Abstract
Adenylyl cyclase superactivation, a phenomenon by which chronic activation of inhibitory Gi/o-coupled receptors leads to an increase in cAMP accumulation, is believed to play an important role as a compensatory response of the cAMP signaling system in the cell. However, to date, the mechanism by which adenylyl cyclase activity is regulated by chronic exposure to inhibitory agonists and the nature of the adenylyl cyclase isozymes participating in this process remain largely unknown. Here we show, using COS-7 cells transfected with the various AC isozymes, that acute activation of the D2dopaminergic and m4 muscarinic receptors inhibited the activity of adenylyl cyclase isozymes I, V, VI, and VIII, whereas types II, IV, and VII were stimulated and type III was not affected. Conversely, chronic receptor activation led to superactivation of adenylyl cyclase types I, V, VI, and VIII and to a reduction in the activities of types II, IV, and VII. The activity of AC-III also was reduced. This pattern of inhibition/stimulation of the various adenylyl cyclase isozymes is similar to that we recently observed on acute and chronic activation of the μ-opioid receptor, suggesting that isozyme-specific adenylyl cyclase superactivation may represent a general means of cellular adaptation to the activation of inhibitory receptors and that the presence/absence and intensity of the adenylyl cyclase response in different brain areas (or cell types) could be explained by the expression of different adenylyl cyclase isozyme types in these areas.
Footnotes
- Received December 29, 1997.
- Accepted May 11, 1998.
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Send reprint requests to: Dr. Zvi Vogel, Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel. E-mail: bnvogel{at}weizmann.weizmann.ac.il
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This work was supported by the National Institute of Drug Abuse (Grant DA06265), German-Israeli Foundation for Scientific Research and Development, Forschheimer Center for Molecular Genetics, and Israeli Ministries of Science and Arts and of Absorption (fellowship to I.N.).
- The American Society for Pharmacology and Experimental Therapeutics
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