Basolateral dipeptide transport by the intestine of the teleost, oreochromis mossambicus.. Thamotharan, M., V. Zonno, C. Storelli, and G. A. Ahearn. Department of Physiology, University of Hawaii, Honolulu, Hawaii 96822, Laboratorio di Fisiologia, Universita di Lecce, Italy, Department of Zoology, University of Hawaii, Honolulu, Hawaii 96822
APStracts 2:0312R, 1995.
Transport characteristics of 14C-glycylsarcosine (14C-Gly-Sar) was measured in herbivorous tilapia (Oreochromis mossambicus) intestinal basolateral membrane vesicles (BLMV) purified with Percoll gradient centrifugation. Specific activity of the vesicle Na/K adenosinetriphosphatase was increased 12-fold, whereas specific activity of the brush border enzyme, alkaline phosphatase, was enriched only by 0.8-fold. 14C-Gly-Sar uptake was stimulated by increasing concentrations of extravesicular protons rather than by a transmembrane proton gradient. A transmembrane K+ diffusion potential (inside negative) did not stimulate 14C-Gly-Sar uptake above that observed with short-circuited vesicles. An inwardly-directed Na+ gradient had no effect on peptide uptake. Kinetic analysis of basolateral transport rate revealed that the transport occurred by a saturable process conforming to Michaelis-Menten kinetics (Kt = 13.27 +/- 3.80 mM, Jmax = 15155 +/- 3096 pmol/mg protein/6 sec). The basolateral transporter was insensitive to DEP (diethylpyrocarbonate), a specific inhibitor of proton-coupled peptide transport systems. 14C-Gly-Sar influx into tilapia BLMV showed cis inhibition by several other dipeptides, suggesting that the 14C-Gly-Sar transporter was shared by other peptides too. These observations strongly suggest that the basolateral intestinal dipeptide transporter in herbivorous fishes is distinctly different from either the high or low affinity brush border transporter. It is proton-dependent, electroneutral, sodium-independent, and accepts a wide variety of dipeptides. 

Received 16 May 1994; accepted in final form 26 September 1995.0
APS Manuscript Number R262-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95