title: Competition for transport of amino acids into rat heart: effect of competitors on protein synthesis and degradation.
abstract: Transport of the neutral amino acids, 2-(methylamino)isobutyrate (MeAIB) and Phe, was examined in isolated rat hearts perfused by the Langendorff method. Hearts were perfused by recirculating for various time periods buffer containing [14C]-MeAIB or [14C]-Phe plus desired additions. Uptake of MeAIB was linear for approximately 30 minutes; Phe uptake was linear for a maximum of 5 minutes, and reached a steady state after 15 minutes. Km and Vmax for MeAIB were 1.1 +/- 0.03 mmol/L and 37.7 +/- 0.4 pmol/microL intracellular fluid (ICF)/min; values for Phe were 1.8 +/- 0.02 mmol/L and 364 +/- 5 pmol/microL ICF/minute. Uptake of MeAIB (0.2 mmol/L) was reduced 95% in the presence of Ser (10 mmol/L), and less severely by large neutral amino acids ([LNAA], 10 mmol/L) such as Phe and Leu (by 46% and 54%, respectively). Uptake of Phe (0.2 mmol/L) was reduced by LNAA such as Val, Leu, and Ile (by 51%, 78%, and 81%, respectively), or by commercial preparations used in parenteral nutrition, eg, Travasol or Travasol plus extra branched-chain amino acids (BCAA) (Branchamin); Ser had little effect (8% reduction). Insulin in the perfusion medium increased the fractional rate of protein synthesis. Individual BCAA at physiological concentrations (0.2 mmol/L) did not alter the rate of protein synthesis. Branchamin or Travasol plus Branchamin also had no effect on the rate of protein synthesis in heart, but did depress the rate of degradation. These studies suggest that amino acid transport into heart may be affected by normal levels of plasma amino acids, whereas protein synthesis is not.
authors.affiliation: Department of Nutritional Sciences, University of Wisconsin-Madison.
authors.forename: A R
authors.initials: AR
authors.lastname: Tovar
authors.forename: J K
authors.initials: JK
authors.lastname: Tews
authors.forename: N
authors.initials: N
authors.lastname: Torres
authors.forename: D C
authors.initials: DC
authors.lastname: Madsen
authors.forename: A E
authors.initials: AE
authors.lastname: Harper
mesh_terms: D000596:Amino Acids / Q000378:metabolism / Q000493:pharmacokinetics* / Q000494:pharmacology*; D000597:Amino Acids, Branched-Chain / Q000493:pharmacokinetics / Q000494:pharmacology*; D000621:Aminoisobutyric Acids / Q000032:analysis / Q000493:pharmacokinetics; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002250:Carbon Radioisotopes; D004573:Electrolytes; D005947:Glucose; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D007328:Insulin / Q000494:pharmacology*; D007930:Leucine / Q000378:metabolism / Q000493:pharmacokinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D057947:Parenteral Nutrition Solutions; D010477:Perfusion; D010649:Phenylalanine / Q000378:metabolism / Q000493:pharmacokinetics; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012694:Serine / Q000494:pharmacology; D012996:Solutions; D013997:Time Factors
chemical_list: D000596:Amino Acids; D000597:Amino Acids, Branched-Chain; D000621:Aminoisobutyric Acids; D002250:Carbon Radioisotopes; D004573:Electrolytes; D007328:Insulin; D057947:Parenteral Nutrition Solutions; D011506:Proteins; D012996:Solutions; C545824:amino-acid, glucose, and electrolyte solution; C017911:2-(methylamino)isobutyric acid; D012694:Serine; D010649:Phenylalanine; D007930:Leucine; D005947:Glucose