AJP - Gastrointestinal and Liver Physiology, Vol 247, Issue 1 43-G51, Copyright © 1984 by American Physiological Society
Mechanisms of transport of L-histidine and beta-alanine in hamster small intestine
F. Navab, S. S. Beland, D. J. Cannon and E. C. Texter Jr
Whole rings of hamster jejunum and ileum were used to study the uptake of
L-histidine (L-His) and beta-alanine (beta-Ala), the constituents of the
dipeptide carnosine. The rate of uptake of L-His and beta-Ala (1 mM) was
not significantly different in the jejunum compared with the ileum. Results
of total influx (2 min) of 0.5-100 mM L-His suggested that transport was by
more than one pathway, and the contribution of nonmediated component was
calculated to be 0.24 mumol X g-1 X 2 min-1 X mM-1 for both jejunum and
ileum. The apparent affinity of L-His for a transporter was higher in the
ileum (K iota, 8.0 mM) than the jejunum (Kt, 11.7 mM). Influx (2 min) of
beta-Ala was found to be linearly related to substrate concentration over
the range 0.5-100 mM. The Kd (rate constant for nonmediated uptake of
beta-Ala) was 0.23 and 0.14 mumol X g-1 X 2 min-1 X mM-1 for jejunum and
ileum, respectively. Steady-state (20-min) uptake of L-His was
significantly higher in the ileum than jejunum at substrate concentrations
of 75 mM. L-His accumulated in the tissue up to a medium concentration of
50 mM in the jejunum and 75 mM in the ileum. In contrast, no evidence of
tissue accumulation of beta-Ala was found in 20-min incubations. beta-Ala
steady-state uptake in the ileum was significantly higher than in the
jejunum at substrate concentrations of 30 and 75 mM.
