Premium
Glutamate‐Stimulated, Guanine Nucleotide‐Mediated Phosphoinositide Turnover in Astrocytes Is Inhibited by Cyclic AMP
Author(s) -
Robertson Patricia L.,
Bruno George R.,
Datta Subhash C.
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.tb04962.x
Subject(s) - guanosine , forskolin , second messenger system , adenylate kinase , biology , cyclase , inositol , glutamate receptor , gtp' , protein kinase a , protein kinase c , biochemistry , intracellular , g protein , receptor , signal transduction , kinase , enzyme
The potential for cross‐talk between the adenyl cy‐clase and phosphoinositide (PPI) lipid second messenger system was investigated in astrocytes cultured from neonatal rat brain. Glutamate‐stimulated PPI turnover, measured by the formation of total inositol phosphates from myo ‐[ 3 H]inositoI‐labeled lipids, was inhibited in a concentration‐dependent manner by the elevation of intracellular cyclic AMP levels produced either by stimulation of the isoproter‐enol receptor linked to adenyl cyclase or by its direct activation by forskolin. N 6 ,2′‐ O ‐Dibutyryl cyclic AMP, an analogue that can also activate cyclic AMP‐dependent kinase, inhibited glutamate‐stimulated PPI turnover in a concentration‐dependent manner as well, a result suggesting that cyclic AMP‐dependent kinase is involved in mediating the inhibition. Inclusion of an inhibitor of cyclic AMP‐dependent kinase, l‐(5‐isoquinolinesulfonyl)‐2 methylpiperazine dihy‐drochloride or N ‐(2‐guanidinoethyl)‐5‐isoquinolinesulfon‐amide hydrochloride, blocked the cyclic AMP‐mediated inhibition in a concentration‐dependent manner, a finding further supporting this hypothesis. The site of inhibition of the phosphoinositol lipid pathway by cyclic AMP was probed using a digitonin‐permeabilized cell system. Guanosine 5′‐ O ‐(3‐thiotriphosphate), a nonhydrolyzable analogue of GTP, stimulated PPI turnover and potentiated glutamate‐stimulated PPI turnover, and guanosine 5′‐ O ‐(3‐thiodiphosphate) inhibited glutamate‐stimulated PPI turnover in these cells, results providing evidence that glutamate receptors are coupled to phospholipase C by a guanine nucleotide binding protein in astrocytes. N 6 ,2′‐ O ‐Dibutyryl cyclic AMP and agents that elevate cyclic AMP levels inhibited the PPI turnover stimulated by guanosine 5′‐ O ‐(3‐thiotriphosphate), as well as that potentiated by guanosine 5′‐ O ‐(3‐thiotriphos‐phate) in the presence of glutamate, results suggesting that the cyclic AMP‐dependent inhibition occurs at or distal to the putative guanine nucleotide binding protein. Because basal PPI turnover was not altered by elevation of cyclic AMP levels, direct inhibition of phospholipase C is unlikely.