title: Creatine transporter activity and content in the rat heart supplemented by and depleted of creatine.
abstract: The intracellular creatine concentration is an important bioenergetic parameter in cardiac muscle. Although creatine uptake is known to be via a NaCl-dependent creatine transporter (CrT), its localization and regulation are poorly understood. We investigated CrT kinetics in isolated perfused hearts and, by using cardiomyocytes, measured CrT content at the plasma membrane or in total lysates. Rats were fed control diet or diet supplemented with creatine or the creatine analog beta-guanidinopropionic acid (beta-GPA). Creatine transport in control hearts followed saturation kinetics with a K(m) of 70 +/- 13 mM and a V(max) of 3.7 +/- 0.07 nmol x min(-1) x g wet wt(-1). Creatine supplementation significantly decreased the V(max) of the CrT (2.7 +/- 0.17 nmol x min(-1) x g wet wt(-1)). This was matched by an approximately 35% decrease in the plasma membrane CrT; the total CrT pool was unchanged. Rats fed beta-GPA exhibited a >80% decrease in tissue creatine and increase in beta-GPA(total). The V(max) of the CrT was increased (6.0 +/- 0.25 nmol x min(-1) x g wet wt(-1)) and the K(m) decreased (39.8 +/- 3.0 mM). The plasma membrane CrT increased about fivefold, whereas the total CrT pool remained unchanged. We conclude that, in heart, creatine transport is determined by the content of a plasma membrane isoform of the CrT but not by the total cellular CrT pool.
authors.affiliation: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, United Kingdom. ernie.boehm@bioch.ox.ac.uk
authors.forename: Ernest
authors.initials: E
authors.lastname: Boehm
authors.forename: Sharon
authors.initials: S
authors.lastname: Chan
authors.forename: Mina
authors.initials: M
authors.lastname: Monfared
authors.forename: Theo
authors.initials: T
authors.lastname: Wallimann
authors.forename: Kieran
authors.initials: K
authors.lastname: Clarke
authors.forename: Stefan
authors.initials: S
authors.lastname: Neubauer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D019921:Biotinylation; D001835:Body Weight; D003401:Creatine / Q000097:blood / Q000172:deficiency / Q000493:pharmacokinetics*; D003402:Creatine Kinase / Q000378:metabolism; D006146:Guanidines / Q000097:blood / Q000493:pharmacokinetics; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D009929:Organ Size; D010477:Perfusion; D011422:Propionates / Q000097:blood / Q000493:pharmacokinetics; D051381:Rats; D017208:Rats, Wistar
chemical_list: D006146:Guanidines; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011422:Propionates; C080679:creatine transporter; D000255:Adenosine Triphosphate; D003402:Creatine Kinase; D003401:Creatine; C005775:guanidinopropionic acid