Naringin directly activates inwardly rectifying potassium channels at an overlapping binding site to tertiapin-Q

作者：Yow Tin T; Pera Elena; Absalom Nathan; Heblinski Marika; Johnston Graham A R; Hanrahan Jane R; Chebib Mary^*

来源：British Journal of Pharmacology, 2011, 163(5): 1017-1033.

DOI：10.1111/j.1476-5381.2011.01315.x

• flavonoids
• flavonoid glycosides
• G protein-coupled inwardly rectifying potassium channels
• G protein-coupled receptor
• naringin
• tertiapin-Q

BACKGROUND
G protein-coupled inwardly rectifying potassium (K(IR)3) channels are important proteins that regulate numerous physiological processes including excitatory responses in the CNS and the control of heart rate. Flavonoids have been shown to have significant health benefits and are a diverse source of compounds for identifying agents with novel mechanisms of action.
EXPERIMENTAL APPROACH
The flavonoid glycoside, naringin, was evaluated on recombinant human K(IR)3.1-3.4 and K(IR)3.1-3.2 expressed in Xenopus oocytes using two-electrode voltage clamp methods. In addition, we evaluated the activity of naringin alone and in the presence of the K(IR)3 channel blocker tertiapin-Q (0.5 nM, 1 nM and 3 nM) at recombinant K(IR)3.1-3.4 channels. Site-directed mutagenesis was used to identify amino acids within the M1-M2 loop of the K(IR)3.1F137S mutant channel important for naringin's activity.
KEY RESULTS
Naringin (100 mu M) had minimal effect on uninjected oocytes but activated K(IR)3.1-3.4 and K(IR)3.1-3.2 channels. The activation by naringin of K(IR)3.1-3.4 channels was inhibited by tertiapin-Q in a competitive manner. An alanine-scan performed on the K(IR)3.1F137S mutant channel, replacing one by one aromatic amino acids within the M1-M2 loop, identified tyrosines 148 and 150 to be significantly contributing to the affinity of naringin as these mutations reduced the activity of naringin by 20- and 40-fold respectively.
CONCLUSIONS AND IMPLICATIONS
These results show that naringin is a direct activator of K(IR)3 channels and that tertiapin-Q shares an overlapping binding site on the K(IR)3.1-3.4. This is the first example of a ligand that activates K(IR)3 channels by binding to the extracellular M1-M2 linker of the channel.

• 出版日期2011-7