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

We have investigated whether the intracellular calcium concentration ([Ca(2+)](i)) oscillations induced in astrocytes using the metabotropic glutamate-receptor agonist, (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD) are Ca(2+)-dependent, using three different Ca(2+) indicators with different affinities for Ca(2+). 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 [Ca(2+)](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 [Ca(2+)](i). The same small transient [Ca(2+)](i) increase was seen in cells loaded with both fura-2FF and BAPTA, a Ca(2+) chelator (K(d): 135 nM). These findings indicate the involvement of [Ca(2+)](i)-dependent regulatory mechanisms in the induction of the t-ACPD-induced oscillatory change in the [Ca(2+)](i) in astrocytes.