title: Skeletal muscle Na(+)-K(+)-ATPase and K+ homeostasis during exercise: effects of short-term training.
abstract: The objective of this study was to determine the effects of 10 consecutive days of moderate intensity training on 1) the concentration of middle gluteal muscle Na(+)-K(+)-ATPase as determined by vanadate-facilitated 3H[ouabain binding; and 2) plasma potassium regulation before, during and after exercise at 100% of the pre-training maximum rate of oxygen consumption (VO2max). Six mature, unfit Thoroughbred horses completed both incremental (for determination of VO2max) and high-intensity exercise protocols before (HI1) and after (HI2) training. There additional horses undertook no training or exercise tests and served as controls for determination of middle gluteal muscle Na(+)-K(+)-ATPase concentration. Training consisted of 10 consecutive days of running at 55% VO2max for 60 min per day (13-14 km/day). For each high intensity exercise protocol, horses completed a 10 min warm-up at 50% VO2max, followed by exercise at 100% of pre-training VO2max (6 degrees incline, mean speed 9.8 m/s) until fatigue. Training resulted in a 13.8% increase in resting plasma volume (pre: 20.9 +/- 0.8 l; post: 23.8 +/- 0.9 l; P = 0.03), and an 8.9% increase in VO2max (pre: 142 +/- 4 ml/kg/min; post: 155 +/- 4 ml/kg/min; P = 0.004) during HI. Peak values for plasma potassium concentration and content during exercise decreased by 13% (P = 0.02) and 7% (P = 0.0002), respectively, after training whereas training had no effect on increases in packed cell volume, plasma total solids, and erythrocyte K+ concentration and content during exercise. Following training, there was also a significant (23%) increase in Na(+)-K(+)-ATPase concentration in biopsies of middle gluteal muscle, as measured by vanadate-facilitated 3H[ouabain binding. We conclude that 10 days of moderate intensity exercise results in increases in skeletal muscle Na(+)-K(+)-ATPase and attenuation in the elevation in plasma K+ during high intensity exercise at the same absolute workload. The increase in middle gluteal muscle Na(+)-K(+)-ATPase concentration is consistent with decreases in K+ efflux from working muscle during exercise.
authors.affiliation: Department of Pathobiology, Ontario Veterinary College, University of Guelph, Canada.
authors.forename: L J
authors.initials: LJ
authors.lastname: McCutcheon
authors.forename: R J
authors.initials: RJ
authors.lastname: Geor
authors.forename: H
authors.initials: H
authors.lastname: Shen
mesh_terms: D000818:Animals; D001810:Blood Volume; D005260:Female; D006706:Homeostasis; D006736:Horses / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology*; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium