Influx of D-aspartate (D-Asp), L-glutamate (L-Glu), and serine (Ser) across the brush-border membrane of the intact mucosa from rabbit ileum has been examined. L-Glu influx is chloride independent and completely sodium dependent. D-Asp and L-Glu share a transport system with a maximum transport rate of 1 µmol · cm² · h¹ and an apparent affinity constant (K_1/2) of ~0.3 mM. The function of this transport system is pH insensitive between pH 5.65 and 8.2, and bipolar amino acids do not affect the way in which the transport system handles D-Asp and L-Glu. The characteristics of this transport system match those of system X_AG. L-Glu and Ser share a transporter for which the inhibitor constant (K_i) of L-Glu against Ser decreases from 54 to 10 mM when pH is reduced from 7.2 to 5.65, while the maximum rate of transport remains unaffected at ~10 µmol · cm² · h¹. The K_i values (5 mM) of Ser against L-Glu influx and the L-Glu-sensitive contribution to Ser influx (0.8 µmol · cm² · h¹ at 1 mM Ser) are the same at both pH values. The L-Glu-sensitive transport of Ser together with the contribution of system b^o,+ account for ~50% of Ser influx at pH 7.2. The remaining 50% can be ascribed to system B. Transport of Ser by system B is reduced by >95% at pH 5.65. At pH 7.2 K_i of Ser against transport of leucine (Leu) by system B is 18 mM and K_i of Leu against transport of Ser is 1.7 mM. The low-affinity transport of L-Glu and the L-Glu-sensitive transport of Ser are performed by an equivalent of system ASC. Supplementary experiments using the jejunum confirm the validity of these results for a major portion of the rabbit small intestine.

anionic amino acids; biological transport; amino acids; brush-border membrane; intestine

This article has been cited by other articles:

				J. R. Talukder, R. Kekuda, P. Saha, S. Arthur, and U. Sundaram Identification and characterization of rabbit small intestinal villus cell brush border membrane Na-glutamine cotransporter Am J Physiol Gastrointest Liver Physiol, July 1, 2008; 295(1): G7 - G15. [Abstract] [Full Text] [PDF]

				S. Broer Apical Transporters for Neutral Amino Acids: Physiology and Pathophysiology Physiology, April 1, 2008; 23(2): 95 - 103. [Abstract] [Full Text] [PDF]

				S. Broer Amino Acid Transport Across Mammalian Intestinal and Renal Epithelia Physiol Rev, January 1, 2008; 88(1): 249 - 286. [Abstract] [Full Text] [PDF]

				A. Blikslager, E. Hunt, R. Guerrant, M. Rhoads, and R. Argenzio Glutamine transporter in crypts compensates for loss of villus absorption in bovine cryptosporidiosis Am J Physiol Gastrointest Liver Physiol, September 1, 2001; 281(3): G645 - G653. [Abstract] [Full Text] [PDF]

				M. Wasa, H.-S. Wang, and A. Okada Characterization of L-glutamine transport by a human neuroblastoma cell line Am J Physiol Cell Physiol, June 1, 2002; 282(6): C1246 - C1253. [Abstract] [Full Text] [PDF]