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    • Article

      Intestinal glucose transport in carnivorous and herbivorous marine fishes 

      RP Ferraris & GA Ahearn - Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology, 1983 - Springer Verlag
      The influx and transepithelial movements of glucose and their effects on the electrophysiology and Na transport in upper and lower intestines of the herbivorous surgeonfish, Acanthurus mata , and carnivorous eel, Gymnothorax undulatus , were measured. The K t G and J max G of glucose influx into the tissues were higher in the surgeonfish upper intestine than in the surgeonfish lower intestine or in both segments of the eel intestine. A prominent diffusion-like transport component was also measured in all four segments during influx experiments. Net transepithelial glucose fluxes (0.05 mM) were greater in eel intestine than in those of the surgeonfish largely due to an apparent lower apical membrane permeability of the former coincident with reduced backflux of glucose from epithelium to lumen. All four stripped intestinal segments exhibited non-significant (from zero; P >0.05) or small, serosa-negative transepithelial potential differences (-0.1 to -2.2 mV), and low transepithelial resistances (40–88 O cm -2 ). Each tissue displayed significant ( P P >0.05) change the transepithelial resistance, but did induce a significant ( P J net Na with added luminal glucose, these increased net cation fluxes were not quite significant ( P >0.05). It is concluded that coupled Na-glucose transport occurs in these tissues, but that metabolic enhancement of unrelated current-generating mechanisms also takes place and may modify depolarizing effects of organic solute transfer.
    • Article

      Sugar and amino acid transport in fish intestine 

      RP Ferraris & GA Ahearn - Comparative Biochemistry and Physiology - Part A: Physiology, 1984 - Elsevier
      1. Morphological properties of fish intestines vary with diet. Carnivores have short guts with highly elaborate mucosal folding in the upper intestines; herbivores have long guts which appear structurally uniform from stomach to rectum.

      2. Brush border membranes of many fish intestines display at least two transport processes for each organic solute, one an Na+-dependent, saturable carrier mechanism, and the other a non-saturable influx pathway which may be simple diffusion.

      3. Intestinal epithelial cells from freshwater fish can accumulate nutrients to concentrations in excess of those in the gut lumen; those of marine fish can not.

      4. Net transepithelial nutrient transport in upper intestine is greater in freshwater fish than in marine forms as a result of considerable solute backflux from epithelium to lumen in the latter.

      5. In many fish the lower intestine displays a significant net transmural flux of nutrients that may contribute to total organic solute absorption.

      6. Intestines of freshwater fish have a serosa positive (relative to mucosa) electrical potential difference; marine fish display a negative serosa.

      7. Addition of organic solutes to intestines of freshwater fish hyperpolarizes the electrically positive serosa; in marine forms a depolarization of the serosa negative potential occurs. In both cases this appears due to increased net transmural sodium transport coupled to net nutrient flow.