Na,K-ATPase α- and β-isoform expression in developing skeletal muscles: α₂ correlates with t-tubule formation

Abstract.

This study examined the developmental expression of Na,K-ATPase α- and β-subunit isoforms in different skeletal muscles of the mouse, and the relationship of Na,K-ATPase α₂ isoform expression to the developing transverse tubules (t-tubules). We measured Na,K-ATPase and dihydropyridine receptor (DHPR) mRNA and protein in the diaphragm and hindlimb muscles from embryonic day 18.5 (E18.5) to 6 weeks postnatal, using DHPR expression to mark the timing of t-tubule formation. The Na,K-ATPase subunits showed developmental age-dependent and muscle-specific expression that was controlled by both transcriptional and post-transcriptional mechanisms. The α₁ isoform is expressed at more constant levels in both diaphragm and hindlimb muscles, while the α₂ and β₂ isoforms increase postnatally and show greater muscle variation. β₁ is the sole expressed β-subunit in the diaphragm throughout development, and in the hindlimb muscles at birth. The Na,K-ATPase α₂ subunit is expressed during development when the t-tubules form. These results suggest that the α₂ isoform may serve, in part, a physiological role in the muscle t-tubules.