Oligomeric Status of the Dihydropyridine Receptor in Aged Skeletal Muscle

A prominent feature of aging is represented by a decrease in muscle mass and strength. Abnormalities in Ca²⁺-regulatory membrane complexes are involved in many muscular disorders. In analogy, we determined potential age-related changes in a key component of excitation-contraction coupling, the dihydropyridine receptor. Immunoblotting of the microsomal fraction from aged rabbit muscle revealed a drastic decline in the voltage-sensing α₁-subunit of this transverse-tubular receptor, but only marginally altered expression of its auxiliary α₂-subunit and the Na⁺/K⁺-ATPase. A shift to slower fibre type characteristics was indicated by an age-related increase in the slow calsequestrin isoform. Chemical crosslinking analysis showed that the triad receptor complex has a comparable tendency of protein–protein interactions in young and aged muscles. Hence, a reduced expression and not modified oligomerization of the principal dihydropyridine receptor subunit might be involved in triggering impaired triadic signal transduction and abnormal Ca²⁺-homeostasis resulting in a progressive functional decline of skeletal muscles.