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7 regulates cAMP signal within lipid rafts
1 Departments of Physiology and Medicine, Yokohama City University School of Medicine, Yokohama, Kanagawa, Japan
2 Department of Medical Pathophysiology, Yokohama City University College of Nursing, Yokohama, Kanagawa, Japan
3 Cardiovascular Research Institute, Departments of Medicine and Cell Biology & Molecular Medicine, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, USA
4 Departments of Physiology and Medicine, Yokohama City University School of Medicine, Yokohama, Kanagawa, Japan; Cardiovascular Research Institute, Departments of Medicine and Cell Biology & Molecular Medicine, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, USA
* To whom correspondence should be addressed. E-mail: ishikayo{at}umdnj.edu.
Neuronal nicotinic acetylcholine receptors (nAChRs) are made of multiple subunits with diversified functions. nAChR
7 subunit has a property of high Ca2+ permeability, and may have specific functions and localization within the plasma membrane as a signal transduction molecule. In PC12 cells, fractionation by sucrose gradient centrifugation revealed that nAChR
7 existed in low density, cholesterol-enriched plasma membrane microdomains known as lipid rafts where flotillin also exists. In contrast, nAChR
5 and
2 subunits were located in high density fractions, out of lipid rafts. The type 6 adenylyl cyclase (AC6), a calcium-inhibitable isoform, was also found in lipid rafts, and was co-immunoprecipitated with nAChR
7. Cholesterol depletion from plasma membranes with methyl-
-cyclodextrin re-distributed nAChR
7 and AC6 diffusely within plasma membranes. Nicotine stimulation reduced forskolin-stimulated AC activity by 35%, and this inhibition was negated by either treatment with
-bungarotoxin, a specific antagonist of nAChR
7, or cholesterol depletion from plasma membranes. The effect of cholesterol depletion was negated by the addition of cholesterol. These data suggest that nAChR
7 has a specific membrane localization relative to other nAChR subunits, and that lipid rafts were necessary to localize nAChR
7 with AC within plasma membranes. In addition, nAChR
7 may regulate the AC activity via Ca2+ within lipid rafts.
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