Journal of Neuroscience, Vol 14, 1879-1891, Copyright © 1994 by Society for Neuroscience
Glutamate receptor agonists stimulate diverse calcium responses in different types of cultured rat cortical glial cells
JA Holzwarth, SJ Gibbons, JR Brorson, LH Philipson and RJ Miller
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.
We examined the effects of different types of glutamate receptor agonists
on the intracellular calcium concentration, ([Ca2+]i), in cultured rat
cortical glial cells. The cells in these cultures were characterized
immunocytochemically using antibodies against glial fibrillary acidic
protein, A2B5, and OX-42. The metabotropic glutamate receptor agonist
(1S,3R)-1-aminocyclopentane-1,3- dicarboxylic acid produced Ca2+
mobilization from intracellular stores in all classes of cells. Agonists at
non-NMDA glutamate receptors also produced large increases in [Ca2+]i,
primarily in cells of the O-2A lineage. Disruption of intracellular Ca2+
stores with thapsigargin showed that increases in [Ca2+]i produced by
activating AMPA/kainate receptors were primarily due to Ca2+ influx rather
than Ca(2+)-induced Ca2+ release. Agonists at NMDA receptors were
ineffective. Electrophysiological studies revealed that cells of the O-2A
lineage exhibited moderate inward currents in response to kainate in
Na(+)-containing solutions, but only small inward currents and outward
rectification in Na(+)-free solutions. However, in the presence of
cyclothiazide, the kainate- induced currents were increased in size and a
rightward shift of the reversal potential with increased [Ca2+]o could be
demonstrated. Activation of cells by kainate, but not by depolarizing
stimuli, stimulated the uptake of Co2+. Polymerase chain reaction studies
showed that the glutamate receptor subunits GluR1-4 and GluR6 were all
expressed in these cultures, but GluR5 was absent. The nature of the Ca2+
uptake pathway activated by non-NMDA receptor agonists in the O-2A lineage
population is discussed. It is considered most likely that the O-2A lineage
cells express both non-NMDA receptors that are relatively impermeable to
divalent cations, as well as a smaller population that are Ca2+ permeable.
