Basolateral glucose transport by intestine of teleost, Oreochromis mossambicus

Transport characteristics of D-glucose by isolated basolateral membrane vesicles of the teleost fish, Oreochromis mossambicus, were measured. Specific activity of the vesicle Na-K-adenosinetriphosphatase was increased 11-fold, whereas specific activities of brush-border and organelle membrane enzymes were enriched only 0.3- to 0.8-fold. Vesicles had diameters of 0.1-0.4 micron, 70% of vesicles were leaky (unsealed), and 60% of sealed vesicles were inside out. D-Glucose transport occurred by stereospecific facilitated diffusion, independent of 120 mM gradients of either NaCl or KCl, and was inhibited by sulfhydryl reagents, phloretin, and cytochalasin B, but not by phloridzin. Competition studies with a range of sugars demonstrated that aldohexoses in the C-1 chair conformation were preferred substrates and probably share the same carrier. Kinetic analysis of glucose influx yielded a Kt of 10 mM and a Jmax of 3,910 pmol X mg protein-1 X min-1. Fish intestinal basolateral D-glucose transport closely resembles that of mammalian or avian intestinal epithelia and of red blood cell plasma membrane. The magnitude of transport is much lower in fish than in other vertebrates, which may be related to lower metabolic rates in these poikilotherms.