Metabolic acidosis in sheep alters expression of renal and skeletal muscle amino acid enzymes and transporters.
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.
Xue
Y
Y
Department of Animal and Food Sciences, University of Kentucky, Lexington, Kentucky 40546, USA.
Liao
S F
SF
Son
K W
KW
Greenwood
S L
SL
McBride
B W
BW
Boling
J A
JA
Matthews
J C
JC
D000138:Acidosis / Q000201:enzymology / Q000378:metabolism / Q000662:veterinary*; D026905:Amino Acid Transport Systems / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001219:Aspartate Aminotransferases / Q000378:metabolism; D001224:Aspartic Acid / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005973:Glutamine / Q000378:metabolism; D015151:Immunoblotting; D007668:Kidney / Q000201:enzymology* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012756:Sheep / Q000378:metabolism; D012757:Sheep Diseases / Q000201:enzymology / Q000378:metabolism*
D026905:Amino Acid Transport Systems; D000596:Amino Acids; D005973:Glutamine; D001224:Aspartic Acid; D001219:Aspartate Aminotransferases