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Quercetin Enhances Human α7 Nicotinic Acetylcholine Receptor-Mediated Ion Current through Interactions with Ca 2+ Binding Sites

Molecules and Cells, ISSN: 1016-8478, Vol: 30, Issue: 3, Page: 245-254
2010
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The flavonoid quercetin is a low molecular weight substance found in fruits and vegetables. Aside from its anti-oxidative effect, quercetin, like other flavonoids, has a wide range of neuropharmacological actions. The α7 nicotinic acetylcholine receptor (α7 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 α7 nAChR are associated with a variety of neuro-logical disorders. In the present study, we investigated the effects of quercetin on the ACh-induced inward peak current ( IACh ) in Xenopus oocytes that heterologously express human α7 nAChR. IACh was measured with the two-electrode voltage clamp technique. In oocytes injected with α7 nAChR cRNA, the effects of the co-application of quercetin on IACh were concentration-dependent and reversible. The ED 50 was 36.1 + 6.1 μM. Quercetin-mediated enhancement of IACh caused more potentiation when quercetin was pre-applied. The degree of IACh potentiation by quercetin pre-application was time-dependent and saturated after 1 min. Quercetin-mediated IACh enhancement was not affected by ACh concentration and was voltage-independent. However, quercetin-mediated IACh 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 IACh. The mutation of Glu195 to Gln195, in the Ca 2+ -binding site, almost completely diminished quercetin mediated IACh enhancement. These results indicate that quercetin-mediated IACh enhancement human α7 nAChR heterologously expressed in Xenopus oocytes could be achieved through interactions with the Ca 2+ -binding site of the receptor.

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