AUTHOR=Mijares Alfredo , Allen Paul D. , Lopez Jose R. 

TITLE=Senescence Is Associated With Elevated Intracellular Resting [Ca2 +] in Mice Skeletal Muscle Fibers. An in vivo Study

JOURNAL=Frontiers in Physiology

VOLUME=Volume 11 - 2020

YEAR=2021

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2020.601189

DOI=10.3389/fphys.2020.601189

ISSN=1664-042X

ABSTRACT=Aging causes skeletal muscles to become atrophied, weak, and easily fatigued. Here we have tested the hypothesis that normal aging in skeletal muscle cells is associated with Ca2+ intracellular dyshomeostasis and oxidative stress. Intracellular Ca2+ concentration ([Ca2+]i), resting intracellular Na+ concentration ([Na+]i) and reactive oxygen species (ROS) production were measured in vivo (superficial gastrocnemius fibers) using double-barreled ion-selective microelectrodes, and in vitro (isolated single flexor digitorum brevis (FDB) fibers) using fluorescent ROS sensor CM-H2DCFDA in young (3 months of age), middle-aged (12 months of age), and aged (24 months of age) mice. We found an age-related increase in [Ca2+]i from 121±4 nM in young muscle cells to 255±36 nM in middle-aged and to 409±25 nM in aged cells. [Na+]i also showed an age-dependent elevation, increasing from 8±0.5 mM in young muscle fibers, to 12±1 mM in middle-aged and to 17±1 mM in aged muscle fibers. Using the ROS sensor CM-H2DCFDA we found significantly increased basal ROS production. We administered Flufenamic acid (FFA), a non-steroidal anti-inflammatory (NSAID), and a non-selective blocker of TRPCs, 12.5 mg/kg intraperitoneally daily for 4 weeks. FFA treatment reduced DCF fluorescence levels in middle-aged and aged muscle fibers and this decrease iwas associated with a significant reduction of [Ca2+]i and [Na+]i. In addition, FFA treatment also reduced the age associated increases in plasma interleukin 6 (IL-6) and tumor necrosis factor-alpha (TNF-α) concentrations which were elevated in 12 and 24-mo old mice compared to young mice and decreases age related muscle damaged as indicated by a reduction in serum creatine kinase (CK) activity. Our data provide the first direct demonstration that normal aging is associated with a significant elevation [Ca2+]i, [Na+]i, and intracellular ROS production in skeletal muscle fibers. Furthermore, the fact that FFA reduced the intracellular [Ca2+], [Na+], and ROS overload as well as the elevated IL6, TNF-α and CK levels, led us to suggest that its pharmacological effect may be related to its action as TRPC channel blocker and as an NSAID.