Effect of a 17 day spaceflight on contractile properties of human soleus muscle fibres

Abstract

Soleus biopsies were obtained from four male astronauts 45 days before and within 2 h after a 17 day spaceflight. For all astronauts, single chemically skinned post‐flight fibres expressing only type I myosin heavy chain (MHC) developed less average peak Ca2+ activated force (Po) during fixed‐end contractions (0.78 ± 0.02 vs. 0.99 ± 0.03 mN) and shortened at a greater mean velocity during unloaded contractions (Vo) (0.83 ± 0.02 vs. 0.64 ± 0.02 fibre lengths s−1) than pre‐flight type I fibres. The flight‐induced decline in absolute Po was attributed to reductions in fibre diameter and/or Po per fibre cross‐sectional area. Fibres from the astronaut who experienced the greatest relative loss of peak force also displayed a reduction in Ca2+ sensitivity. The elevated Vo of the post‐flight slow type I fibres could not be explained by alterations in myosin heavy or light chain composition. One alternative possibility is that the elevated Vo resulted from an increased myofilament lattice spacing. This hypothesis was supported by electron micrographic analysis demonstrating a reduction in thin filament density post‐flight. Post‐flight fibres shortened at 30 % higher velocities than pre‐flight fibres at external loads associated with peak power output. This increase in shortening velocity either reduced (2 astronauts) or prevented (2 astronauts) a post‐flight loss in fibre absolute peak power (μN (fibre length) s−1). The changes in soleus fibre diameter and function following spaceflight were similar to those observed after 17 days of bed rest. Although in‐flight exercise countermeasures probably reduced the effects of microgravity, the results support the idea that ground‐based bed rest can serve as a model of human spaceflight. In conclusion, 17 days of spaceflight decreased force and increased shortening velocity of single Ca2+‐activated muscle cells expressing type I MHC. The increase in shortening velocity greatly reduced the impact that impaired force production had on absolute peak power.

Human soleus single muscle fiber function with exercise or nutrition countermeasures during 60 days of bed rest

“…We did not isolate the cellular and whole muscle contributions of the gastrocnemius, which would have also played a role in overall calf muscle performance. This is emphasized from short-term (17 day) spaceflight showing the contractile properties of the gastrocnemius (60) are less affected than the soleus muscle (59). Changes in the cellular profile of the muscle were also modified and most likely contributed to whole muscle performance.…”

“…The V max data are obtained while the fiber is under tension while V o is measured when the fiber is completely unloaded. Typically, these two measures parallel each other in human studies (7,52,59). It should be considered, however, that the V max data more closely relates to how the fiber behaves in vivo (i.e., shortening while under tension).…”

Spaceflight results in increase of thick filament but not thin filament proteins in the paramyosin mutant of Caenorhabditis elegans

“…Weightlessness induces atrophy of skeletal muscle (Riley et al, 1987;Widrick et al, 1999) and cardiovascular deconditioning (Philpott et al, 1990;Antonutto and Prampero, 2003). Weightlessness also reduces functional capacity in limb skeletal muscle of animals including humans (Ilyina-Kakueva et al, 1976;Widrick et al, 1999;Fitts et al, 2000). In vertebrate skeletal muscle, the greatest changes are observed in the limb antigravity muscles, such as soleus (Riley et al, 1987;Widrick et al, 1999;Harrison et al, 2003).…”

“…Weightlessness also reduces functional capacity in limb skeletal muscle of animals including humans (Ilyina-Kakueva et al, 1976;Widrick et al, 1999;Fitts et al, 2000). In vertebrate skeletal muscle, the greatest changes are observed in the limb antigravity muscles, such as soleus (Riley et al, 1987;Widrick et al, 1999;Harrison et al, 2003). Major changes in these muscles alter the expression of muscle protein isoforms, mainly myosin heavy chains (MHCs).…”

“…One of the most affected is the neuromuscular system. Weightlessness induces atrophy of skeletal muscle (Riley et al, 1987;Widrick et al, 1999) and cardiovascular deconditioning (Philpott et al, 1990;Antonutto and Prampero, 2003). Weightlessness also reduces functional capacity in limb skeletal muscle of animals including humans (Ilyina-Kakueva et al, 1976;Widrick et al, 1999;Fitts et al, 2000).…”