title: Effects of training on potassium homeostasis during exercise and skeletal muscle Na+,K(+)-ATPase concentration in young adult and middle-aged Dutch Warmblood horses.
abstract: OBJECTIVE
  To investigate the effects of moderate short-term training on K+ regulation in plasma and erythrocytes during exercise and on skeletal muscle Na+,K(+)-ATPase concentration in young adult and middle-aged horses.
  
  
  METHODS
  Four 4- to 6-year-old and four 10- to 16-year-old Dutch Warmblood horses.
  
  
  METHODS
  The horses underwent a 6-minute exercise trial before and after 12 days of training. Skeletal muscle Na+,K(+)-ATPase concentration was analyzed in gluteus medius and semitendinosus muscle specimens before and after the 12-day training period. Blood samples were collected before and immediately after the trials and at 3, 5, 7, and 10 minutes after cessation of exercise for assessment of several hematologic variables and analysis of plasma and whole-blood K+ concentrations.
  
  
  RESULTS
  After training, Na+,K(+)-ATPase concentration in the gluteus medius, but not semitendinosus, muscle of middle-aged horses increased (32%), compared with pretraining values; this did not affect the degree of hyperkalemia that developed during exercise. The development of hyperkalemia during exercise in young adult horses was blunted (albeit not significantly) without any change in the concentration of Na+,K(+)-ATPase in either of the muscles. After training, the erythrocyte K+ concentration increased (7% to 10%) significantly in both groups of horses but did not change during the exercise trials.
  
  
  CONCLUSIONS
  In horses, the activation of skeletal muscle Na+,K(+)-ATPase during exercise is likely to decrease with age. Training appears to result in an increase in Na+,K(+)-ATPase activity in skeletal muscle with subsequent upregulation of Na+,K(+)-ATPase concentration if the existing Na+,K(+)-ATPase capacity cannot meet requirements.
authors.affiliation: Department of Pathobiology, Anatomy and Physiology, Faculty of Veterinary Medicine, Utrecht University, 3508 TD Utrecht, The Netherlands.
authors.forename: Pisit
authors.initials: P
authors.lastname: Suwannachot
authors.forename: Brian J L J
authors.initials: BJ
authors.lastname: Joosten
authors.forename: Andries
authors.initials: A
authors.lastname: Klarenbeek
authors.forename: Jos
authors.initials: J
authors.lastname: Hofma
authors.forename: Edwin
authors.initials: E
authors.lastname: Enzerink
authors.forename: P René
authors.initials: PR
authors.lastname: van Weeren
authors.forename: Maria E
authors.initials: ME
authors.lastname: Everts
mesh_terms: D000375:Aging / Q000378:metabolism; D000818:Animals; D006706:Homeostasis; D006736:Horses / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011188:Potassium / Q000097:blood / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium