Characterization of L-alpha-aminoadipic acid transport in cultured rat astrocytes.
The mechanism of the selective gliotoxicity of L-alpha-aminoadipate (L-alpha AA) is thought to involve its entry into glia as a substrate for glutamate transporters or, alternatively, its ability to inhibit glial glutamate transport. To clarify the properties of L-alpha AA as a transport substrate, we explored the ionic dependence, kinetics and pharmacology of L-[3H] alpha AA uptake in rat cortical astrocytes. We observed two components of saturable L-alpha AA uptake, one Na(+)-dependent and the other Na(+)-independent. These components exhibited the characteristics of system X-AG, the widespread family of Na(+)-cotransporters of aspartate and glutamate, and system x-c, a Cl(-)-dependent glutamate/cystine exchanger, respectively. The K(m) value of Na(+)-dependent L-alpha AA uptake was 629 +/- 42 microM, and Vmax was 62 +/- 4 nmol.min-1.mg-1 protein, which was more than twice the capacity of Na(+)-dependent glutamate uptake. The kinetic parameters of Na(+)-dependent L-alpha AA uptake (K(m) of 20 +/- 2 microM, Vmax of 1.7 +/- 0.4 nmol.min-1.mg-1 protein did not differ from the values for Na(+)-independent glutamate uptake, indicating that L-alpha AA and glutamate are equally good substrates for system x-c.
Tsai
M J
MJ
Department of Oral and Craniofacial Biological Sciences, University of Maryland Dental School, Baltimore, USA. mtsai@ibms.sinica.edu.tw
Chang
Y F
YF
Schwarcz
R
R
Brookes
N
N
D015074:2-Aminoadipic Acid / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002021:Buffers; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D007038:Hypotonic Solutions; D007700:Kinetics; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013696:Temperature
D002021:Buffers; D002712:Chlorides; D018691:Excitatory Amino Acid Antagonists; D007038:Hypotonic Solutions; D015074:2-Aminoadipic Acid; D012964:Sodium; D011188:Potassium