Ca²⁺ Dependency of Limb Muscle Fiber Contractile Mechanics in Young and Older Adults

Authors

Laura E. Teigen, Marquette University
Christopher W. Sundberg, Marquette UniversityFollow
Lauren J. Kelly, Marquette University
Sandra Hunter, Marquette UniversityFollow
Robert Fitts, Marquette UniversityFollow

Document Type

Article

Language

eng

Publication Date

6-2020

Publisher

American Physiological Society

Source Publication

American Journal of Physiology: Cell Physiology

Source ISSN

0002-9513

Original Item ID

DOI: 10.1152/ajpcell.00575.2019

Abstract

Age-induced declines in skeletal muscle contractile function have been attributed to multiple cellular factors, including lower peak force (P_o), decreased Ca²⁺ 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 Ca²⁺ on contractile function is unknown. Thus, we compared contractile properties of muscle fibers from 19 young (24 ± 3 yr; 8 women) and 21 older adults (77 ± 7 yr; 7 women) under maximal and submaximal Ca²⁺ and assessed the abundance of three proteins thought to influence Ca²⁺ sensitivity. Fast fiber cross-sectional area was ~44% larger in young (6,479 ± 2,487 µm²) compared with older adults (4,503 ± 2,071 µm², P < 0.001), which corresponded with a greater absolute P_o (young = 1.12 ± 0.43 mN; old = 0.79 ± 0.33 mN, P < 0.001). 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 fast fiber size and absolute P_o, no age or sex differences were observed in Ca²⁺ sensitivity, rate of force development (k_tr), or V_o in either slow or fast fibers. Submaximal Ca²⁺ 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-associated reductions in contractile function are primarily due to the atrophy of fast fibers and that caution is warranted when extending results from rodent studies to humans.

Comments

Accepted version. American Journal of Physiology: Cell Physiology, Vol. 318, No. 6 (June 2020): C1238-C1251. DOI. © 2020 American Physiological Society. Used with permission.

Recommended Citation

Teigen, Laura E.; Sundberg, Christopher W.; Kelly, Lauren J.; Hunter, Sandra; and Fitts, Robert, "Ca²⁺ Dependency of Limb Muscle Fiber Contractile Mechanics in Young and Older Adults" (2020). Exercise Science Faculty Research and Publications. 189.
https://epublications.marquette.edu/exsci_fac/189