Ab. Garlin et al., PHARMACOLOGY OF SODIUM-DEPENDENT HIGH-AFFINITY L-[H-3]GLUTAMATE TRANSPORT IN GLIAL CULTURES, Journal of neurochemistry, 64(6), 1995, pp. 2572-2580
Pharmacological and molecular biological studies provide evidence for
subtypes of sodium-dependent high-affinity glutamate (Glu) transport i
n the mammalian CNS. At least some of these transporters appear to be
selectively expressed in different brain regions or by different cell
types. In the present study, the properties of L-[H-3]Glu transport we
re characterized using astrocyte-enriched cultures prepared from cereb
ellum and cortex. In both brain regions, the kinetic data for sodium-d
ependent transport were consistent with a single site with K-m values
of 91 +/- 17 mu M in cortical glial cells and 66 +/- 23 mu M in cerebe
llar glial cells. The capacities were 6.1 +/- 1.6 nmol/mg of protein/m
in in cortical glial cells and 8.4 +/- 0.9 nmol/mg of protein/min in c
erebellar glial cells. The potencies of similar to 40 excitatory amino
acid analogues for inhibition of sodium-dependent transport into glia
l cells prepared from cortex and cerebellum were examined, including c
ompounds that are selective inhibitors of transport in synaptosomes pr
epared from either cerebellum or cortex. Of the analogues tested, 14 i
nhibited transport activity by > 50% at 1 mM concentrations. Unlike L-
[H-3]Glu transport in synaptosomes prepared from cerebellum or cortex,
there were no large differences between the potencies of compounds fo
r inhibition of transport measured in glial cells prepared from these
two brain regions. With the exception of (2S,1'R,2'R)-2-(carboxy-cyclo
propyl)glycine and L-alpha-aminoadipate, all of the compounds examined
were similar to 10-200-fold less potent as inhibitors of L-[H-3]Glu t
ransport measured in glial cells than as inhibitors of transport measu
red in synaptosomes prepared from their respective brain regions. The
pharmacology of transport measured in these glial cells differs from t
he reported pharmacology of the cloned Glu transporters, suggesting th
e existence of additional uncloned Glu transporters or Glu transporter
subunits.