Regulation of bradykinin-induced phosphoinositide turnover in cultured cerebellar astrocytes: possible role of protein kinase C.
Phosphoinositide hydrolysis was studied in primary cultures of rat cerebellar astrocytes prelabeled with [3H]myo-inositol. Among the agonists examined, the rank order of efficacies in causing phosphoinositide hydrolysis was bradykinin > endothelin-1 > ATP > norepinephrine. The bradykinin response was robust (24-fold increase) with EC50 value of 30 nM and saturating concentration of 1 microM. Preincubation of cells with pertussis toxin did not affect the activation of phosphoinositide turnover by bradykinin. Although short-term (within 90 min) treatment of cells with phorbol dibutyrate attenuated bradykinin-induced phosphoinositide breakdown, the inhibitory effect was lost after 3-6 h of phorbol dibutyrate treatment. Extended (24 h) preincubation resulted in a potentiation of bradykinin response. Homologous desensitization of bradykinin response was observed in cells prestimulated with bradykinin for up to 6 h. However, similar to the effect of phorbol dibutyrate, 24-h pretreatment with bradykinin selectively sensitized the response to bradykinin. Up-regulation of the bradykinin response was also observed in cells prestimulated with endothelin-1 or norepinephrine for 24 h, although these treatments resulted in only homologous desensitization to their own response. Our results suggest that cultured cerebellar astrocytes express bradykinin receptors coupled to phospholipase C and in these cells protein kinase C plays a more prominent role in the negative-feedback regulation of bradykinin-evoked phosphoinositide response.
Lin
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Section on Molecular Neurobiology, NIMH, Bethesda, MD 20892.
Chuang
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DM
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001920:Bradykinin / Q000494:pharmacology*; D002478:Cells, Cultured; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism*; D016232:Endothelins / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D037342:Pertussis Toxin; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D016232:Endothelins; D010716:Phosphatidylinositols; D010566:Virulence Factors, Bordetella; D015240:Phorbol 12,13-Dibutyrate; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D001920:Bradykinin; D009638:Norepinephrine