Astrocyte mGlu(2/3)-mediated cAMP potentiation is calcium sensitive: studies in murine neuronal and astrocyte cultures.
Signal transduction mechanisms of group II metabotropic glutamate receptors (mGlu(2/3)) remains a matter of some controversy, therefore we sought to gain new insights into its regulation by studying cAMP production in cultured neurons and astrocytes, and by examining inter-relationships of mGlu(2/3)-induced signalling with cellular calcium and various signalling cascades. mGlu(2/3) agonists 2R,4R-4-aminopyrrolidine-2,4-dicarboxylic acid (2R,4R-APDC) and (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylic acid (LY379268) inhibited 10 microM forskolin-stimulated production of cAMP in murine cortical neurons, striatal neurons and forebrain astrocytes in the absence of extracellular Ca(2+). These agonists potentiated cAMP production in the presence of 1.8 mM Ca(2+) in astrocytes only. This potentiation was dependent on the extracellular Ca(2+) concentration (0.001-10 mM) and inhibited by the mGlu(2/3) antagonist LY341495 (1 microM), adenosine deaminase (1 U/ml) and the adenosine A(2A) receptor antagonist ZM241385 (1 microM). Pre-incubation with the phospholipase C (PLC) inhibitor U73122 (10 microM), L-type Ca(2+)-channel blockers nifedipine (1 microM) and nimodipine (1 microM), the calmodulin kinase II (CaMKII) inhibitor KN-62 (10 microM) or pertussis toxin (100 ng/ml) inhibited this potentiation. In the absence of 1.8 mM Ca(2+), thapsigargin (1 microM) facilitated the potentiation of cAMP production. Measurement of the Ca(2+)-binding dye Fluo-3/AM showed that, compared to Ca(2+)-free conditions, thapsigargin and 1.8 mM Ca(2+) elevated [Ca(2+)](i) in astrocytes; the latter effect being prevented by L-type Ca(2+)-channel blockers. Potentiation of cAMP production was also demonstrated when astrocytes were stimulated with the beta-adrenoceptor agonist isoprenaline (10 microM) in the presence of 1.8 mM Ca(2+), but not with the adenosine agonist NECA (10 microM) or the group I mGlu receptor agonist DHPG (100 microM). BaCl(2) (1.8 mM) in place of Ca(2+) did not facilitate forskolin-stimulated mGlu(2/3)-potentiation of cAMP. In short, this study in astrocytes demonstrates that under physiological Ca(2+) and adenylate cyclase stimulation an elevation of cAMP production is achieved that is mediated by PLC/IP(3)- and CaMKII-dependent pathways and results in the release of endogenous adenosine which acts at G(s) protein-coupled A(2A) receptors. These findings provide new insights into mGlu(2/3) signalling in astrocytes versus neurons, and which could determine the functional phenotypy of astrocytes under physiological and pathological conditions.
Moldrich
Randal X
RX
Department of Pharmacology, Monash University, Melbourne, Victoria 3800, Australia.
Apricó
Karina
K
Diwakarla
Shanti
S
O'Shea
Ross D
RD
Beart
Philip M
PM
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004622:Embryo, Mammalian; D051379:Mice; D008954:Models, Biological; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000502:physiology*
D018094:Receptors, Metabotropic Glutamate; C108822:metabotropic glutamate receptor 2; C102718:metabotropic glutamate receptor 3; D000242:Cyclic AMP; D002118:Calcium