The rat intestinal imino acid carrier is chloride independent, while in guinea pig and rabbit intestine it is chloride dependent. While non-α-amino acids do not significantly interact with guinea pig and rabbit imino acid carriers, inhibition studies had indicated that in rat small intestine β- alanine, γ-aminobutyric acid (GABA), and probably taurine might be transported by the imino acid carrier. The present study of rat jejunum demonstrates that the half-maximal activation concentration of β-alanine (K( 1/2 )/(β-Ala)) is identical to its inhibition constant (K(i)/(β-Ala)) against GABA, that K( 1/2 )/(GABA) is identical to K(i)/(GABA) against β- alanine, that proline and sarcosine have identical values of K(i) against β- alanine and GABA, and that K(i) of β-alanine and proline against sarcosine are equal to their K( 1/2 ) values. Taurine inhibits the transport of β- alanine, and 300 mM proline and β-alanine reduce the transport of taurine measured at 80 mM taurine to the level expected for the diffusive contribution, corresponding to K(i) values equal to those against sarcosine. Thus the rat imino acid carrier is the principal carrier of taurine and the only carrier of β-alanine and GABA. It is also demonstrated that α-amino- monocarboxylic acids with side chains in excess of one methyl group do not significantly interact with the imino acid carrier, and the lack of stereospecificity is confirmed.
|Tidsskrift||American Journal of Physiology - Regulatory Integrative and Comparative Physiology|
|Udgave nummer||4 35-4|
|Status||Udgivet - 1 jan. 1994|