Sodium-Calcium Exchanger Modulates the L-Glutamate Ca_i ²⁺ Signalling in Type-1 Cerebellar Astrocytes

Abstract

We have previously demonstrated that rat type-1 cerebellar astrocytes express a very active Na⁺/Ca²⁺ exchanger which accounts for most of the total plasma membrane Ca²⁺ fluxes and for the clearance of Ca ²⁺_i induced by physiological agonist. In this chapter, we have explored the mechanism by which the reverse Na⁺/Ca²⁺ exchange is involved in agonist-induced Ca²⁺ signalling in rat cerebellar astrocytes. Laser-scanning confocal microscopy experiments using immunofluorescence labelling of Na⁺/Ca²⁺ exchanger and RyRs demonstrated that they are highly co-localized. The most important finding presented in this chapter is that L-glutamate activates the reverse mode of the Na⁺/Ca²⁺ exchange by inducing a Na⁺ entry through the electrogenic Na⁺-glutamate co-transporter and not through the ionophoric L-glutamate receptors as confirmed by pharmacological experiments with specific blockers of ionophoric L-glutamate receptors, electrogenic glutamate transporters and the Na/Ca exchange.