Ca²⁺-Dependent Induction of Intracellular Ca²⁺ Oscillation in Hippocampal Astrocytes During Metabotropic Glutamate Receptor Activation

Abstract

We have investigated whether the intracellular calcium concentration ([Ca²⁺]_i) oscillations induced in astrocytes using the metabotropic glutamate-receptor agonist, (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD) are Ca²⁺-dependent, using three different Ca²⁺ indicators with different affinities for Ca²⁺. When rat hippocampal cells in culture were loaded with fura-2 (K_d: 145 nM), two-thirds of the cells showed obvious oscillatory increase in [Ca ²⁺]_i during t-ACPD-administration. Those cells were identified as astrocytes by immuno-histochemistry in our previous paper. In cells loaded with fura-2FF (K_d: 25,000 nM), a similar percentage of t-ACPD-responsive cells showed oscillatory [Ca²⁺]_i changes. However, in cells loaded with quin-2 (K_d: 60 nM), t-ACPD induced no oscillatory responses, but some cells showed a small transient increase in the [Ca²⁺]_i. The same small transient [Ca²⁺]_i increase was seen in cells loaded with both fura-2FF and BAPTA, a Ca²⁺ chelator (K_d: 135 nM). These findings indicate the involvement of [Ca²⁺]_i-dependent regulatory mechanisms in the induction of the t-ACPD-induced oscillatory change in the [Ca²⁺]_i in astrocytes.