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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

Background: Angiotensin II (AII) plays a central role in vascular remodeling via oxidative stress. However, the interaction between AII and reduced glutathione (GSH) redox status in cardiovascular remodeling remains unknown. Methods: In vivo: The cuff-induced vascular injury model was applied to Sprague Dawley rats. Then we administered saline or a GSH inhibitor, buthionine sulfoximine (BSO, 30 mmol/L in drinking water) for a week, subsequently administered 4 more weeks by osmotic pump with saline or AII (200 ng/kg/minute) to the rats. In vitro: Incorporation of bromodeoxyuridine (BrdU) was measured to determine DNA synthesis in cultured rat vascular smooth muscle cells (VSMCs). Results: BSO reduced whole blood GSH levels. Systolic blood pressure was increased up to 215±4 mmHg by AII at 4 weeks (p<0.01), which was not affected by BSO. Superoxide production in vascular wall was increased by AII and BSO alone, and was markedly enhanced by AII+BSO. The left ventricular weight to body weight ratio was significantly increased in AII and AII+BSO as compared to controls (2.52±0.08, 2.50±0.09 and 2.10±0.07 mg/g respectively, p<0.05). Surprisingly, the co-treatment of BSO totally abolished these morphological changes. Although the vascular circumferential wall stress was well compensated in AII, significantly increased in AII+BSO. The anti-single-stranded DNA staining revealed increasing apoptotic cells in the neointima of injured arteries in BSO groups. BrdU incorporation in cultured VSMCs with AII was increased dose-dependently. Furthermore it was totally abolished by BSO and was reversed by GSH monoethyl ester. Conclusions: We demonstrated that a vast oxidative stress in impaired GSH redox system totally abolished AII-induced vascular, not cardiac remodeling via enhancement of apoptosis in the neointima and suppression of cell growth in the media. The drastic suppression of remodeling may result in fragile vasculature intolerable to mechanical stress by AII. [ABSTRACT FROM AUTHOR]

Neuronal nicotinic acetylcholine receptors (nAChRs) are made of multiple subunits with diversified functions. The nAChR α[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 nAChRα[sub 7] existed in low-density, cholesterol-enriched plasma membrane microdomains known as lipid rafts where fiotillin also exists. In contrast, nAChR α[sub 5]- and β[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 nAChRα[sub 7]. Cholesterol depletion from plasma membranes with methylβ-cyclodextrin redistributed nAChRα[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 α-bungarotoxin, a specific antagonist of nAChRα[sub 7], or cholesterol depletion from plasma membranes. The effect of cholesterol depletion was negated by the addition of cholesterol. These data suggest that nAChRα[sub 7] has a specific membrane localization relative to other nAChR subunits and that lipid rafts are necessary to localize nAChRα[sub 7] with AC within plasma membranes. In addition, nAChRα[sub 7] may regulate the AC activity via Ca[sup 2+] within lipid rafts. [ABSTRACT FROM AUTHOR]

Objectives: Clinical impact of magnesium (Mg) therapy remains controversial in acute myocardial infarction. We investigated the infarct size limiting effects of Mg and its mechanism in rabbits. Methods: Anesthetized rabbits underwent 30 min coronary occlusion and 3 h reperfusion in ten groups: (1) Control, (2) Low Mg, (3) Mg, (4) High Mg, (5) calcium (Ca), (6) Mg+Ca, (7) 8-phenyltheophylline (8PT), an adenosine receptor blockade, (8) 8PT+Mg, (9) α, β-methylene-adenosine diphosphate (AOPCP), a selective inhibitor of ecto-5′-nucleotidase, and (10) AOPCP+Mg groups. Infract size (IS) to area at risk (AR) was measured by triphenyltetrazorium chloride method. Results: The IS/AR ratio was significantly smaller in Mg, 27±3% (P<0.05) and High Mg, 24±2% (P<0.05) compared to Control, 50±3% and Low Mg, 42±4%. The IS limiting effects of Mg were abolished in 8PT+Mg, AOPCP+Mg and Mg+Ca. The IS/AR ratio correlated with neither rate-pressure products nor incidence of arrhythmia. Conclusion: Magnesium administration has an infarct size limiting effect independent of its effects on myocardial oxygen consumption and incidence of arrhythmia in rabbits. The infarct size limiting effect of magnesium is attributable, at least in part, to augmentation of adenosine mechanism. [Copyright &y& Elsevier]