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Basolateral dipeptide transport by the intestine of the teleost Oreochromis mossambicus






American Journal of Physiology 270(5 Pt 2): R948-R954

Basolateral dipeptide transport by the intestine of the teleost Oreochromis mossambicus

Transport characteristics of (14C)glycylsarcosine ((14C)Gly-Sar) were 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 (K-t (concentration of (14C)Gly-Sar that yielded one-half of maximal influx (J-max)) = 13.27 +- 3.80 mM, J-max = 15,155 +- 3,096 pmol cntdot mg protein-1 cntdot 6 s-1). The basolateral transporter was insensitive to diethylpyrocarbonate (DEP), 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.


Accession: 002763128

PMID: 8928925



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