title: Fatigue depresses maximal in vitro skeletal muscle Na(+)-K(+)-ATPase activity in untrained and trained individuals.
abstract: This study investigated whether fatiguing dynamic exercise depresses maximal in vitro Na(+)-K(+)-ATPase activity and whether any depression is attenuated with chronic training. Eight untrained (UT), eight resistance-trained (RT), and eight endurance-trained (ET) subjects performed a quadriceps fatigue test, comprising 50 maximal isokinetic contractions (180 degrees /s, 0.5 Hz). Muscle biopsies (vastus lateralis) were taken before and immediately after exercise and were analyzed for maximal in vitro Na(+)-K(+)-ATPase (K(+)-stimulated 3-O-methylfluoroscein phosphatase) activity. Resting samples were analyzed for [(3)H]ouabain binding site content, which was 16.6 and 18.3% higher (P < 0.05) in ET than RT and UT, respectively (UT 311 +/- 41, RT 302 +/- 52, ET 357 +/- 29 pmol/g wet wt). 3-O-methylfluoroscein phosphatase activity was depressed at fatigue by -13.8 +/- 4.1% (P < 0.05), with no differences between groups (UT -13 +/- 4, RT -9 +/- 6, ET -22 +/- 6%). During incremental exercise, ET had a lower ratio of rise in plasma K(+) concentration to work than UT (P < 0.05) and tended (P = 0.09) to be lower than RT (UT 18.5 +/- 2.3, RT 16.2 +/- 2.2, ET 11.8 +/- 0.4 nmol. l(-1). J(-1)). In conclusion, maximal in vitro Na(+)-K(+)-ATPase activity was depressed with fatigue, regardless of training state, suggesting that this may be an important determinant of fatigue.
authors.affiliation: School of Human Movement, Recreation and Performance, Exercise and Sports Science, Victoria University of Technology, Melbourne, Victoria, 8001, Australia.
authors.forename: Steve F
authors.initials: SF
authors.lastname: Fraser
authors.forename: Jia L
authors.initials: JL
authors.lastname: Li
authors.forename: Michael F
authors.initials: MF
authors.lastname: Carey
authors.forename: Xiao N
authors.initials: XN
authors.lastname: Wang
authors.forename: Termboon
authors.initials: T
authors.lastname: Sangkabutra
authors.forename: Simon
authors.initials: S
authors.lastname: Sostaric
authors.forename: Steve E
authors.initials: SE
authors.lastname: Selig
authors.forename: Keld
authors.initials: K
authors.lastname: Kjeldsen
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McKenna
mesh_terms: D000328:Adult; D001810:Blood Volume / Q000502:physiology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000201:enzymology*; D010101:Oxygen Consumption; D010806:Physical Education and Training; D010807:Physical Endurance / Q000502:physiology; D011188:Potassium / Q000097:blood; D012016:Reference Values; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014891:Weight Lifting / Q000502:physiology
chemical_list: C045349:3-O-methyl-fluorescein phosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium