Metabolic acidosis in sheep alters expression of renal and skeletal muscle amino acid enzymes and transporters

• Published in: Journal of animal science Vol. 88; no. 2; pp. 707 - 717
• Main Authors: Xue, Y, Liao, S.F, Son, K.W, Greenwood, S.L, McBride, B.W, Boling, J.A, Matthews, J.C
• Format: Journal Article
• Language: English
• Published: Champaign, IL American Society of Animal Science 01-02-2010; Am Soc Animal Sci
• Subjects: Acidosis - enzymology; Acidosis - metabolism; Acidosis - veterinary; Amino Acid Transport Systems - metabolism; amino acid transporters; Amino Acids - metabolism; Animal productions; Animals; Aspartate Aminotransferases - metabolism; aspartic acid; Aspartic Acid - metabolism; Biological and medical sciences; complications; diet-related diseases; enzyme activity; enzymes; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Enzymologic; glutamic acid; glutamine; Glutamine - metabolism; Immunoblotting; Kidney - enzymology; Kidney - metabolism; kidneys; Muscle, Skeletal - enzymology; Muscle, Skeletal - metabolism; polymerase chain reaction; protein synthesis; renal function; Reverse Transcriptase Polymerase Chain Reaction; ruminal acidosis; sheep; Sheep - metabolism; sheep diseases; Sheep Diseases - enzymology; Sheep Diseases - metabolism; skeletal muscle; Terrestrial animal productions; Vertebrates; Farming animal; Enzyme; amino acid; Transferases; coupled neutral amino acid transporter; Metabolism; Vertebrata; Meat animals; Mammalia; Na; Transaminases; acidosis; Aspartate transaminase; Sheep; Muscle; Artiodactyla; Ungulata; Metabolic acidosis
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2009-2101

To determine the effect of metabolic acidosis on expression of L-Gln, L-Glu, and L-Asp metabolizing enzymes and transporters, the relative content of mRNA, protein, or mRNA and protein, of 6 enzymes and 5 transporters was determined by real-time reverse transcription-PCR and immunoblot analyses in homogenates of kidney, skeletal muscle, and liver of growing lambs fed a common diet supplemented with canola meal (control; n = 5) or HCl-treated canola meal (acidosis; n = 5). Acidotic sheep had a 790% greater (P = 0.050) expression of renal Na⁺-coupled neutral AA transporter 3 mRNA and a decreased expression of renal glutamine synthetase mRNA (47% reduction, P = 0.037) and protein (57% reduction, P = 0.015) than control sheep. No change in renal cytosolic phosphoenolpyruvate carboxykinase (protein and mRNA), glutaminase (mRNA), or L-Glu dehydrogenase (protein) was found. In skeletal muscle, acidotic sheep had 101% more (P = 0.026) aspartate transaminase protein than did control sheep, whereas no change in the content of 3 Na⁺-coupled neutral AA transporters (mRNA) or 2 high-affinity L-Glu transporter proteins was found. In liver, no change in the content of any assessed enzyme or transporter was found. Collectively, these findings suggest that tissue-level responses of sheep to metabolic acidosis are different than for nonruminants. More specifically, these results indicate the potential capacity for metabolism of L-Asp and L-Glu by skeletal muscle, and L-Gln absorption by kidneys, but no change in hepatic expression of L-Gln metabolism, elaborates previous metabolic studies by revealing molecular-level responses to metabolic acidosis in sheep. The reader is cautioned that the metabolic acidosis model employed in this study differs from the increased plasma lactate-induced metabolic acidosis commonly observed in ruminants fed a highly fermentable grain diet.