TRANSMURAL POTENTIAL CHANGES ASSOCIATED WITH THE IN-VITRO ABSORPTION OF THEANINE IN THE GUINEA-PIG INTESTINE

Theanine, L-N-ethylglutamine, is one of the major components of amino acids in Japanese green tea. To characterize the mode for intestinal a bsorption of theanine, the ionic dependency and kinetic properties of the theanine- and glutamine-evoked transmural electrical potential dif ference changes (Delta PD) were investigated in vitro by using everted sacs prepared from the guinea pig ileum. Both theanine and glutamine applied to the luminal side induced dose-dependent increases in Delta PD (increase in serosal positive value). The theanine- and glutamine-e voked Delta PD values conformed to the Michaelis-Menten relationship, with Delta PDmax not being different, whereas the half-saturation conc entration was lower for glutamine (3.1 +/- 0.2 mM) than for theanine ( 21.4 +/- 0.6 mM). The theanine-evoked Delta PD value was much smaller when theanine was applied in the presence of glutamine than when appli ed alone. The theanine- and glutamine-evoked Delta PD values were both inhibited by removing Na+ from the luminal solution. These results su ggest that the intestinal absorption of theanine and glutamine is medi ated by a common Na+-coupled co-transporter in the brush-border membra ne, the affinity of which is lower for theanine than for glutamine.