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

<b>Aim</b>: This study investigated the effects of endurance training status and sex differences on skeletal muscle Na⁺,K⁺-pump mRNA expression, content and activity. <b>Methods</b>: 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 α1, α2, α3, β1, β2 and β3 isoform mRNA expression (real-time reverse transcription-polymerase chain reaction), content ([³H]-ouabain-binding site) and maximal activity (3-O-methylfluorescein phosphatase, 3-O-MFPase). <b>Results</b>: ETM demonstrated lower α1, α3, β2 and β3 mRNA expression by 74%, 62%, 70% and 82%, respectively, than RAM (<i>P</i> < 0.04). In contrast, [³H]-ouabain binding and 3-O-MFPase activity were each higher in ETM than in RAM, by 16% (<i>P</i> < 0.03). RAM demonstrated a 230% and 364% higher α3 and b3 mRNA expression than RAF, respectively (P < 0.05), but no significant sex differences were found for α1, α2, β1 or β2 mRNA, [³H]-ouabain binding  or 3-O-MFPase activity. No significant correlation was found between years of endurance training and either [³H]-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 (<i>r</i> = 0.31, <i>P</i> < 0.02) and between incremental exercise<b> V</b> O_2(peak) and both   [³H]-ouabain binding (<i>r</i> = 0.33, <i>P</i> < 0.01) and 3-O-MFPase activity (<i>r</i> = 0.28, <i>P </i>< 0.03). <b>Conclusions</b>: 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.<br />