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 (Kd: 145 nM), two-thirds of the cells showed obvious oscillatory increase in [Ca2+]i during t-ACPD-administration. Those cells were identified as astrocytes by immunohistochemistry in our previous paper. In cells loaded with fura-2FF (Kd: 25,000 nM), a similar percentage of t-ACPD-responsive cells showed oscillatory [Ca2+]i changes. However, in cells loaded with quin-2 (Kd: 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 (Kd: 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. Keywords:: astrocyte, calcium oscillation, metabotropic glutamate receptor, calcium indicator, cell culture