Quercetin Enhances Human ${\alpha}$7 Nicotinic Acetylcholine Receptor-Mediated Ion Current through Interactions with $Ca^{2+}$ Binding Sites

• Published in: Molecules and cells 2010, Vol.30 (3), p.245-253
• Main Authors: Lee, Byung-Hwan, Choi, Sun-Hye, Shin, Tae-Joon, Pyo, Mi-Kyung, Hwang, Sung-Hee, Kim, Bo-Ra, Lee, Sang-Mok, Lee, Jun-Ho, Kim, Hyoung-Chun, Park, Hye-Young, Rhim, Hye-Whon, Nah, Seung-Yeol
• Format: Article
• Language: Korean
• ISSN: 1016-8478; 0219-1032

The flavonoid quercetin is a low molecular weight substance found in fruits and vegetables. Aside from its antioxidative effect, quercetin, like other flavonoids, has a wide range of neuropharmacological actions. The ${\alpha}$7 nicotinic acetylcholine receptor (${\alpha}$7 nAChR) has a $Ca^{2+}$-binding site, is highly permeable to the $Ca^{2+}$ ion, and plays important roles in $Ca^{2+}$-related normal brain functions. Dysfunctions of ${\alpha}$7 nAChR are associated with a variety of neurological disorders. In the present study, we investigated the effects of quercetin on the ACh-induced inward peak current ($I_{ACh}$) in Xenopus oocytes that heterologously express human ${\alpha}$7 nAChR. $I_{ACh}$ was measured with the two-electrode voltage clamp technique. In oocytes injected with ${\alpha}$7 nAChR cRNA, the effects of the co-application of quercetin on $I_{ACh}$ were concentration-dependent and reversible. The $ED_{50}$ was 36.1 + 6.1 ${\mu}m$. Quercetin-mediated enhancement of $I_{ACh}$ caused more potentiation when quercetin was preapplied. The degree of $I_{ACh}$ potentiation by quercetin preapplication was time-dependent and saturated after 1 min. Quercetin-mediated $I_{ACh}$ enhancement was not affected by ACh concentration and was voltage-independent. However, quercetin-mediated $I_{ACh}$ enhancement was dependent on extracellular $Ca^{2+}$ concentrations and was specific to the $Ca^{2+}$ ion, since the removal of extracellular $Ca^{2+}$ or the addition of $Ba^{2+}$ instead of $Ca^{2+}$ greatly diminished quercetin enhancement of $I_{ACh}$. The mutation of Glu195 to Gln195, in the $Ca^{2+}$-binding site, almost completely diminished quercetin-mediated $I_{ACh}$ enhancement. These results indicate that quercetin-mediated $I_{ACh}$ enhancement human ${\alpha}$7 nAChR heterologously expressed in Xenopus oocytes could be achieved through interactions with the $Ca^{2+}$-binding site of the receptor.