Functional properties of slow and fast gastrocnemius muscle fibers after a 17-day spaceflight

• Published in: Journal of applied physiology (1985) Vol. 90; no. 6; pp. 2203 - 2211
• Main Authors: Widrick, J. J, Romatowski, J. G, Norenberg, K. M, Knuth, S. T, Bain, J. L. W, Riley, D. A, Trappe, S. W, Trappe, T. A, Costill, D. L, Fitts, R. H
• Format: Journal Article
• Language: English
• Published: Legacy CDMS Am Physiological Soc 01.06.2001; American Physiological Society
• Subjects: Applied physiology; Astronauts; Atrophy; Biological and medical sciences; Calcium - pharmacology; Electrophoresis, Polyacrylamide Gel; Ergonomics. Work place. Occupational physiology; Gravity; Human physiology applied to population studies and life conditions. Human ecophysiology; Humans; Life Sciences (General); Medical sciences; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle Fibers, Fast-Twitch - physiology; Muscle Fibers, Fast-Twitch - ultrastructure; Muscle Fibers, Slow-Twitch - physiology; Muscle Fibers, Slow-Twitch - ultrastructure; Muscle, Skeletal - cytology; Muscle, Skeletal - physiology; Muscle, Skeletal - ultrastructure; Muscular system; Myofibrils - physiology; Space biology; Space Flight; Space life sciences; Clinical Trial; Non-Nasa Center; Sts-78 Shuttle Project; Nasa Discipline Musculoskeletal; Manned; Short Duration; Nasa Experiment Number 8913020 1/2; Flight Experiment; Human; Crew; Astronaut; Contractility; Muscular fiber type I; Contractile protein; Environmental factor; Weightlessness; Space flight; Striated muscle; Muscular fiber type II; Atrophy; Myosin; Gastrocnemius muscle; Microgravity; NASA Experiment Number 8913020 1/2; NASA Discipline Musculoskeletal; Non-NASA Center
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.2001.90.6.2203

1  Department of Biology, Marquette University, Milwaukee 53201; 2  Department of Cellular Biology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin 53226; and 3  Human Performance Laboratory, Ball State University, Muncie, Indiana 47306 The purpose of this investigation was to study the effects of a 17-day spaceflight on the contractile properties of individual fast- and slow-twitch fibers isolated from biopsies of the fast-twitch gastrocnemius muscle of four male astronauts. Single chemically skinned fibers were studied during maximal Ca 2+ -activated contractions with fiber myosin heavy chain (MHC) isoform expression subsequently determined by SDS gel electrophoresis. Spaceflight had no significant effect on the mean diameter or specific force of single fibers expressing type I, IIa, or IIa/IIx MHC, although a small reduction in average absolute force (P o ) was observed for the type I fibers (0.68 ± 0.02 vs. 0.64 ± 0.02   mN, P  < 0.05). Subject-by-flight interactions indicated significant intersubject variation in response to the flight, as postflight fiber diameter and P o where significantly reduced for the type I and IIa fibers obtained from one astronaut and for the type IIa fibers from another astronaut. Average unloaded shortening velocity [ V o , in fiber lengths (FL)/s] was greater after the flight for both type I (0.60 ± 0.03 vs. 0.76 ± 0.02 FL/s) and IIa fibers (2.33 ± 0.25 vs. 3.10 ± 0.16 FL/s). Postflight peak power of the type I and IIa fibers was significantly reduced only for the astronaut experiencing the greatest fiber atrophy and loss of P o . These results demonstrate that 1 ) slow and fast gastrocnemius fibers show little atrophy and loss of P o but increased V o after a typical 17-day spaceflight, 2 ) there is, however, considerable intersubject variation in these responses, possibly due to intersubject differences in in-flight physical activity, and 3 ) in these four astronauts, fiber atrophy and reductions in P o were less for slow and fast fibers obtained from the phasic fast-twitch gastrocnemius muscle compared with slow and fast fibers obtained from the slow antigravity soleus [J. J. Widrick, S. K. Knuth, K. M. Norenberg, J. G. Romatowski, J. L. W. Bain, D. A. Riley, M. Karhanek, S. W. Trappe, T. A. Trappe, D. L. Costill, and R. H. Fitts. J Physiol (Lond) 516: 915-930, 1999]. muscle atrophy; muscle disuse; microgravity; nonweight bearing; myosin heavy chain