Low-load blood flow restriction training and ischemia modulate expression of Na+,K+-ATPase and FXYDs in human skeletal muscle.

Anterior cruciate ligament (ACL) rupture leads to muscle deconditioning and downregulation of Na+,K+-ATPase (NKA). Low-load blood flow restriction (LL-BFR) training was shown to improve muscle function after ACL injury, but its effects on NKA are unknown. We analysed expression of NKA and its FXYD regulators in knee muscles from ACL-injured subjects undergoing LL-BFR, low-load training with sham blood flow restriction (LL-Sham), or no training (Control). Additionally, we dissected effects of ischemia components by subjecting cultured human myotubes to glucose deprivation and/or hypoxia. The LL-BFR group had higher vastus lateralis mRNA levels of NKAα1 than the Control and LL-Sham groups. In vitro, NKAα1, NKAβ1, and NKAβ3 mRNA and NKAα1 and NKAβ1 protein levels were downregulated by sustained ischemia and glucose deprivation, but not hypoxia, while FXYD5 protein was upregulated by glucose deprivation. Conversely, intermittent ischemia had no effect on NKA or FXYD expression. In conclusion, LL-BFR training was associated with upregulation of NKAα1 mRNA levels in the vastus lateralis after ACL injury; however, in the absence of corresponding changes in protein abundance, its contribution to functional recovery remains unclear. Moreover, our in vitro findings suggest that glucose availability plays a major role in modulating NKA and FXYD expression in muscle cells under ischemic conditions.