THE ENDOGENOUS BENZODIAZEPINE RECEPTOR-LIGAND ODN INCREASES CYTOSOLICCALCIUM IN CULTURED RAT ASTROCYTES

We have investigated the production of diazepam-binding inhibitor (DBI )-related peptides by astrocytes in primary culture and we have determ ined the effect of the octadecaneuropeptide DBI[33-50] (ODN) on the in tracellular calcium concentration ([Ca2+](i)) in astrocytes. Immunocyt ochemical labeling with antibodies against ODN showed that cultured as trocytes retain their ability to synthesize DBI in vitro. Cultured ast rocytes were also found to release substantial amounts of ODN-immunore active material, and a brief exposure of astrocytes to a depolarizing potassium concentration resulted in a 5-fold increase in the rate of r elease of the ODN-like peptide. Microfluorimetric measurement of [Ca2](i) with the fluorescent probe indo-1 showed that nanomolar concentra tions of ODN induced a marked increase in [Ca2+](i). The stimulatory e ffect of ODN on [Ca2+](i) was not affected by calcium channel blockers or by incubation in Ca2+-free medium. in contrast, thapsigargin, an i nhibitor of microsomal Ca2+-ATPase activity, totally abolished the ODN -induced increase in [Ca2+](i). Repeated pulses of ODN caused attenuat ion of the response, indicating the existence of a desensitization phe nomenon. Preincubation of astrocytes with pertussis toxin totally bloc ked the effect of ODN on [Ca2+](i). The present study indicates that O DN-related peptides are synthesized and released by glial cells. Our r esults also show that synthetic ODN induces calcium mobilization from an intracellular store through stimulation of pertussis toxin-sensitiv e G protein. Taken together, these data suggest that endozepines act a s paracrine and/or autocrine factors controlling the activity of astro glial cells.