title: Maturation-dependent reduced responsiveness of intracellular free Ca2+ ions to repeated stimulation by N-methyl-D-aspartate in cultured rat cortical neurons.
abstract: In contrast to other ionotropic glutamate receptors, N-methyl-d-aspartate (NMDA) receptor channels are rather stable after the simulation. Brief exposure to NMDA at 50 microM rapidly increased the fluorescence intensity for increased intracellular free Ca(2+) levels in a reversible- and concentration-dependent manner in rat cortical neurons cultured for 3-15 days in vitro (DIV), while EC(50) values were significantly decreased in proportion to cellular maturation from 3 to 15 DIV. Although a constant increase was persistently seen in the fluorescence throughout the sustained exposure to NMDA for 60 min irrespective of the cell maturation from 3 to 15 DIV, the second brief exposure for 5 min resulted in a less efficient increase in the fluorescence than that found after the first brief exposure for 5 min in a manner dependent on intervals between the two repetitive brief exposures. In vitro maturation significantly shortened the interval required for the reduced responsiveness to the second brief exposure, while in immature neurons prolonged intervals were required for the reduced responsiveness to the second brief exposure to NMDA. Moreover, brief exposure to NMDA led to a marked decrease in immunoreactivity to extracellular loop of NR1 subunit in cultured neurons not permeabilized in proportion to the time after washing. These results suggest that cellular maturation would facilitate the desensitization process to repeated stimulation by NMDA, without markedly affecting that to sustained stimulation, through a mechanism related to the decreased number of NMDA receptors expressed at cell surfaces in cultured rat cortical neurons.
authors.affiliation: Laboratory of Molecular Pharmacology, Division of Pharmaceutical Sciences, Kanazawa University Graduate School of Natural Science and Technology, Kakuma-machi, Ishikawa 920-1192, Japan.
authors.forename: Noritaka
authors.initials: N
authors.lastname: Nakamichi
authors.forename: Yukio
authors.initials: Y
authors.lastname: Yoneda
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D049108:Cell Enlargement / Q000187:drug effects; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D016202:N-Methylaspartate / Q000008:administration & dosage* / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D016202:N-Methylaspartate