title: Effects of support stimulation on human soleus fiber characteristics during exposure to "dry" immersion.
abstract: In this study the model of 7-day dry immersion (DI) was used. 17 male volunteers (23-29 years old) were divided in 2 groups: (i) 7-day DI without support (DI, n=9), (ii) 7-day DI using support stimulation (DIS, n=8). Support stimulator device exerted pressure of 0.2 +/- 0.15 kg/cm2 upon the plantar support zones simulating the walking pattern 6 times a day for 20 minutes of every hour: 10 minutes at a speed of 75 steps/min and 10 minutes at a speed of 120 steps/min. M. soleus biopsy was performed before and immediately after DI. The m. soleus fiber myosin heavy chain (MHC) profile, myofiber cross-sectional area (CSA) and total protein concentration were analyzed in frozen serial sections. In addition, NO-synthase 1 (NOS1) levels indicative of normal muscle cell signaling were analyzed by western blotting in 4 persons in each group. After dry immersion, percentage of muscle fibers containing type I MHC decreased by 6% (p<0.05) in group DI, but was not changed significantly in group DIS. Percentage of the type IIa fibers was significantly altered in none of the groups. Type I fiber CSA decreased by 24.4% (p<0.05) in group DI. No significant changes of type I fiber CSA were found in group DIS. CSA of the type IIa fibers significantly altered in none of the groups. The total protein concentration was found increased by 17.6% in group DI and by 21% in group DIS. The increased total protein content in group DI suggests a diminution of fiber CSA attributed to the loss of non-protein component of fibers. NOS1 decreased by 35.6% in group DI and increased by 58.1% in group DIS. We conclude that 7 days in dry immersion lead to reduction in the type I muscle fiber percentage, loss of the non-protein component and decline in NOS1. These changes were clearly prevented by the support stimulation protocol applied during the DI period.
authors.affiliation: State Research Center of Russian Federation Institute for Biomedical Problems RAS, Moscow, Russia.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Moukhina
authors.forename: Boris
authors.initials: B
authors.lastname: Shenkman
authors.forename: Dieter
authors.initials: D
authors.lastname: Blottner
authors.forename: Tatiana
authors.initials: T
authors.lastname: Nemirovskaya
authors.forename: Yulia
authors.initials: Y
authors.lastname: Lemesheva
authors.forename: Britta
authors.initials: B
authors.lastname: Püttmann
authors.forename: Inessa
authors.initials: I
authors.lastname: Kozlovskaya
mesh_terms: D000328:Adult; D005528:Foot; D006801:Humans; D007101:Immersion; D008297:Male; D018656:Muscle Fibers, Fast-Twitch; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D011312:Pressure; D016138:Walking / Q000502:physiology; D018474:Weightlessness Simulation
chemical_list: D009124:Muscle Proteins; D019001:Nitric Oxide Synthase; D018995:Myosin Heavy Chains