Fluorescence measurement of changes in intracellular calcium induced by excitatory amino acids in cultured cortical astrocytes.
Population response of [Ca2+]i in cultured cortical astrocytes to excitatory amino acids was measured at room temperature using the calcium-sensitive dye fura-2. Quisqualic acid (QA), glutamate (Glu), and kainic acid (KA) caused a peak increase in [Ca2+]i in the order QA greater than Glu greater than KA. No response to N-methyl-D-aspartic acid (NMDA) was observed whether or not Mg2+ was present externally. Both QA and Glu (100 microM) frequently elicited a decaying oscillatory [Ca2+]i response during sustained agonist application; the period of oscillations initially was 23.5 sec and increased as the response was damped. Comparatively, the [Ca2+]i response to KA was nonoscillatory. Both responses to Glu and KA were reduced slightly by antagonist gamma-D-glutamylaminomethyl-sulfonic acid (1 mM), but virtually were abolished by kynurenic acid (3 mM). Replacement of external Na+ by choline had no significant effect on the Glu response. Removal of external Ca2+ reduced the peak response to QA, Glu, and KA to 40, 34, and 18%, respectively; and markedly reduced the degree of QA- and Glu-induced [Ca2+]i oscillations. Pretreatment with phorbol esters, a potent activator of protein kinase C, blocked the [Ca2+]i response to Glu but not KA. It is concluded that cortical astrocytes express Glu receptors of the non-NMDA type in culture and that receptor activation leads to Ca2+ influx and release of internal Ca2+. Mobilization of Ca2+ apparently occurs via the known Glu-mediated hydrolysis of inositol lipids, which may come under negative-feed-back control by protein kinase C activation. Oscillatory [Ca2+]i signaling offers the possibility of a dynamic population response in an electrically coupled glial network.
Jensen
A M
AM
Department of Neurophysiology, University of Wisconsin, Madison 53706.
Chiu
S Y
SY
D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D004594:Electrophysiology; D018691:Excitatory Amino Acid Antagonists; D005456:Fluorescent Dyes; D016257:Fura-2; D018698:Glutamic Acid; D007425:Intracellular Membranes / Q000378:metabolism* / Q000502:physiology; D008578:Meninges / Q000166:cytology / Q000378:metabolism; D009994:Osmolar Concentration; D011493:Protein Kinase C / Q000502:physiology; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D001572:Benzofurans; D018691:Excitatory Amino Acid Antagonists; D005456:Fluorescent Dyes; D018698:Glutamic Acid; D012964:Sodium; D011493:Protein Kinase C; D002118:Calcium; D016257:Fura-2