1. Nicotinic acetylcholine receptor [[alpha].sub.7] regulates cAMP signal within lipid rafts
- Author
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Oshikawa, Jin, Toya, Yoshiyuki, Fujita, Takayuki, Egawa, Masato, Kawabe, Junichi, Umemura, Satoshi, and Ishikawa, Yoshihiro
- Subjects
Acetylcholine -- Receptors ,Biological sciences - Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) are made of multiple subunits with diversified functions. The nAChR [[alpha].sub.7]-subunit has a property of high [Ca.sup.2+] permeability and may have specific functions and localization within the plasma membrane as a signal transduction molecule. In PC-12 cells, fractionation by sucrose gradient centrifugation revealed that nAChR[[alpha].sub.7] existed in low-density, cholesterol-enriched plasma membrane microdomains known as lipid rafts where flotillin also exists. In contrast, nAChR [[alpha].sub.5]- and [[beta].sub.2]-subunits were located in high-density fractions, out of the lipid rafts. Type 6 adenylyl cyclase (AC6), a calcium-inhibitable isoform, was also found in lipid rafts and was coimmunoprecipitated with nAChR[[alpha].sub.7] Cholesterol depletion from plasma membranes with methyl-[beta]-cyclodextrin redistributed nAChR[[alpha].sub.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 [alpha]-bungarotoxin, a specific antagonist of nAChR[[alpha].sub.7], or cholesterol depletion from plasma membranes. The effect of cholesterol depletion was negated by the addition of cholesterol. These data suggest that nAChR[[alpha].sub.7] has a specific membrane localization relative to other nAChR subunits and that lipid rafts are necessary to localize nAChR[[alpha].sub.7] with AC within plasma membranes. In addition, nAChR[[alpha].sub.7] may regulate the AC activity via [Ca.sup.2+] within lipid rafts. cholesterol; PC-12 cells
- Published
- 2003