Age-related changes affect rat rotator cuff muscle function.

Background: The influence of age on rotator cuff function and muscle structure remains poorly understood. We hypothesize that normal aging influences rotator cuff function, muscle structure, and regulatory protein expression in an established rat model of aging.

Methods: Seventeen rats were obtained from the National Institute on Aging.

Role of sustained overexpression of central nervous system IGF-I in the age-dependent decline of mouse excitation-contraction coupling.

We investigated the effects of exclusive and sustained transgenic overexpression of insulin-like growth factor (IGF)-I in the central nervous system (CNS) on the age-dependent decline in muscle strength, excitation-contraction coupling, muscle innervation and neuromuscular junction postterminal architecture. We found that (1) transgenic IGF-I overexpression in the CNS does not modify the decline in extensor digitorum longus (EDL) and soleus muscle weight with aging and (2) strength significantly decreases in transgenic (Tg) compared to wild-type mice. The latter finding is consistent with (3) the decreased absolute and specific force measured in the EDL muscle in vitro and (4) the decreased charge movement and peak intracellular Ca(2+) mobilization in individual muscle fibers from old IGF-I Tg mice compared to young wild-type mice, which also is associated with (5) decreased dihydropyridine receptor alpha(1)-subunit expression in old compared to young IGF-I Tg mice.