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Calcium Permeability of Non‐ N ‐Methyl‐ D ‐Aspartate Receptor Channels in Immature Cerebellar Purkinje Cells: Studies Using Fura‐2 Microfluorometry
Author(s) -
Sorimachi Masaru
Publication year - 1993
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1993.tb03282.x
Subject(s) - kainate receptor , nmda receptor , chemistry , biophysics , agonist , calcium , cerebellum , glutamate receptor , channel blocker , voltage dependent calcium channel , nbqx , receptor , medicine , endocrinology , ampa receptor , biochemistry , biology , organic chemistry
Using fura‐2 microfluorometry, I investigated the mechanism by which non‐ N ‐methyl‐ d ‐aspartate (NMDA) receptor agonists increase the cytosolic free calcium concentration ([Ca] in ) in single cerebellar Purkinje cells isolated from 3–10‐day‐old rats. Kainate and α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate dose‐dependently increased the cytosolic free Na + concentration, which was measured using sodium‐binding benzofuran isophthalate microfluorometry, confirming the Na + influx through ion channels linked to non‐NMDA receptors. The [Ca 2+ ] increases induced by relatively lower concentrations of agonists were entirely dependent on external Ca 2+ and were reduced by removal of external Na + or by addition of a Ca 2+ channel blocker, D600. The results indicate that the non‐NMDA agonist–induced [Ca] in increase was due mainly to Ca 2+ influx through voltage‐dependent Ca 2+ channels, which were activated by a massive Na + influx. On the other hand, higher concentrations of agonists dose‐dependently increased [Ca] in under conditions in which activation of voltage‐dependent Ca 2+ channels were blocked by a combination of Na + removal with D600. These [Ca] in increases were Ca 2+ dependent and little affected by adding a competitive NMDA antagonist. Non‐NMDA agonists also stimulated influxes of Mn 2+ and Co 2+ , both of which can be monitored by quenching fura‐2 fluorescence under the same conditions. These results suggest that ion channels linked to non‐NMDA receptors on immature Purkinje cells are permeable to Ca 2+ , Mn 2+ , and Co 2+ .