GLUTAMATE-RECEPTOR AGONISTS STIMULATE DIVERSE CALCIUM RESPONSES IN DIFFERENT TYPES OF CULTURED RAT CORTICAL GLIAL-CELLS

We examined the effects of different types of glutamate receptor agoni sts on the intracellular calcium concentration, ([Ca2+](j)) in culture d rat cortical glial cells. The cells in these cultures were character ized immunocytochemically using antibodies against glial fibrillary ac idic protein, A(2)B(5), and OX-42. The metabotropic glutamate receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid produced Ca 2+ mobilization from intracellular stores in all classes of cells. Ago nists at non-NMDA glutamate receptors also produced large increases in [Ca2+](j), primarily in cells of the O-2A lineage. Disruption of intr acellular Ca2+ stores with thapsigargin showed that increases in [Ca2](j) produced by activating AMPA/kainate receptors were primarily due to Ca2+ influx rather than Ca2+-induced Ca2+ release. Agonists at NMDA receptors were ineffective. Electrophysiological studies revealed tha t cells of the O-2A lineage exhibited moderate inward currents in resp onse to kainate in Na+-containing solutions, but only small inward cur rents and outward rectification in Na+-free solutions. However, in the presence of cyclothiazide, the kainate-induced currents were increase d in size and a rightward shift of the reversal potential with increas ed [Ca2+](j) could be demonstrated. Activation of cells by kainate, bu t not by depolarizing stimuli, stimulated the uptake of Co2+. Polymera se 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 re ceptor agonists in the O-2A lineage population is discussed. It is con sidered 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.