Fluorescence method shows how nicotine receptors are grouped on brain cells

Nicotine, the primary compound found within tobacco smoke, is known to change the grouping of some subtypes of nicotinic receptors, but the mechanisms for nicotine addiction remain unclear. Recognizing this, a team of researchers at the University of Kentucky (Lexington, KY) has developed a fluorescence single-molecule technique to explore the role that nicotine plays in the assembly of nicotinic receptors within the brain.

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Faruk Moonschi, a graduate student in the Department of Chemistry at the University of Kentucky, has long been interested in what leads to nicotine dependency. So, he and the other researchers explored whether nicotine exposure increases the total number of nicotinic receptors on cell surfaces and if it changes the way the receptor is grouped. "To do this, we use custom-built microscopes to expose our samples to laser excitation while we detect the fluorescence signal given off from the labeled proteins," Moonschi explains.

Generally, a ligand—which can be a small molecule or peptide—binds with the corresponding receptor protein on its cell surface and causes an effect. "Contrary to this general process, some researchers hypothesized that nicotine actually gets inside the cells of smokers' brains and changes the assembly of nicotinic receptors by altering the ratio of nicotinic receptor subunits and potentially altering the trafficking of some subtypes of nicotinic receptors to the cell surface," Moonschi says.

So, Moonschi and colleagues developed a single-molecule technique that allows them to separate freshly assembled nicotinic receptors from the endoplasmic reticulum of cells from those already assembled and transferred to the cell surface. "By doing this, we were able to show that nicotine changes the subunit ratio of nicotinic receptors in the endoplasmic reticulum," Moonschi says. "Further, we showed that one assembly is preferentially transported from the endoplasmic reticulum to the plasma membrane."

These findings are an important contribution to understanding the mechanism of nicotine addiction. "Understanding how nicotine alters the assembly of receptors in the context of addiction should provide insight into therapeutic targets for smoking cessation compounds," Moonschi notes.

Next, the research team plans to expand to in vivo studies using genetically modified mice to determine whether similar changes in stoichiometry are seen in live animals because of nicotine exposure, Moonschi explains. They also plan to study how smoking cessation compounds affect the stoichiometry of nicotinic receptors.

Moonschi presented the research team's work during the Biophysical Society's 61st Annual Meeting on February 13, 2017, in New Orleans, LA. To view the abstract, please visit http://www.abstractsonline.com/pp8/#!/4279/presentation/3107.