Na+-d-glucose cotransport by intestinal brush border membrane
vesicles of the antarctic fish trematomus bernacchii.
Maffia, M., R. Acierno, E. Cillo, C. Storelli.
Laboratorio di Fisiologia Generale, Dipartimento di Biologia,
Universit[grave]a di Lecce, 73100 Lecce, Italy
APStracts 3:0142R, 1996.
Intestinal nutrient absorption in fish adapted to low temperature was
investigated by isolating, with a Mg2+-precipitation procedure,
brush-border membrane vesicles from the intestine of the Antarctic
teleost Trematomus bernacchii. In particular D-glucose transport was
analysed by measuring both: 1) the fluorescence changes of the
electrical potential sensitive dye DiS-C2(5); 2) the intravesicular
uptake of D-[14C]-glucose. Results demonstrated that the transport of
D-glucose across the intestinal brush border membranes of the
Antarctic fish is stimulated by the presence of a transmembrane Na+
gradient (out > in) and was specifically inhibited by
phloridzin. Furthermore the Na+-dependent D-glucose uptake was
strongly enhanced by the presence of an electrical potential (inside
negative) across the membrane. There was a marked difference in the
temperature-dependence of Na+-sugar cotransport between the Antarctic
fish and a temperate fish as the European yellow eel. Na+-dependent
D-glucose uptake in T. bernacchii intestinal BBMV reached its maximal
rate at -2/0 C (close to the fish living temperature) and was
exponentially inactivated by incubation at higher temperatures. A
kinetic analysis of D-glucose influx indicated the presence of a
single Na-dependent carrier process (Jmax = 0.233 +/- 0.009 nmoles x
mg protein-1 x min-1; Kmapp = 0.157 +/- 0.026 mmoles x l-1) and a
nonsaturable transfer component (P = 0.233 +/- 0.016 [mu]l x mg
protein-1 x min-1). The Na+-dependent carrier mediated mechanism was
specific for sugars since it was partially inhibited by the presence
in the extravesicular medium of other monosaccarides but not by
ascorbic acid or amino acids of different type. These data suggest
that in the intestine of Antarctic fish luminal D-glucose transport
takes place by a specific Na+-dependent electrogenic secondary active
transport working well at subzero temperatures.
Received 20 November 1995; accepted in final form 1 April 1996.
APS Manuscript Number R726-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 23 April 96