Effects of tea components on the response of GABA(A) receptors expressed in Xenopus Oocytes

To study the effects of tea components on ionotropic gamma-aminobutyric acid (GABA) receptor response, ionotropic GABA receptors (GABA(A) receptors) were expressed in Xenopus oocytes by injecting cRNAs synthesized from cloned cDNAs of the alpha(1) and beta(1) subunits of the bovine receptors, and th...

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Published in:Journal of agricultural and food chemistry 2002-07, Vol.50 (14), p.3954-3960
Main Authors: Hossain, Sheikh Julfikar, Hamamoto, Koutaro, Aoshima, Hitoshi, Hara, Yukihiko
Format: Article
Language:English
Subjects:
Animals
Catechin - analogs & derivatives
Catechin - pharmacology
Drug Synergism
Female
gamma-Aminobutyric Acid - pharmacology
Gene Expression
Membrane Potentials - drug effects
Monoterpenes
Oocytes - metabolism
Plant Extracts - pharmacology
Receptors, GABA-A - drug effects
Receptors, GABA-A - physiology
Recombinant Proteins
RNA, Complementary - genetics
Tea - chemistry
Terpenes - pharmacology
Transfection
Xenopus laevis
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Summary:To study the effects of tea components on ionotropic gamma-aminobutyric acid (GABA) receptor response, ionotropic GABA receptors (GABA(A) receptors) were expressed in Xenopus oocytes by injecting cRNAs synthesized from cloned cDNAs of the alpha(1) and beta(1) subunits of the bovine receptors, and their electrical responses were measured by a voltage clamping method. Extracts of green tea, black tea, and oolong tea in an aqueous solution induced the GABA-elicited response, which showed that these teas contain GABA, whereas coffee does not. Caffeine weakly inhibited the response in a competitive manner (K(i) = 15 mM), and (+)-catechin inhibited it in a noncompetitive one (K(i) = 1.7 mM). Especially, two catechin derivatives, (-)-epicatechin gallate and (-)-epigallocatechin gallate, inhibited the response strongly. Alcohols such as leaf alcohol or linalool potentiated the response, possibly because their binding to the potentiation site enhances the GABA-binding affinity to GABA(A) receptors when they bind. Extracts of green tea made with ethyl ether, which must contain lipophilic components of green tea, inhibited the response elicited by GABA, possibly because the amounts of caffeine and catechin derivatives were much larger than fragrant alcohols in such extracts of tea.
ISSN:0021-8561
1520-5118
DOI:10.1021/jf011607h