De La Cruz, Lourdes

Desplanches, Dominique

Fitts, Robert

Romatowski, Janell

Widrick, Jeffrey J.

English

epublications@Marquette

Marquette University e-Publications@Marquette Biological Sciences Faculty Research and Publications Biological Sciences, Department of 2000 Effect of Spaceflight on the Maximal Shortening Velocity, Morphology, and Enzyme Profile of Fast- and Slow-Twitch Skeletal Muscle Fibers in Rhesus Monkeys Robert Fitts Janell Romatowski Lourdes De La Cruz Jeffrey J. Widrick Dominique Desplanches Follow this and additional works at: https://epublications.marquette.edu/bio_fac  Part of the Biology Commons EFFECT OF SPACEFLIGHT ON THE MAXIMAL SHORTENING VELOCITY, MORPHOLOGY, AND ENZYME PROFILE OF FAST- AND SLOW-TWITCH SKELETAL MUSCLE FIBERS IN RHESUS MONKEYS Robert H. Fitts 1, Janell G. Romatowski1, Lourdes De La Cruz 1, Jeffrey J. Widrick1, and Dominigue Desplanches2 1Departmenf of Biology, Marquette University, Milwaukee, WI, USA 2Centre National de la Recherche Scientifique, Laboratoire de Physiologie, Lyon, France INTRODUCTION Weightlessness has been shovm to cause limb muscle wasting and a reduced peak force and power in the antigravity soleus muscle [l, 2). Despite a reduced peak power, Caiozzo ct al. [2] observed an increased maximal shortening velocity in the rat soleus muscle following a 14-day space flight. The major purpose of the present investigation was to determine if weightlessness induced an elevated velocity in the antigravity slow type I fibers of the rhesus monkey (Macaca mu/atta), as ,,veil as to estab~ Hsh a cellular mechanism for the effect. Spaceflight or models of weightlessness have been shown to increase glucose uptake [6], elevate muscle glycogen content, and increase fatigability of the soleus muscle {2]. The latter appears to be in part caused bv a reduced abilitv of the slow oxidative fibers to ~xidize fats {1]. /\ ;econd goal of this study was to establish the extent to which weightlessness altered the substrate profile and glycolytic and oxida­tive enzyme capacity of individual slow- and fast­twitch fibers. METHODS The animal selection and biopsy procedures are described in the companion abstract [Fitts et al., p. 53). Single fibers were isolated and the fo\lowing pararne­ten; were measured: 1) peak force {P ); 0 2) maximal unloaded shortening velocity (V 0); and 3) peak rate of tension redevelopment, ktr· Following each exper­iment, the fiber was solubilized in SOS and the pro­file of the myosin heavy and light chain isozymes was determined. A 1 mm cross-section v-:as cut from the soleus biopsy and fixed in 6.25% glutaraldehyde for determination of mitochondria and myofibril con­tent. Single fiber biochemical assays were conducted on freeze-dried fibers by enzymatic cycling. RESULTS Maximal unloaded shortening velocity (V), and peak rate of tension redevelopment (k1r) The maximal shortening velocity (V ) 0 of the slow type I soleus fiber decreased with gro.-vth (0.94 ± 0.04 vs 0.85 ± 0.03 FL/s), but it showed a slight increase (significant at p< 0.1) compared to the post-vivarium group following both flight (0.96 ± 0.04 Fl/s) and the R+17 simulation (1.04 ± 0.04 FL/s). The increased velocity of the slow type I fiber was not caused by the expression of fast type proteins. This population of fibers contained no fast myosin heavy chain, and although the myosin light chain (MLC) 2s/tota1 MLC ratio was increased, there was no change in the MLC3 /MLC2 ratio. Growth decreased VO in the type I (0.84 ± 0.03 vs 0.55 ± 0.03 FL/s) andH (5.82 ± 0.43 vs 4.37 ± 0.36 FL/ s) gastrocnemius fibers, but in contrast to the soleus, flight had no effect on this variable in the gastrocnemius. In the type I soleus fiber, ktr sig­nificantly declined in the vivarium group (2.48 ± .05 vs 2.07 ± .05 s-1), but was not altered in the R+I7 or flight groups. Similar results were observed for the type I gastrocnemius fibers. Morphology We hypothesized that spaceflight might induce a selective loss of myofibrillar protein. However, the myofibrilbr volume density (%) of the soleus fibers was unchanged by flight. The myofibril1ar density of the 2 flight animals preflii=;ht was 71.8% and 69.8% compared to 74.0% and 69]% postflight. The vivari­um control and R+l7 groups showed myofibrillar densities that were not significantly different from the flight animals. Single fiber enzyme and substrates Flight had no significant effect on any of the gly­colytic (glycogen synthase [GS], phosphorylase [PPj, hcxokinase lHKJ, phosphofrm::tok.inase [PFK]; lactate dehydrogenase (LOH]) or oxidative (~-hydroxyacyl­CoA dehydrogeriase [!3OAC] and citrate synthase Copyrlght ([) 2000 Galileo Foundation S-37 [CSJ) enzymes assayed in either the slow- or fast­twitch fiber types. Additionally, the acetyl-CoA regu­lating enzyme camitine acetyltransferase (CAT) was unaltered by flight. Further evidence that mitochon­dria are resistant to alteration with microgravity was the finding that mitochondrial volume density showed no significant change in any of the three groups. The substrates-glycogen, ATP, PCr- and lactates were also unaltered by flight. CONCLUSIONS The Flight and the R+17 groups showed a small increase in the type I fiber V0 compared to the 2nd vivarium controls (p<0.l). This increase could not be explained by an altered myosin heavy or light chain pattern. We hypothesized that the change might be caused by an increased myofilament lattice spacing. Although the myofibrillar volume density measure­ments do not support this idea, the possibility exists that the sensitivity of the morphome trk analysis was insufficient to detect small but functionally signifi­cant increase in the myofilament lattice spacing. This change would expla.in the increased VO and the reduced peak force (kN/m2) of the slow type I fiber. Spaceflight has been shown to reduce fatty acid oxi­dation in rat soleus muscle [1]. The present results demonstrate that the spaceflight-induced inhibiti.on of fat oxidation cannot be explained by a reduced CAT or ~OAC activity. Unlike bed rest, spaceflight did not cause glycogen loading. The failure of space­flight to increase cell glycogen in the slow type I fiber may have resulted from insufficient caloric or carbo­hydrate intake inflight. REFERENCES 1. Baldwin, K.M., RE. Herrick, and S.A. McCue. Substrate oxida tion capacity in rodent skeletal muscle: effects of exposure to zero gravity. J. Appl. Physiol. 75: 2466-2470, 1993. 2. Caiozzo, V.J., M.J. Baker, R.E. Herrick, M. Tao, and KM. Baldwin. Effect of spaceflight on skeletal muscle: mechanical properties and myosin isoform content of a slow muscle. J. Appl. Physiol. 76: 1764-1773, 1994. 3. Fitts, R.H., C.J. Brimmer, A. Heywood-Cooksey, and R.J. Timmerman. Single muscle fiber enzyme shifts with hindlimb suspension and immobilization. Am. J. Physiol. 2.56: C1082-C1091, 1989. 4. Hoppeler, H., H. Howald, KE. Conley, S.L Lindsted, H. Claassen, P. Vock, and E.R. Weibel. Endurance train­ing in h umans: aerobic capacity and structure of skele­tal muscle. J. Appl. Physiol. 59: 320-327, 1985. 5. Lowry, O.H. and J.V. Passonneau. A Flexible System of Enzymatic Analysis. New York, Academic Pl'ess, 1972. 6. Tischler, M.E., E.J. Henriksen, KA. Munoz, C.S. Stump, C.R. Woodman, and C.R. Kirby. Spaceflight on STS-48 and earth-based unweighting produce similar effects on skeletal muscle of young rats. J. Appl. Physiol. 74: 2161-2165, 1993. 7. Widrick, J.J., J.G. Romatowsk i, J.L W. Bain, S.W, Trappe, T.A. Trappe, J.L.Thompson, D.L. Costill, D.A. Riley, and R.H. Fitts. Effect of 17 days of bed rest on peak isometric force and unloaded shortening velocity of human soleus fibers. AnL / . Physiol. 273: Cl690-C1699, 1997. Journal of Gravitational Physiology • Vol 7(1) • 2000 S--38 

Effect of Spaceflight on the Maximal Shortening Velocity, Morphology, and Enzyme Profile of Fast- and Slow-Twitch Skeletal Muscle Fibers in Rhesus Monkeys

https://epublications.marquette.edu/cgi/viewcontent.cgi?article=1803&amp;context=bio_fac

Effect of Spaceflight on the Maximal Shortening Velocity, Morphology, and Enzyme Profile of Fast- and Slow-Twitch Skeletal Muscle Fibers in Rhesus Monkeys

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