Impaired exercise performance and muscle Na+,K+-pump activity in renal transplantation and haemodialysis patients

Background. We examined whether abnormal skeletal muscle Na+,K+-pumps underlie impaired exercise performance in haemodialysis patients (HDP) and whether these are improved in renal transplant recipients (RTx). Methods. Peak oxygen consumption ((V) over dotO(2peak)) and plasma [K+] were measured during incremental exercise in 9RTx, 10 HDP and 10 healthy controls (CON). Quadriceps peak torque (PT), fatigability (decline in strength during thirty contractions), thigh muscle cross-sectional area (TMCSA) and vastus lateralis Na+,K+-pump maximal activity, content and isoform (alpha(1)-alpha(3), beta(1)-beta(3)) abundance were measured. Results. (V) over dotO(2peak) was 32 and 35% lower in RTx and HDP than CON, respectively (P < 0.05). PT was less in RTx and HDP than CON (P < 0.05) but did not differ when expressed relative to TMCSA. Fatigability was similar to 1.6-fold higher in RTx (24 +/- 11%) and HDP (25 +/- 4%) than CON (15 +/- 5%, P < 0.05). Na+,K+-pump activity was 28 and 31% lower in RTx and HDP, respectively than CON (P < 0.02), whereas content and isoform abundance did not differ. Pooled (n = 28) (V) over dotO(2peak) correlated with Na+,K+-pump activity (r = 0.45, P = 0.02). Conclusions. (V) over dotO(2peak) and muscle Na+,K+-pump activity were depressed and muscle fatigability increased in HDP, with no difference observed in RTx. These findings are consistent with the possibility that impaired exercise performance in HDP and RTx may be partially due to depressed muscle Na+,K+-pump activity and relative TMCSA.