AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 3 506-R510, Copyright © 1989 by American Physiological Society
Brush-border amino acid transport mechanisms in carnivorous eel intestine
C. Storelli, S. Vilella, M. P. Romano, M. Maffia and G. Cassano
Dipartimento di Biologia, Universita di Lecce, Italy.
Brush-border membrane vesicles (BBMV) were prepared from European eel
(Anguilla anguilla) intestinal epithelium by a magnesium-ethylene
glycolbis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)
precipitation technique. Amino acid transport by these purified vesicle
preparations was investigated using either radiolabeled substrates or the
voltage-sensitive fluorescent dye 3,3'-diethylthiadicarbocyanine iodide
[DiSC2(5)]. All amino acids tested exhibited carrier-mediated,
Na+-dependent and Na+-independent transfer processes plus diffusion. The
only exceptions were glutamic acid and proline, which displayed Na+
dependency and diffusion but did not appear to be transported by
Na+-independent agencies. Carrier-mediated transport kinetic constants
(Kapp and Jmax) for several amino acids are reported. Cis-inhibition
experiments suggested the presence of at least four distinct Na+-dependent
transport systems in eel intestinal BBMV: 1) an anionic transport process
for glutamic and aspartic acids; 2) a cationic mechanism for lysine and
arginine; 3) a relatively specific neutral amino acid carrier for proline
and alpha-(methylamino)isobutyric acid; and 4) a nonspecific neutral amino
acid system for most other substrates of this group. This scheme for
carnivorous fish intestine most closely approximates that reported for
mammalian gut with minor dissimilarities that may relate to metabolic
differences or specific dietary requirements of the two vertebrate groups.
