A: RNA concentration relative to muscle wet weight ( n = 9 participants). Markers of ribosomal biogenesis and ribosome content. AC, aerobically conditioned CTL, control MHCII, myosin heavy chain II SC, satellite cells WGA, wheat germ agglutinin. Two-way repeated measures of variance, *significant effect of time, †significant effect of condition (AC > CTL). ) and AC (■) legs, where each color represents a different participant and is overlayed on means (middle, horizontal line) ± SD (vertical line).All values are individual data points for the CTL ( Type-II-specific quiescent ( n = 11 J), activated ( n = 12 K), and differentiating ( n = 11 L) SC Pre, 24, and 48 h following eccentric contractions. Type-I-specific quiescent (PAX7 +/MYOD − n = 12 participants G), activated (PAX7 +/MYOD + n = 11 H), and differentiating (PAX7 −/MYOD + n = 12 I) SC. The red arrows indicate PAX7 +/MYOD − cells, yellow arrows indicate PAX7 +/MYOD + cells, and green arrows indicate PAX7 −/MYOD + cells, and the scale bar is 100 μm. Representative images of immunofluorescent stains for PAX7, MYOD, MHCII and WGA, and DAPI overlayed ( A), MYOD ( B), MYOD and DAPI ( C), PAX7, MYOD, and DAPI ( D), PAX7 ( E), and PAX7 and DAPI ( F). AC, aerobically conditioned CTL, control MHCI, myosin heavy chain I SC, satellite cells. Two-way repeated measures of variance, *significant effect of time, †significant effect of condition (AC > CTL), ‡significant time × condition interaction, Φsignificant difference between means (Tukey’s honest significant difference test, P < 0.05). Myogenic genes Pax7 ( H n = 10), MyoD1 ( I n = 10), and Myf5 ( J n = 10) mRNA expression Pre, 24, and 48 h following eccentric contractions. SC per 100 fibers for SC located to type-I ( E), type-II ( F), and mixed-fibers ( G n = 14 participants). The white arrows indicate PAX7 +/DAPI + cells and the scale bar is 100 μm. Representative images of immunofluorescent stains for MHCI, Laminin, MHCII and PAX7 overlayed ( B), PAX7 ( C), and PAX7 and DAPI ( D). Ribosomes satellite cells skeletal muscle translation translational capacity. We discovered that aerobic conditioning increased type-I SC abundance and the acute increase in ribosome content following eccentric contractions. Only the AC leg increased (Pre-24h) 45S pre-rRNA, 5.8S ITS, and 28S ITS following eccentric contractions. AC had greater RNA concentration and mRNA expression of Ubf and Tif-1a compared with CTL. A main effect of condition for Pax7 and MyoD1 mRNA expression was observed where expression was greater in the AC leg compared with the CTL. SC content (PAX7 + cells/100 fibers) in type I and mixed fibers showed a main effect of condition, where values were greater in the AC leg compared with the CTL. Pre-eccentric contractions, 45S pre-rRNA and 5.8S internal transcribed spacer (ITS) expression were lower in the AC leg compared with the CTL leg. Muscle biopsies were taken from the vastus lateralis of the aerobically conditioned (AC) and the control (CTL) legs before (Pre), 24 (24 h), and 48 (48 h) h post-contractions. Fourteen young men and women underwent 6 wk of single-legged aerobic conditioning followed by an acute bout of 300 eccentric contractions on each leg. However, the acute SC and ribosome exercise response with prior aerobic conditioning is unknown. Both are thought to increase acutely after resistance exercise and chronically with resistance training. Satellite cells (SCs) and ribosomes are key determinants of the skeletal muscle adaptive response.
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