Calcium permeability of non-N-methyl-D-aspartate receptor channels in immature cerebellar Purkinje cells: studies using fura-2 microfluorometry.
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 alpha-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 [Ca2+] increases induced by relatively lower concentrations of agonists were entirely dependent on external Ca2+ and were reduced by removal of external Na+ or by addition of a Ca2+ channel blocker, D600. The results indicate that the non-NMDA agonist-induced [Ca]in increase was due mainly to Ca2+ influx through voltage-dependent Ca2+ 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 Ca2+ channels were blocked by a combination of Na+ removal with D600. These [Ca]in increases were Ca2+ dependent and little affected by adding a competitive NMDA antagonist. Non-NMDA agonists also stimulated influxes of Mn2+ and Co2+, 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 Ca2+, Mn2+, and Co2+.
Sorimachi
M
M
Department of Physiology, Kagoshima University, School of Medicine, Japan.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D003035:Cobalt / Q000378:metabolism; D003592:Cytophotometry; D005456:Fluorescent Dyes; D016257:Fura-2; D005711:Gallopamil / Q000494:pharmacology; D007051:Ibotenic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007608:Kainic Acid / Q000494:pharmacology; D008345:Manganese / Q000378:metabolism; D011689:Purkinje Cells / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid
D005456:Fluorescent Dyes; D016194:Receptors, N-Methyl-D-Aspartate; D007051:Ibotenic Acid; D005711:Gallopamil; D003035:Cobalt; D008345:Manganese; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D012964:Sodium; D007608:Kainic Acid; D002118:Calcium; D016257:Fura-2