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N ‐Acetylaspartylglutamate Inhibits Forskolin‐Stimulated Cyclic AMP Levels via a Metabotropic Glutamate Receptor in Cultured Cerebellar Granule Cells
Author(s) -
Wroblewska Barbara,
Wroblewski Jarda T.,
Saab Omar H.,
Neale Joseph H.
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.tb03606.x
Subject(s) - metabotropic receptor , biology , metabotropic glutamate receptor , forskolin , metabotropic glutamate receptor 6 , metabotropic glutamate receptor 1 , biochemistry , metabotropic glutamate receptor 5 , glutamate receptor , receptor , medicine
The neuronal dipeptide N ‐acetylaspartylglutamate (NAAG) fulfills several of the criteria for classification as a neurotransmitter including localization in synaptic vesicles, calcium‐dependent release after neuronal depolarization, and low potency activation of N ‐methyl‐ d ‐aspartate receptors. In the present study, the influence of NAAG on metabotropic receptor activation in cerebellar granule cells was examined in cell culture. Stimulation of granule cell adenylate cyclase with forskolin increased cyclic AMP (cAMP) several hundredfold above basal levels within 10 min in a concentration‐dependent manner. Although gluta‐mate, NAAG, and the metabotropic receptor agonist frans‐1‐amino‐1, 3‐cyclopentanedicarboxylic acid did not alter the low basal cAMP levels, the application of 300 μ M glutamate or NAAG or trans‐1‐amino‐1, 3‐cyclopentanedicarboxylic acid reduced forskolin‐stimulated cAMP in granule cells by 30–50% in the absence or presence of inhibitors of ionotropic acidic amino acid receptors, as well as 2‐amino‐4‐phosphonobutyrate. No additivity in the inhibition of cAMP was found when 300 μ M NAAG and trans ‐1‐amino‐1, 3‐cyclopentanedicarboxylic acid were coapplied. The β‐analogue of NAAG failed to reduce cAMP levels. Similar effects of NAAG and glutamate were obtained under conditions of inhibition of phosphodiesterase activity and were prevented by pretreatment of the cells with pertussis toxin. These data are consistent with the activation by NAAG of a metabotropic acidic amino acid receptor coupled to an inhibitory G protein. In contrast, the metabotropic acidic amino acid receptor coupled to phosphoinositol turnover in these cells was not activated by NAAG. Granule cells in culture expressed very low levels of extracellular peptidase activity against NAAG, converting to glutamate <0.1% of the 10 μ M through 1 m M NAAG applied to these cells during 15‐min in vitro assays.