Publications by authors named "Marina Subramaniam"

5 Publications

  • Page 1 of 1

Glycemic, insulinemic and methylglyoxal postprandial responses to starches alone or in whole diets in dogs versus cats: Relating the concept of glycemic index to metabolic responses and gene expression.

Comp Biochem Physiol A Mol Integr Physiol 2021 Jul 30;257:110973. Epub 2021 Apr 30.

Toxicology Graduate Program, University of Saskatchewan, Saskatoon, SK S7N 5B3, Canada; Veterinary Biomedical Sciences, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada. Electronic address:

Species differences between domestic cats (Felis catus) and dogs (Canis familiaris) has led to differences in their ability to digest, absorb and metabolize carbohydrates through poorly characterized mechanisms. The current study aimed to first examine biopsied small intestine, pancreas, liver and skeletal muscle from laboratory beagles and domestic cats for mRNA expression of key enzymes involved in starch digestion (amylase), glucose transport (sodium-dependent SGLTs and -independent glucose transporters, GLUT) and glucose metabolism (hexokinase and glucokinase). Cats had lower mRNA expression of most genes examined in almost all tissues compared to dogs (p < 0.05). Next, postprandial glucose, insulin, methylglyoxal (a toxic glucose metabolite) and d-lactate (metabolite of methylglyoxal) after single feedings of different starch sources were tested in fasted dogs and cats. After feeding pure glucose, peak postprandial blood glucose and methylglyoxal were surprisingly similar between dogs and cats, except cats had a longer time to peak and a greater area under the curve consistent with lower glycolytic enzyme expression. After feeding starches or whole diets to dogs, postprandial glycemic response, glycemic index, insulin, methylglyoxal and d-lactate followed reported glycemic index trends in humans. In contrast, cats showed very low to negligible postprandial glycemic responses and low insulin after feeding different starch sources, but not whole diets, with no relationship to methylglyoxal or d-lactate. Thus, the concept of glycemic index appears valid in dogs, but not cats. Differences in amylase, glucose transporters, and glycolytic enzymes are consistent with species differences in starch and glucose handling between cats and dogs.
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http://dx.doi.org/10.1016/j.cbpa.2021.110973DOI Listing
July 2021

Characterization of the segmental transport mechanisms of DL-methionine hydroxy analogue along the intestinal tract of rainbow trout with an additional comparison to DL-methionine.

Comp Biochem Physiol A Mol Integr Physiol 2020 11 24;249:110776. Epub 2020 Jul 24.

Veterinary Biomedical Sciences, University of Saskatchewan, Saskatoon, SK, Canada. Electronic address:

The aim of this study was to identify the unknown transport mechanism of the extensively used monocarboxylate methionine feed supplement DL-methionine hydroxy analogue (DL-MHA) in rainbow trout intestine. Transport across the pyloric caeca (PC), midgut (MG), and hindgut (HG) regions were kinetically studied in Na- and H-dependent manners. Gene expression of monocarboxylate (MCTs) and sodium monocarboxylate transporters (SMCTs) were assessed. Results demonstrated that DL-MHA transport from 0.2-20 mM was Na-dependent and obeyed Michaelis-Menten kinetics with low affinity in PC & MG in apical/basal pH of 7.7/7.7. Changes in apical/basal pH (6.0/6.0, 6.0/7.7, and 7.7/8.7) had insignificant effects on kinetics. In contrast, HG flux kinetics were only obtained in pH 7.7/8.7 or in the presence of lactate with medium affinity. Additionally, DL-MHA transport from 0-150 μM demonstrated the presence of a Na-dependent high-affinity transporter in PC & MG. Conclusively, two distinct carrier-mediated DL-MHA transport mechanisms along the trout gut were found: 1) in PC & MG: apical transport was regulated by Na-requiring systems that possibly contained low- and high-affinity transporters, and basolateral transport was primarily achieved through a H-independent transporter; 2) in HG: uptake was apically mediated by a Na-dependent transporter with medium affinity, and basolateral exit was largely controlled by an H-dependent transporter. Finally, two major methionine feed supplements, DL-MHA and DL-methionine (DL-Met) were compared to understand the differences in their bioefficacy. Flux rates of DL-MHA were only about 42.2-66.0% in PC and MG compared to DL-Met, suggesting intestinal transport of DL-MHA was lower than DL-Met.
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http://dx.doi.org/10.1016/j.cbpa.2020.110776DOI Listing
November 2020

Comparison of intestinal glucose flux and electrogenic current demonstrates two absorptive pathways in pig and one in Nile tilapia and rainbow trout.

Am J Physiol Regul Integr Comp Physiol 2020 02 20;318(2):R245-R255. Epub 2019 Nov 20.

Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.

The mucosal-to-serosal flux of C 3--methyl-d-glucose was compared against the electrogenic transport of d-glucose across ex vivo intestinal segments of Nile tilapia, rainbow trout, and pig in Ussing chambers. The difference in affinities ( "fingerprints") between pig flux and electrogenic transport of glucose, and the absence of this difference in tilapia and trout, suggest two absorptive pathways in the pig and one in the fish species examined. More specifically, the total mucosal-to-serosal flux revealed a super high-affinity, high-capacity (sHa/Hc) total glucose transport system in tilapia; a super high-affinity, low-capacity (sHa/Lc) total glucose transport system in trout and a low-affinity, low-capacity (La/Lc) total glucose transport system in pig. Comparatively, electrogenic glucose absorption revealed similar in both fish species, with a super high-affinity, high capacity (sHa/Hc) system in tilapia; a super high-affinity/super low-capacity (sHa/sLc) system in trout; but a different fingerprint in the pig, with a high-affinity, low-capacity (Ha/Lc) system. This was supported by different responses to inhibitors of sodium-dependent glucose transporters (SGLTs) and glucose transporter type 2 (GLUT2) administered on the apical side between species. More specifically, tilapia flux was inhibited by SGLT inhibitors, but not the GLUT2 inhibitor, whereas trout lacked response to inhibitors. In contrast, the pig responded to inhibition by both SGLT and GLUT2 inhibitors with a higher expression of GLUT2. Altogether, it would appear that two pathways are working together in the pig, allowing it to have continued absorption at high glucose concentrations, whereas this is not present in both tilapia and trout.
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http://dx.doi.org/10.1152/ajpregu.00160.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7052593PMC
February 2020

Sigmoidal kinetics define porcine intestinal segregation of electrogenic monosaccharide transport systems as having multiple transporter population involvement.

Physiol Rep 2019 05;7(9):e14090

Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.

Kinetic characterization of electrogenic sodium-dependent transport in Ussing chambers of d-glucose and d-galactose demonstrated sigmoidal/Hill kinetics in the porcine jejunum and ileum, with the absence of transport in the distal colon. In the jejunum, a high-affinity, super-low-capacity (Ha/sLc) kinetic system accounted for glucose transport, and a low-affinity, low-capacity (La/Lc) kinetic system accounted for galactose transport. In contrast, the ileum demonstrated a high-affinity, super-high-capacity (Ha/sHc) glucose transport and a low-affinity, high-capacity (La/Hc) galactose transport systems. Jejunal glucose transport was not inhibited by dapagliflozin, but galactose transport was inhibited. Comparatively, ileal glucose and galactose transport were both sensitive to dapagliflozin. Genomic and gene expression analyses identified 10 of the 12 known SLC5A family members in the porcine jejunum, ileum, and distal colon. Dominant SGLT1 (SLC5A1) and SGLT3 (SLC5A4) expression was associated with the sigmoidal Ha/sLc glucose and La/Lc galactose transport systems in the jejunum. Comparatively, the dominant expression of SGLT1 (SLC5A1) in the ileum was only associated with Ha glucose and La galactose kinetic systems. However, the sigmoidal kinetics and overall high capacity (Hc) of transport is unlikely accounted for by SGLT1 (SLC5A1) alone. Finally, the absence of transport and lack of pharmacological inhibition in the colon was associated with the poor expression of SLC5A genes. Altogether, the results demonstrated intestinal segregation of monosaccharide transport fit different sigmoidal kinetic systems. This reveals multiple transporter populations in each system, supported by gene expression profiles and pharmacological inhibition. Overall, this work demonstrates a complexity to transporter involvement in intestinal electrogenic monosaccharide absorption systems not previously defined.
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http://dx.doi.org/10.14814/phy2.14090DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6503033PMC
May 2019

Intestinal electrogenic sodium-dependent glucose absorption in tilapia and trout reveal species differences in SLC5A-associated kinetic segmental segregation.

Am J Physiol Regul Integr Comp Physiol 2019 03 2;316(3):R222-R234. Epub 2019 Jan 2.

Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan , Saskatoon, Saskatchewan , Canada.

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 kinetic system accounted for the transport throughout the proximal intestine, midintestine, and hindgut segments. Similar dapagliflozin and phloridzin dihydrate inhibition across all segments support this homogenous high-affinity, high-capacity 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 sodium-glucose cotransporter 1 (SGLT1; SLC5A1) and sodium-myoinositol cotransporter 2 (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 system in the pyloric ceca; a super-high-affinity, low-capacity system in the midgut; and a low-affinity, low-capacity system in the hindgut. Genomic and gene expression analysis found 5 of the known 12 SLC5A family members with dominant expression of SGLT1 ( SLC5A1), sodium-glucose cotransporter 2 (SGLT2; SLC5A2), and SMIT2 ( SLC5A11) in the pyloric ceca, and only SGLT1 ( SLC5A1) in the midgut, accounting for differences in kinetics between the two. The hindgut presented a low-affinity, low-capacity 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.
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http://dx.doi.org/10.1152/ajpregu.00304.2018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6459381PMC
March 2019