title: Modulation of muscarinic cholinoceptor-stimulated inositol 1,4,5-trisphosphate accumulation by N-methyl-D-aspartate in neonatal rat cerebral cortex.
abstract: The mechanisms by which N-methyl-D-aspartate (NMDA) receptor activation can modulate muscarinic receptor-stimulated phosphoinositide turnover have been studied in neonatal rat cerebral cortex slices. A maximally effective concentration of carbachol (1 mM) caused a large stimulation of both total [3H]inositol phosphate ([3H]InsPx) accumulation (30-40-fold over basal levels after 15 min in the presence of 5 mM LiCl) and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] mass accumulation (consisting of a rapid peak increase of about 8-10-fold within 15 sec followed by a sustained plateau rise of 4-5-fold which persisted for > 10 min). Low concentrations of NMDA enhanced carbachol-stimulated [3H]InsPx and Ins(1,4,5)P3 accumulations with a maximal effect being observed at 10 microM NMDA. However, at higher concentrations of NMDA (30-300 microM) a dramatic inhibition of these indices of phosphoinositide turnover was observed. Time-course studies demonstrated that NMDA (100 microM) caused a significant enhancement of the initial increases in [3H]InsPx and Ins(1,4,5)P3 accumulations stimulated by carbachol, with the profound inhibitory effects becoming evident at longer incubation times. The modulatory effects of NMDA were antagonized by D-2-amino-5-phosphonopentanoate and MK-801. Reducing extracellular calcium concentration ([Ca2+]e) to the low micromolar range decreased basal Ins(1,4,5)P3 accumulation and attenuated the response to carbachol. Under these conditions NMDA (10-100 microM) caused only a potentiation of agonist-stimulated Ins(1,4,5)P3 accumulation. Under control conditions ([Ca2+]e = 1.3 mM), addition of MK-801 (1 microM) 10 min after carbachol + 100 microM NMDA challenge failed to reverse the inhibitory effect of NMDA on carbachol-stimulated [3H]InsPx accumulation. Furthermore, pre-incubation of cerebral cortex slices with 100 microM NMDA for 15 min (followed by extensive washing of slices to remove NMDA) dramatically decreased [3H]inositol incorporation into the cellular inositol phospholipid fraction and decreased basal and carbachol-stimulated Ins(1,4,5)P3 mass accumulations. We conclude that the enhancement of agonist-stimulated phosphoinositide turnover seen at concentrations of NMDA up to 10 microM may be due to Ca2+ entry and Ca2+ facilitation of phosphoinositide-specific phospholipase C activity. In contrast, the inhibitory effect of high concentrations of NMDA on agonist-stimulated phosphoinositide turnover may be due to progressive, irreversible and, at least in part, Ca(2+)-dependent damage to the cell populations in the slice preparation responding to muscarinic-receptor stimulation.
authors.affiliation: Department of Cell Physiology and Pharmacology, University of Leicester, U.K.
authors.forename: R A
authors.initials: RA
authors.lastname: Challis
authors.forename: R
authors.initials: R
authors.lastname: Mistry
authors.forename: D W
authors.initials: DW
authors.lastname: Gray
authors.forename: S R
authors.initials: SR
authors.lastname: Nahorski
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D016291:Dizocilpine Maleate / Q000494:pharmacology; D005260:Female; D005998:Glycine / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000187:drug effects*
chemical_list: D011976:Receptors, Muscarinic; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D015763:2-Amino-5-phosphonovalerate; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D008274:Magnesium; D005998:Glycine