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 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.
Hossain
Sheikh Julfikar
SJ
Department of Physics, Biology and Informatics, Faculty of Science, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8512, Japan.
Hamamoto
Koutaro
K
Aoshima
Hitoshi
H
Hara
Yukihiko
Y
D000080462:Acyclic Monoterpenes; D000818:Animals; D002392:Catechin / Q000031:analogs & derivatives / Q000494:pharmacology; D004357:Drug Synergism; D005260:Female; D015870:Gene Expression; D008564:Membrane Potentials / Q000187:drug effects; D039821:Monoterpenes; D009865:Oocytes / Q000378:metabolism*; D010936:Plant Extracts / Q000494:pharmacology*; D018075:RNA, Complementary / Q000235:genetics; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000502:physiology*; D011994:Recombinant Proteins; D013662:Tea / Q000737:chemistry*; D013729:Terpenes / Q000494:pharmacology; D014162:Transfection; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D000080462:Acyclic Monoterpenes; D039821:Monoterpenes; D010936:Plant Extracts; D018075:RNA, Complementary; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D013662:Tea; D013729:Terpenes; D005680:gamma-Aminobutyric Acid; D002392:Catechin; C062669:epicatechin gallate; C045651:epigallocatechin gallate; C018584:linalool; C007836:geraniol