Abstract
PURPOSE: In this study, we investigated the effects of prolonged exercise on muscle Na+-K+-ATPase function in males following dietary CHO manipulation. METHODS: Seven healthy male volunteers (VO2peak = 39.2 ± 1.8 mL/kg/min) cycled at ∼65% of their peak aerobic power (VO2peak) on two occasions; namely following a 4-day high CHO diet (Hi CHO) and following a 4-day low CHO diet (Lo CHO). A glycogen depletion protocol was completed prior to each condition. Muscle samples from the vastus lateralis were collected at rest, 30 min of exercise, Lo CHO fatigue, and Hi CHO fatigue. Maximal Na+-K+-ATPase activity (Vmax) was assessed using the 3-O-methylfluorescein phosphatase assay while the maximal number of alpha subunits (βmax) was measured using the [3H] ouabain binding technique. RESULTS: In Lo CHO, Vmax (nmole/mg protein/h) was reduced (p<.05) at 30 min (71 ± 3) but not at Lo CHO fatigue (80 ± 10) compared to rest (87 ± 6). A similar pattern was observed for Hi CHO, namely a reduction (p<.05) at 30 min (70 ± 7) and no change at Lo CHO fatigue (94 ± 6) compared to rest (88 ± 14). No further change was found at Hi CHO fatigue (104 ± 7). Although no differences in Vmax were observed between Lo CHO and Hi CHO at similar time points, Vmax was higher (p<.05) at fatigue in Hi CHO compared to Lo CHO. Time to fatigue in Hi CHO (103 ± 9.3 min) increased by 54% compared to Lo CHO (66.7 ± 5.9 min). Increases (p<.05) in βmax (pmol/g) from rest to fatigue were observed in Lo CHO (291 ± 15 vs. 316 ± 19) and Hi CHO (311 ± 21 vs. 336 ± 9). There was a trend (p=.07) for βmax to be higher in Hi CHO compared to Lo CHO. Total muscle glycogen (mmol glucosyl units/kg dry wt) was higher (P < 0.05) in Hi CHO compared with Lo CHO at rest (+36%), at 30 min (+53%), and at Lo CHO fatigue (+44%). CONCLUSIONS: These changes in Vmax with exercise suggest that 2 mechanisms are involved, one that depresses Vmax early in exercise and one that restores Vmax as exercise progresses. Manipulation of muscle glycogen levels did not alter the response. The increase in α subunit abundance observed at fatigue suggests a translocation to the sarcolemma, an effect which may be potentiated by Hi CHO. Supported by NSERC (Canada)
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
