Effects of endurance training status and sex differences on Na+,K+-pump mRNA expression, content and maximal activity in human skeletal muscle

AIM - This study investigated the effects of endurance training status and sex differences on skeletal muscle Na+,K+-pump mRNA expression, content and activity. METHODS - Forty-five endurance-trained males (ETM), 11 recreationally active males (RAM), and nine recreationally active females (RAF) underwent a vastus lateralis muscle biopsy. Muscle was analysed for Na+,K+-pump alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) isoform mRNA expression (real-time reverse transcription-polymerase chain reaction), content ([H-3]-ouabain-binding site) and maximal activity (3-O-methylfluorescein phosphatase, 3-O-MFPase). RESULTS - ETM demonstrated lower alpha(1), alpha(3), beta(2) and beta(3) mRNA expression by 74%, 62%, 70% and 82%, respectively, than RAM (P < 0.04). In contrast, [H-3]-ouabain binding and 3-O-MFPase activity were each higher in ETM than in RAM, by 16% (P < 0.03). RAM demonstrated a 230% and 364% higher alpha(3) and beta(3) mRNA expression than RAF, respectively (P < 0.05), but no significant sex differences were found for alpha(1), alpha(2), beta(1) or beta(2) mRNA, [H-3]-ouabain binding or 3-O-MFPase activity. No significant correlation was found between years of endurance training and either [H-3]-ouabain binding or 3-O-MFPase activity. Significant but weak correlations were found between the number of training hours per week and 3-O-MFPase activity (r = 0.31, P < 0.02) and between incremental exercise VO2(peak) and both [H-3]-ouabain binding (r = 0.33, P < 0.01) and 3-O-MFPase activity (r = 0.28, P < 0.03). CONCLUSIONS - Isoform-specific differences in Na+,K+-pump mRNA expression were found with both training status and sex differences, but only training status influenced Na+,K+-pump content and maximal activity in human skeletal muscle.