Abstract
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 α1–7, 9, 10, β1–4, δ, and ϵ subunit mRNAs are expressed in adipocytes. Immunocytochemical experiments also suggested the presence of α7 and β2 subunits. The receptor binding assay revealed a binding site for nicotine (Kd = 39.2 × 10-9 M) on adipocytes. Adipocytes incubated with nicotine for 12 and 36 h released tumor necrosis factor-α (TNF-α), adiponectin, and free fatty acid (FFA) into the medium in a dose-dependent manner with increasing nicotine concentration from 6 × 10-8 to 6 × 10-4 M. However, TNF-α protein levels in adipocytes incubated for 12 and 36 h decreased in a dose-dependent manner with increasing nicotine concentration from 6 × 10-8 to 6 × 10-4 M. These results show that adipocytes have functional nAChRs and suggest that nicotine reduces TNF-α protein production in adipocytes through the activation of nAChRs. Nicotine may temporarily lower insulin sensitivity by stimulating the secretion of TNF-α 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.
Footnotes
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ABBREVIATIONS: nAChRs, nicotinic acetylcholine receptors; TNF-α, tumor necrosis factor-α; FFA, free fatty-acid; RT-PCR, reverse transcriptase-polymerase chain reaction; PBS, phosphate-buffered saline; G3PDH, glyceraldehyde-3-phosphate dehydrogenase; bp, base pair(s).
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DOI: 10.1124/jpet.103.065037.
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↵1 Current address: Kishiwada City Hospital, 1001 Gakuhara, Kishiwada, Osaka 596-8501, Japan.
- Received December 29, 2003.
- Accepted March 1, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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