Glutamate receptor‐linked changes in membrane potential and intracellular Ca2+ in primary rat astrocytes

Abstract

Kainate-, quisqualate- and glutamate-induced depolarization and mobilization of intracellular Ca²⁺ was determined in primary cultured astrocytes using the fluorescent probes DiBa-C₄-(3) and fura-2, respectively. All three receptor agonists depolarized the cells in a Na⁺-dependent manner and increased the intracellular Ca²⁺ concentration. The glutamate- and quisqualate-induced increase in cytosolic Ca²⁺ was only partially inhibited by removal of extracellular Ca²⁺, whereas the response to kainate was totally dependent on extracellular Ca²⁺. The mechanisms for depolarization and increases in cytosolic Ca²⁺ appeared to be independent of each other, as extracellular Ca²⁺ removal or intracellular Ca²⁺ buffering with entrapped BAPTA did not affect the depolarization. Removal of extracellular Na⁺ did not affect the agonist-induced increase in Ca²⁺. If quisqualate was added after kainate, the cells were hyperpolarized in a Ca²⁺- and K⁺-dependent manner. This could be due to effects on a Ca²⁺-dependent K⁺ channel, the effects of which are normally hidden by the greater effect on Na⁺ channels as a response to quisqualate.