Intestinal electrogenic sodium-dependent glucose absorption in tilapia and trout reveal species differences inSLC5A-associated kinetic segmental segregation

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Abstract
Electrogenic sodium dependent glucose transport along the length of the intestine was compared between the omnivorous Nile tilapia (Oreochromis niloticus) and the carnivorous Rainbow trout (Oncorhynchus mykiss) in Ussing chambers. In tilapia, a high-affinity, high-capacity (Ha/Hc) kinetic system accounted for the transport throughout the proximal intestine, mid-intestine, and hindgut segments. Similar dapagliflozin and phloridzin dihydrate inhibition across all segments support this homogenous Ha/Hc system throughout the tilapia intestine. Genomic and gene expression analysis supported findings by identifying 10 of the known 12 SLC5A family members, with homogeneous expression throughout the segments with dominant expression of SGLT1 (SLC5A1) and SMIT2 (SLC5A11). In contrast, trout's electrogenic sodium-dependent glucose absorption was 20-35 times lower and segregated into three significantly different kinetic systems found in different anatomical segments. A high-affinity, low-capacity (Ha/Lc) system in the pyloric caeca, a super-high-affinity, low-capacity (sHa/Lc) system in the midgut, and a low-affinity, low-capacity (La/Lc) system in the hindgut. Genomic and gene expression analysis found 5 of the known 12 SLC5A family members with dominant expression of SGLT1 (SLC5A1), SGLT2 (SLC5A2), and SMIT2 (SLC5A11) in the pyloric caeca, and only SGLT1 (SLC5A1) in the midgut, accounting for differences in kinetics between the two. The hindgut presented a La/Lc system partially attributed to a decrease in SGLT1 (SLC5A1). Overall, the omnivorous tilapia had a higher electrogenic glucose absorption than the carnivorous trout, represented with different kinetic systems and a greater expression and number of SLC5A orthologs. Fish differ from mammals having hindgut electrogenic glucose absorption and segment specific transport kinetics.
Funding Information
  • NSERC Discovery (371364-2010)
  • NSERC CRD (CRDPJ: 446912-13)
  • Saskatchewan Pulse Crop Development Board

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