Glutamate-stimulated, guanine nucleotide-mediated phosphoinositide turnover in astrocytes is inhibited by cyclic AMP.
The potential for cross-talk between the adenyl cyclase 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-[3H]inositol-labeled lipids, was inhibited in a concentration-dependent manner by the elevation of intracellular cyclic AMP levels produced either by stimulation of the isoproterenol receptor linked to adenyl cyclase or by its direct activation by forskolin. N6,2'-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, 1-(5-isoquinolinesulfonyl)-2 methylpiperazine dihydrochloride or N-(2-guanidinoethyl)-5-isoquinolinesulfonamide 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.(ABSTRACT TRUNCATED AT 250 WORDS)
Robertson
P L
PL
Department of Pediatrics, University of Michigan, Ann Arbor.
Bruno
G R
GR
Datta
S C
SC
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D004072:Digitonin / Q000494:pharmacology; D004338:Drug Combinations; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D006150:Guanine Nucleotides / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013873:Thionucleotides / Q000494:pharmacology
D004338:Drug Combinations; D005971:Glutamates; D006150:Guanine Nucleotides; D010716:Phosphatidylinositols; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D018698:Glutamic Acid; D003994:Bucladesine; C023427:guanosine 5'-O-(2-thiodiphosphate); D000242:Cyclic AMP; D004072:Digitonin; D007545:Isoproterenol; D002118:Calcium