Both enantiomers of 1-aminocyclopentyl-1,3-dicarboxylate are full agonists of metabotropic glutamate receptors coupled to phospholipase C.
We tested the effects of two enantiomers of a glutamate analogue, (trans)-1-aminocyclopentyl-1,3-dicarboxylate (t-ACPD), in striatal and cerebellar neurons in primary culture, as well as in Xenopus oocytes injected with cerebellar rat RNA. In the presence of MK-801, to avoid N-methyl-D-aspartate receptor activation, and 3 microM tetrodotoxin, both enantiomers [(1R,3S)- and (1S,3R)-t-ACPD] stimulated inositol phosphate (InsP) formation both in striatal neurons after 9-11 days in vitro [EC50, 3.7 +/- 1.1 microM, three experiments, and 33 +/- 7.5 microM, three experiments; maximal stimulatory effects, 252 +/- 15%, 13 experiments, and 269 +/- 15% of basal InsP formation, 14 experiments, for (1R,3S)- and (1S,3R)-t-ACPD, respectively] and in cerebellar granule cells after 9-11 days in vitro [EC50, 50 +/- 18 microM, four experiments, and 307 +/- 92 microM, four experiments; maximal stimulatory effects, 401 +/- 71%, eight experiments, and 423 +/- 75% of basal InsP formation, eight experiments, for (1R,3S)- and (1S,3R)-t-ACPD, respectively]. These effects were not additive, indicating that both enantiomers acted at the same receptor molecule. When we monitored t-ACPD-induced increases in intracellular Ca2+ concentration ([Ca2+]i) with fura-2 ratio-imaging, we found that both enantiomers could elicit similar increase in [Ca2+]i, in the presence of 1 microM MK-801 and 3 microM tetrodotoxin; these effects were also observed in the absence of external Ca2+. Moreover, in Xenopus oocytes injected with adult rat cerebellar RNA, both drugs elicited oscillatory increases of a Ca(2+)-dependent chloride conductance, with similar efficacy, with (1R,3S)-t-ACPD being the more potent isomer. These data are in contradiction to previous reports showing that, in "immature" cerebellar neurons and adult hippocampal slices, (1S,3R)-t-ACPD was either the only active enantiomer or a full agonist of metabotropic receptors, with (1R,3S)-t-ACPD being ineffective or a partial agonist. However, performing these experiments in immature (2-3 days in vitro) striatal or cerebellar neurons, we found that only (1S,3R)-t-ACPD was active in stimulating [Ca2+]i.
Manzoni
O
O
Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France.
Prezeau
L
L
Rassendren
F A
FA
Sladeczek
F
F
Curry
K
K
Bockaert
J
J
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D003515:Cycloleucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000187:drug effects; D005260:Female; D007295:Inositol Phosphates / Q000096:biosynthesis; D007424:Intracellular Fluid / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D012313:RNA / Q000494:pharmacology; D051381:Rats; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D013237:Stereoisomerism; D013268:Stimulation, Chemical; D010738:Type C Phospholipases / Q000378:metabolism*; D014981:Xenopus
D007295:Inositol Phosphates; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D012313:RNA; D010738:Type C Phospholipases; D002118:Calcium