Polyphenol-induced inhibition of the response of na(+)/glucose cotransporter expressed in Xenopus oocytes.
To study the effects of polyphenols on the Na(+)/glucose cotransporter (SGLT1) response, SGLT1 was expressed in Xenopus oocytes by injecting cRNA synthesized from the cloned cDNA of the small intestine cotransporter of rats, and the electrical response elicited by glucose or galactose was measured by a voltage clamping method. Most phenol derivatives had no effect on the response. However, the polyphenols (+)-catechin, (-)-epicatechin gallate (ECg), and (-)-epigallocatechin gallate (EGCg), which are components of green tea, caused an inhibition of the response, which was almost independent of glucose concentration. The inhibition constants were estimated to be 2.3 mM for (+)-catechin and 0.45 mM for both ECg and EGCg, assuming the noncompetitive inhibition mechanism. Saponin prepared from tea seeds also inhibited the response significantly. Tannic acid and aqueous extracts of teas induced nonspecific electrical responses in both cRNA-injected and noninjected oocytes at lower concentrations than those that caused an inhibition of the SGLT1 response when their dose-dependent effects were examined. These results are possibly helpful in the development of a dietary supplement for diabetic patients.
Department of Physics, Biology and Informatics, Faculty of Science, Yamaguchi University, 1677-1 Yoshida, Japan.
Sheikh Julfikar
SJ
Hossain
Hiroko
H
Kato
Hitoshi
H
Aoshima
Terufumi
T
Yokoyama
Mamoru
M
Yamada
Yukihiko
Y
Hara
D000818:Animals; D002392:Catechin / Q000031:analogs & derivatives / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D005260:Female; D005419:Flavonoids; D005690:Galactose / Q000494:pharmacology; D015870:Gene Expression; D005947:Glucose / Q000494:pharmacology; D007421:Intestine, Small / Q000737:chemistry; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D010636:Phenols / Q000494:pharmacology*; D011108:Polymers / Q000494:pharmacology*; D051381:Rats; D012503:Saponins / Q000494:pharmacology; D051269:Sodium-Glucose Transporter 1; D013662:Tea / Q000737:chemistry; D014982:Xenopus laevis
D005419:Flavonoids; D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D010636:Phenols; D011108:Polymers; D012503:Saponins; C495676:Slc5a1 protein, rat; D051269:Sodium-Glucose Transporter 1; D013662:Tea; D002392:Catechin; C062669:epicatechin gallate; C045651:epigallocatechin gallate; D005947:Glucose; D005690:Galactose