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Ca 2+ Sensitivity of Limb Muscle Fibers in Young and Older Adults
Author(s) -
Teigen Laura E.,
Sundberg Christopher W.,
Kelly Lauren J.,
Hunter Sandra K.,
Fitts Robert H.
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.04189
Subject(s) - medicine , myosin , ageing , endocrinology , sarcopenia , atrophy , chemistry , young adult , skeletal muscle , biochemistry
Age‐induced declines in skeletal muscle contractile function have been attributed to multiple cellular factors, including a loss of peak force (P O ), decreased Ca 2+ sensitivity, and reduced shortening velocity (V O ). However, changes in these cellular properties with aging remain unresolved, especially in older women, and the effect of submaximal Ca 2+ on contractile function is unknown. Thus, we compared contractile properties of muscle fibers from 19 young (24±3 years; 11 women) and 21 older adults (77±7 years; 7 women) under maximal and submaximal Ca 2+ and assessed the abundance of three proteins thought to influence Ca 2+ sensitivity. Fast fibers showed marked atrophy with aging in both men (young=8,599 μm 2 ; old=5,404 μm 2 ) and women (young=4,909 μm 2 ; old=3,174 μm 2 ) that corresponded with a decreased absolute P O in men (young=1.48 mN; old=0.92 mN) and women (young=0.85 mN; old=0.60 mN). There were no differences in fast fiber size‐specific P O , indicating the age‐related decline in force was explained by differences in fiber size. Except for fiber size and absolute P O , no age or sex differences were observed in Ca 2+ sensitivity, rate of force development (k tr ), or V O . Submaximal Ca 2+ depressed k tr and V O , but the effects were not altered by age in either sex. Contrary to rodent studies, regulatory light chain (RLC) and myosin binding protein‐C abundance and RLC phosphorylation were unaltered by age or sex. These data suggest the age‐induced decline in whole‐muscle contractile function is primarily due to the atrophy of fast fibers and that caution is warranted when extending results from rodent studies to humans. Support or Funding Information National Institute on Aging grant (R01AG048262) to Robert Fitts and Sandra Hunter and an American Heart Association postdoctoral fellowship (19POST34380411) to Christopher Sundberg