Pharmacological characterisation of metabotropic glutamatergic and purinergic receptors linked to Ca2+ signalling in hippocampal astrocytes.
Intracellular Ca2+ ([Ca2+]i) signals induced by metabotropic glutamate receptor (mGluR) agonists and by purinergic agonists in cultured hippocampal astrocytes were investigated using [Ca2+]-sensitive fluorophores. The mGluR agonists (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) and (R,S)-3,5-dihydroxyphenylglycine (DHPG) induced [Ca2+]i responses in 76 and 93% of the cells, respectively. The broad-spectrum mGluR antagonist (+)-alpha-methyl-4-carboxyphenylglycine (MCPG) and the mGluR1 antagonists (S)-4-carboxy-3-hydroxyphenylglycine (4C3HPG) and (S)-4-carboxyphenylglycine (4CPG) suppressed the agonist-evoked [Ca2+]i response in about 25% of the cells completely and in about 60% partially, depending on the agonist concentration employed. Together with immunohistochemical receptor localisations these results suggest the presence of at least two subpopulations of class I mGluRs recruited from the truncated splice variants of mGluR1 (mGluR 1b, 1c, 1d) and/or hitherto unknown glial-specific class I mGluRs. Of the hippocampal astrocytes 88, 92 or 83% of the cells responded with a [Ca2+]i elevation (mostly oscillations) to application of ATP, ADP, or 2-methylthio-ATP (2-MeS-ATP), respectively, whereas only 14 and 5% responded to AMP and adenosine, respectively, indicating the predominance of P2 receptors. The ATP-induced [Ca2+]i signal was suppressed by suramin. Release of Ca2+ from intracellular stores was involved in the response to ATP because the cells also exhibited [Ca2+]i elevations in Ca2+-free medium. Cells did not respond to 10 microM UTP. We conclude that the P2Y subtype represents the main [Ca2+]i-linked purinoceptor in hippocampal astrocytes. Sequential application of ATP and DHPG in Ca-free medium showed that metabotropic glutamate and purinergic receptors initiate release of Ca2+ from subsets of cyclopiazonic acid-sensitive Ca2+ stores which are partly independent.
Bernstein
M
M
Otto-von-Guericke Universität Magdeburg, Institut für Neurobiochemie, Germany.
Behnisch
T
T
Balschun
D
D
Reymann
K G
KG
Reiser
G
G
D000241:Adenosine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D058913:Purinergic Agonists; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects* / Q000502:physiology; D011983:Receptors, Purinergic / Q000502:physiology
D018690:Excitatory Amino Acid Agonists; D058913:Purinergic Agonists; D018094:Receptors, Metabotropic Glutamate; D011983:Receptors, Purinergic; D000255:Adenosine Triphosphate; D000241:Adenosine; D002118:Calcium