Ageing, but not yet senescent, rats exhibit reduced muscle quality and sarcoplasmic reticulum function

Aim: Reduced muscle force greater than expected from loss of muscle mass has been reported in ageing muscles. Impaired sarcoplasmic reticulum (SR) Ca2+ release has been implicated as a possible mechanism, and attributed to several factors, including loss of ryanodine receptor (RYR) expression and protein binding. The aim of this study was to evaluate muscle quality and SR Ca2+ release in ageing rats that were not so old that major atrophy had occurred. Methods: We collected in situ force data from the plantarflexor muscle group and muscle mass from the constituent muscles to determine muscle quality (force/mass) in adult (6-8 months) and ageing (24 months) rats (n = 8/group). We evaluated SR Ca2+ uptake and release, and determined expression of key proteins associated with Ca2+ release [RYR and FK506 binding protein (FKBP)] and uptake (SERCA, parvalbumin, calsequestrin). Results: Plantarflexor force and muscle quality were reduced with ageing (approx. 28 and 34%, respectively), but atrophy was limited, and significant only in the medial gastrocnemius (approx. 15%). The fast phase of SR Ca2+ release was reduced with ageing in both gastrocnemii, as was FKBP expression and FKBP-RYR binding, but RYR expression was not affected. Similar, but non-significant changes were present in the plantaris, but the soleus muscle generally showed no ageing-related changes. Conclusion: These data suggest a possible role for impaired SR Ca2+ release in ageing-related loss of muscle quality, although not through loss of RYR expression.