The expression and functional role of nicotinic acetylcholine receptors in rat adipocytes.
To clarify whether nicotine has a direct effect on the function of adipocytes, we evaluated nicotinic acetylcholine receptor (nAChR) expression in adipocytes by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry and the direct effects of nicotine on the production of adipocytokines by enzyme-linked immunosorbent assay and Western blot analysis. Receptor binding assays were performed using [3H]nicotine. RT-PCR studies revealed that alpha1-7, 9, 10, beta1-4, delta, and epsilon subunit mRNAs are expressed in adipocytes. Immunocytochemical experiments also suggested the presence of alpha7 and beta2 subunits. The receptor binding assay revealed a binding site for nicotine (Kd = 39.2 x 10(-9) M) on adipocytes. Adipocytes incubated with nicotine for 12 and 36 h released tumor necrosis factor-alpha (TNF-alpha), adiponectin, and free fatty acid (FFA) into the medium in a dose-dependent manner with increasing nicotine concentration from 6 x 10(-8) to 6 x 10(-4) M. However, TNF-alpha protein levels in adipocytes incubated for 12 and 36 h decreased in a dose-dependent manner with increasing nicotine concentration from 6 x 10(-8) to 6 x 10(-4) M. These results show that adipocytes have functional nAChRs and suggest that nicotine reduces TNF-alpha protein production in adipocytes through the activation of nAChRs. Nicotine may temporarily lower insulin sensitivity by stimulating the secretion of TNF-alpha and FFA, whereas long-term direct stimulation of nAChRs by nicotine in addition to autonomic nervous system stimulation may contribute to better insulin sensitivity in vivo through a modulated secretion of adipocytokines.
Third Department of Internal Medicine, Miyazaki Medical College, Miyazaki University, Kiyotake, Miyazaki, Japan.
Run-Hua
RH
Liu
Masanari
M
Mizuta
Shigeru
S
Matsukura
D017667:Adipocytes / Q000378:metabolism*; D052242:Adiponectin; D000818:Animals; D000906:Antibodies / Q000276:immunology; D002478:Cells, Cultured; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology*; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins; D008297:Male; D009538:Nicotine / Q000378:metabolism; D021122:Protein Subunits / Q000276:immunology; D011506:Proteins / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011978:Receptors, Nicotinic / Q000276:immunology / Q000378:metabolism* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014316:Tritium; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D064569:alpha7 Nicotinic Acetylcholine Receptor
D052242:Adiponectin; D000906:Antibodies; D005230:Fatty Acids, Nonesterified; D036341:Intercellular Signaling Peptides and Proteins; D009538:Nicotine; D021122:Protein Subunits; D011506:Proteins; D011978:Receptors, Nicotinic; D014316:Tritium; D014409:Tumor Necrosis Factor-alpha; D064569:alpha7 Nicotinic Acetylcholine Receptor; C579165:Chrna7 protein, rat