Long-Term Effect of Forskolin on the Activation of Adenylyl Cyclase in Astrocytes |
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Authors: | Amina El Jamali,Nadia Rachdaoui,Claude Jacquemin, Claude Corrè ze |
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Affiliation: | Unitéde Recherche sur la Glande Thyroïde et la Régulation Hormonale, U. 96 INSERM, Institut Fédératif de Recherche "Hormones et Génétique," Le Kremlin-Bicêtre, France |
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Abstract: | Abstract: Long-term (48-h) forskolin treatment of rat astroglial cells led to a slight decrease (30–40%) in the response to isoproterenol, vasoactive-intestinal peptide, guanyl 5'-(βγ-imido)diphosphate, guanosine 5'- O -(3-thiotriphosphate) [GTP(S)], and AIF4− in crude membrane fractions. In contrast, the acute stimulatory effect of forskolin was increased by 1.25–1.5-fold. These two opposite effects of forskolin were mediated by a cyclic AMP-dependent mechanism. No changes in Gsα, Giα, or Gβ protein levels could be determined by immunoblotting using specific antisera. No significant differences were observed in the ability of G proteins extracted from control and forskolin-treated cells to reconstitute a full adenylyl cyclase activity in membranes from S49 cyc− cells, lacking Gsα protein. Gsα proteins were detected in two pools of membranes, one in the heavy sucrose fractions and the other in light sucrose fractions. Forskolin treatment of the cells shifted Gsα protein toward the light-density membranes. We did not find any significant change in the distribution of adenylyl cyclase. In contrast to the decreased stimulation of adenylyl cyclase activity by agonists acting via Gsα, observed in the crude membrane fraction, the responses of adenylyl cyclase to forskolin as well as to GTP(S) were increased in the purified plasma membrane fractions. These results may indicate that sensitization of the catalyst appears to be the dominant component in the astroglial cell response to long-term treatment by forskolin. |
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Keywords: | ATP pyrophosphate-lyase (cyclizing) (EC 4.6.1.1) Desensitization Up-regulation G protein Western blotting Subcellular fractionation Astroglial cells |
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