Brush-border inositol transport by intestines of carnivorous and herbivorous teleosts.
Transport characteristics of myoinositol by isolated brush-border membrane vesicles of two fish, the herbivorous tilapia (Oreochromis mossambicus) and the carnivorous eel (Anguilla anguilla), were measured. [3H]myoinositol uptake by vesicles of both fish was stimulated by a transmembrane Na gradient, was electrogenic, and was inhibited by phloridzin. Kinetic analysis of myoinositol influx disclosed species differences (tilapia, K = 0.15 mM, Jmax = 0.2 nmol.mg protein-1.min-1; eel, K = 2.6 mM, Jmax = 0.8 nmol.mg protein-1.min-1). D-glucose inhibition of myoinositol influx was shown to be noncompetitive. Additional inhibition studies with a range of sugars demonstrated that aldohexoses in the C-1 chair conformation were preferred substrates. Myoinositol had no effect on D-glucose transport. Preloading vesicles with myoinositol transstimulated [3H]myoinositol uptake, while the use of internal D-glucose was without effect. These results suggest that the intestinal brush border may have a pathway for myoinositol transport entirely separate from that for D-glucose but inhibited by D-glucose via binding to a regulator site on the myoinositol transporter. Markedly dissimilar influx kinetic constants suggest possible differences in myoinositol needs by carnivorous and herbivorous fish.
Vilella
S
S
Departimento di Biologia, Universita di Lecce, Italy.
Reshkin
S J
SJ
Storelli
C
C
Ahearn
G A
GA
D000811:Anguilla / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002241:Carbohydrates / Q000494:pharmacology; D004032:Diet; D005399:Fishes / Q000378:metabolism*; D007294:Inositol / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*
D002241:Carbohydrates; D007294:Inositol