Soleus muscle stability in wild hibernating black bears

D. A. Riley, J. M. Van Dyke, V. Vogel, B. D. Curry, J. L. W. Bain, R. Schuett, D. L. Costill, T. Trappe, K. Minchev, S. Trappe
2018 American Journal of Physiology. Regulatory Integrative and Comparative Physiology  
Based on studies of fast skeletal muscles, hibernating black and brown bears resist skeletal muscle atrophy during months of reduced physical activity and not feeding. The present study examined atrophy sparing in the slow soleus muscle, known to be highly prone to disuse atrophy in humans and other mammals. We demonstrated histochemically that the black bear soleus is rich in slow fibers, averaging 84.0 Ϯ 6.6%. The percentages of slow fibers in fall (87.3 Ϯ 4.9%) and during hibernation (87.1 Ϯ
more » ... hibernation (87.1 Ϯ 5.6%) did not differ (P ϭ 0.3152) from summer. The average fiber cross-sectional area to body mass ratio (48.6 Ϯ 11.7 m 2 /kg) in winter hibernating bears was not significantly different from that of summer (54.1 Ϯ 11.8 m 2 /kg, P ϭ 0.4186) and fall (47.0 Ϯ 9.7 m 2 /kg, P ϭ 0.9410) animals. The percentage of single hybrid fibers containing both slow and fast myosin heavy chains, detected biochemically, increased from 2.6 Ϯ 3.8% in summer to 24.4 Ϯ 24.4% (P ϭ 0.0244) during hibernation. The shortening velocities of individual hybrid fibers remained unchanged from that of pure slow and fast fibers, indicating low content of the minority myosins. Slow and fast fibers in winter bears exhibited elevated specific tension (kN/m 2 ; 22%, P ϭ 0.0161 and 11%, P ϭ 0.0404, respectively) and maintained normalized power. The relative stability of fiber type percentage and size, fiber size-to-body mass ratio, myosin heavy chain isoform content, shortening velocity, power output, and elevated specific tension during hibernation validates the ability of the black bear to preserve the biochemical and performance characteristics of the soleus muscle during prolonged hibernation. atrophy; biopsy; body mass; denning; hibernation; muscle fiber; myosin † Deceased 8 February 2018. • www.ajpregu.org their licensed hunters were essential for obtaining specimens and weights from fall bears killed over six hunting seasons. For a variety of contributions to the field research, we thank a number of individuals who deserve credit, including
doi:10.1152/ajpregu.00060.2018 pmid:29641232 fatcat:viuuftqzmffdxcpzyn5ptn3kgy