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.

Post-Match Changes in Muscle Damage Markers among U-21 Soccer Players

“…However, the plasma [Na + ] concentration was unchanged aft er an offi cial soccer match in U-21 players, which is in line with Takarada (2003). Fraser et al (2002) observed reduced maximal activity of the Na + /K + pump following diff erent types of exercise. While these plasma values do not provide a clear picture of the concentrations around the contracting muscle fi bres in soccer (Bangsbo, Mohr, & Krustrup, 2006), further research is needed to reveal what may cause fatigue during a soccer game.…”

Muscle Na-K-pump and fatigue responses to progressive exercise in normoxia and hypoxia

“…Both our group (19) and others (22) have reported decreases in maximal Na ϩ -K ϩ -ATPase activity, as assessed in vitro by K ϩ -stimulated 3-Omethylfluorescein phosphatase (3-O-MFPase), after exercise. As a consequence, it is possible that the Na ϩ -K ϩ -membrane transport and membrane excitability would be compromised in tasks in which large force levels are required.…”

Dissociation between force and maximal Na+, K+-ATPase activity in rat fast-twitch skeletal muscle with fatiguing in vitro stimulation

“…This measure correlates well with the [ 3 H]ouabain binding site content in whole muscle and biopsy samples (Fraser et al 2002;Norgaard et al 1984) is sensitive to ouabain inhibition (Fraser et al 2002;Norgaard et al 1984) and was increased proportionately with [ 3 H]ouabain binding sites with dexamethasone (Nordsborg et al 2005), and as such is considered to be a valid measure of NKA activity (McKenna et al 2008).…”

“…A remarkably consistent Wnding in human skeletal muscle is that acute exercise depressed the maximal 3-OMFPase activity by »11-35% (mean »18%); this occurred in 13 out of 14 human exercise studies, that utilized various exercise modes, durations and intensities (Aughey et al , 2006(Aughey et al , 2007Fowles et al 2002a;Fraser et al 2002;Green et al 2007a, b;Green et al 2008;Leppik et al 2004;McKenna et al 2006;Murphy et al 2006a;Petersen et al 2005;Sandiford et al 2004Sandiford et al , 2005a These reductions in maximal 3-O-MFPase activity have been interpreted as a reduction in the maximal attainable in vivo NKA activation which may contribute to reduced excitability and thus muscle fatigue during exercise (Fowles et al 2002a;Fraser et al 2002;McKenna et al 2008).…”