The endogenous benzodiazepine receptor ligand ODN increases cytosolic calcium in cultured rat astrocytes.
We have investigated the production of diazepam-binding inhibitor (DBI)-related peptides by astrocytes in primary culture and we have determined the effect of the octadecaneuropeptide DBI[33-50] (ODN) on the intracellular calcium concentration ([Ca2+]i) in astrocytes. Immunocytochemical labeling with antibodies against ODN showed that cultured astrocytes retain their ability to synthesize DBI in vitro. Cultured astrocytes were also found to release substantial amounts of ODN-immunoreactive material, and a brief exposure of astrocytes to a depolarizing potassium concentration resulted in a 5-fold increase in the rate of release of the ODN-like peptide. Microfluorimetric measurement of [Ca2+]i with the fluorescent probe indo-1 showed that nanomolar concentrations of ODN induced a marked increase in [Ca2+]i. The stimulatory effect of ODN on [Ca2+]i was not affected by calcium channel blockers or by incubation in Ca(2+)-free medium. In contrast, thapsigargin, an inhibitor of microsomal Ca(2+)-ATPase activity, totally abolished the ODN-induced increase in [Ca2+]i. Repeated pulses of ODN caused attenuation of the response, indicating the existence of a desensitization phenomenon. Preincubation of astrocytes with pertussis toxin totally blocked the effect of ODN on [Ca2+]i. The present study indicates that ODN-related peptides are synthesized and released by glial cells. Our results also show that synthetic ODN induces calcium mobilization from an intracellular store through stimulation of pertussis toxin-sensitive G protein. Taken together, these data suggest that endozepines act as paracrine and/or autocrine factors controlling the activity of astroglial cells.
Lamacz
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European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U413, UA CNRS, University of Rouen, Mont-Saint-Aignan, France.
Tonon
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MC
Smih-Rouet
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Patte
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Gasque
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Fontaine
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Vaudry
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D000818:Animals; D001253:Astrocytes / Q000187:drug effects*; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D026261:Diazepam Binding Inhibitor; D004305:Dose-Response Relationship, Drug; D007150:Immunohistochemistry; D009479:Neuropeptides / Q000494:pharmacology*; D010446:Peptide Fragments; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000187:drug effects*
D026261:Diazepam Binding Inhibitor; D009479:Neuropeptides; D010446:Peptide Fragments; D011963:Receptors, GABA-A; C067529:diazepam binding inhibitor (33-50); D002104:Cadmium; D002118:Calcium