Faculty Collaboration Database

Ca²⁺ dependency of limb muscle fiber contractile mechanics in young and older adults. Am J Physiol Cell Physiol 2020 Jun 01;318(6):C1238-C1251

Date

04/30/2020

Pubmed ID

32348175

Pubmed Central ID

PMC7311743

DOI

10.1152/ajpcell.00575.2019

Scopus ID

2-s2.0-85085961827 (requires institutional sign-in at Scopus site)   13 Citations

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.

Author List

Teigen LE, Sundberg CW, Kelly LJ, Hunter SK, Fitts RH

Authors

Robert Fitts PhD Professor in the Biological Sciences department at Marquette University
Chrisopher Sundberg in the CTSI department at Medical College of Wisconsin - CTSI

MESH terms used to index this publication - Major topics in bold

Adult
Age Factors
Aged
Aged, 80 and over
Aging
Calcium
Calcium Signaling
Carrier Proteins
Female
Humans
Male
Muscle Contraction
Muscle Fibers, Skeletal
Muscle Strength
Myosin Heavy Chains
Myosin Light Chains
Quadriceps Muscle
Sex Factors
Time Factors
Young Adult