Effects of lowering [Na +] o and [K +] o and of ouabain on quisqualate-induced ionic changes in area CA1 of rat hippocampal slices

Changes in extracellular ([Na +] o) and calcium ([Ca 2+] o) concentration evoked by quisqualate (Quis), applied iontophoretically, were measured in rat hippocampal slices. Following an initial decrease in [Ca 2+] o, Quis causes a post-application overshoot, which may reflect Ca 2+ extrusion from cells by the Na + Ca 2+ exchanger. To test this hypothesis, the effects of directly and indirectly reduced transmembrane Na + gradients on these Quis-induced Ca 2+ overshoots were investigated. In all cases the post-application overshoots were reduced. This suggests that the Na + Ca 2+ exchanger is involved in the production of these Quis-induced Ca 2+ overshoots which may have important implications for understanding how various types of glutamate receptors differ in their capability to trigger Ca 2+-activated processes.