetic Acid