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Presynaptic Glutamate/Quisqualate Receptors: Effects on Synaptosomal Free Calcium Concentrations
Author(s) -
Adamson P.,
Hajimohammadreza I.,
Brammer M. J.,
Campbell I. C.,
Meldrum B. S.
Publication year - 1990
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.1471-4159.1990.tb05767.x
Subject(s) - cnqx , ampa receptor , glutamate receptor , metabotropic glutamate receptor , endocrinology , nmda receptor , medicine , metabotropic receptor , chemistry , metabotropic glutamate receptor 1 , biology , biochemistry , receptor
Intracellular free [Ca 2+ ] j was measured using fura‐2 in synaptosomes prepared from cerebral cortices of adult male rats (12 weeks). L‐(+)‐Glutamate, d‐(‐)‐glutamate, and quisqualate produced similar dose‐dependent increases in [Ca 2+ ] i , with EC 50 values of 0.38 μ M , 0.74 μ M , and 0.1 μ M , respectively, and maximum increases of approximately 40%. Ibotenate showed less affinity (EC 50 4.4 μ M ) but had a greater maximum effect (57%). N ‐methyl‐d‐aspartate (NMDA) and α‐ amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) did not increase [Ca 2+ ] i‐ The increases in [Ca 2+ ] i induced by quisqualate and ibotenate were not diminished in the absence of extrasynaptosomal Ca 2+ . l‐2‐Amino‐4‐phosphonobutyrate (L‐AP4) (1 μ M ) completely blocked the changes in [Ca 2+ ] i induced by l‐(+)‐glutamate, d‐(‐)‐glutamate, quisqualate, or ibotenate. The effects of quisqualate and ibotenate on [Ca 2+ ] i were also blocked by coincubation of synaptosomes with l‐(+)‐serine‐ O ‐phosphate (L‐SP) (1 m M ) (which, like L‐AP4, blocks the effects of quisqualate and ibotenate on inositol phospholipid metabolism). 6‐Cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) had no effect on agonist‐mediated increases in [Ca 2+ ] i when coincubated with either quisqualate or ibotenate. These data are consistent with the existence of presynaptic glutamate receptors (of the excitatory amino acid metabotropic type) which activate phospholipase C leading to the elevation of inositol 1,4,5‐trisphosphate and release of Ca 2+ from intracellular stores.