The stimulatory effect of the octadecaneuropeptide (ODN) on cytosolic Ca2+ in rat astrocytes is not mediated through classical benzodiazepine receptors.
Diazepam-binding inhibitor has been initially isolated from the rat brain from its ability to compete with benzodiazepines for their receptors. We have recently shown that the octadecaneuropeptide (diazepam-binding inhibitor-(33-50) or ODN) induces an increase in cytosolic free Ca2+ concentration ([Ca2+]i) in astroglial cells. The purpose of the present study was to determine whether central-type benzodiazepine receptors or peripheral-type benzodiazepine receptors are involved in the response of cultured rat astrocytes to ODN. The mixed central-/peripheral-type benzodiazepine receptor ligand flunitrazepam (10(-10) to 10(-6) M), the specific peripheral-type benzodiazepine receptor agonist Ro5-4864 (10(-10) to 10(-6) M) and the peripheral-type benzodiazepine receptor 'antagonist' PK 11195 (10(-9) to 10(-6) M) all induced a dose-dependent increase in [Ca2+]i. At high doses (10(-7) to 10(-5) M), the central-type benzodiazepine receptor agonist clonazepam also mimicked the stimulatory effect of ODN on [Ca2+]i. However, the [Ca2+]i rise induced by ODN was blocked neither by PK 11195 nor by the central-type benzodiazepine receptor antagonist flumazenil (10(-6) M each). Binding of [3H]flunitrazepam to intact astrocytes was displaced by low concentrations of the peripheral-type benzodiazepine receptor ligands flunitrazepam, Ro5 4864 and PK 11195, and by high concentrations of clonazepam. In contrast, ODN did not compete for [3H]flunitrazepam binding in intact cells. These data indicate that the effect of ODN on Ca2+ mobilization in rat astrocytes is mediated by high affinity receptors which are not related to classical benzodiazepine receptors.
Gandolfo
P
P
European Institute for Peptide Research (IFRMP No. 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U413, UA CNRS, University of Rouen, Mont-Saint-Aignan, France.
Patte
C
C
Leprince
J
J
Thoumas
J L
JL
Vaudry
H
H
Tonon
M C
MC
D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects* / Q000378:metabolism; D026261:Diazepam Binding Inhibitor; D005470:Fluorometry; D008024:Ligands; D009479:Neuropeptides / Q000494:pharmacology*; D010446:Peptide Fragments; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism / Q000502:physiology*
D026261:Diazepam Binding Inhibitor; D008024:Ligands; D009479:Neuropeptides; D010446:Peptide Fragments; D011963:Receptors, GABA-A; C067529:diazepam binding inhibitor (33-50)