AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 3 463-R469, Copyright © 1986 by American Physiological Society
Na-dependent D-glucose and L-alanine transport in eel intestinal brush border membrane vesicles
C. Storelli, S. Vilella and G. Cassano
Brush border membrane vesicles (BBMV) were prepared from eel (Anguilla
anguilla) intestine by a
Mg-ethylene-glycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid
precipitation technique; the BBMV were enriched 16, 12, and 13 times in
leucine aminopeptidase, maltase, and alkaline phosphatase activities with
respect to the starting mucosal scraping. D-[3H]glucose and L-[3H]alanine
transport by these vesicles was studied by a rapid filtration technique.
D-Glucose uptake was stimulated by a transmembrane Na gradient but not by
an identical Na gradient in the presence of phloridzin or by a choline
gradient. The Na-dependent D-glucose uptake was increased by rendering the
vesicle interior electrically negative, suggesting electrogenic cotransport
of the sugar with Na+. Kinetic analysis gave an apparent affinity constant
(Kapp) of 0.20 mM and maximal rate (Jmax) of 6.87 nmol X mg protein-1 X
min-1 for glucose influx in the presence of a Na gradient. In addition, a
significant apparent diffusional permeability of these membranes to glucose
(1.41 microliters X mg protein-1 X min-1) was observed. L-Alanine uptake in
eel BBMV was shown to occur via 1) saturable Na-dependent pathway (Kapp =
1.29 mM, Jmax = 3.61 nmol X mg protein-1 X min-1), 2) a saturable
Na-independent pathway (Kapp = 0.59, Jmax = 1.49), and 3) a nonsaturable
component representing apparent diffusion (permeability coefficient P =
0.57 microliter X mg protein-1 X min-1). These findings suggest that
similar transport systems for glucose and alanine are found in the fish and
mammalian intestinal brush border membrane.
