Meeting Abstract

63.2  Sunday, Jan. 5 13:45  Significance of Muscle Fiber Type in Biopsied Elephant Seals MOORE, C.D*; FAHLMAN, A.; MOORE, M.J.; WILLOUGHBY, D.; ROBBINS, K.; TRUMBLE, S.J.; Baylor University; Texas A&M University; Woods Hole Oceanographic Institution; Baylor University; Baylor University; Baylor University colby_moore@baylor.edu

Northern elephant seals (Mirounga angustirostris) are known to be elite deep divers, often thought to exceed the aerobic dive limit (ADL), a threshold utilized to measure the point at which depletion of oxygen and thus shift to anaerobic pathways of metabolism occur during a dive. It was found that most pinniped dives are within this ADL, and thus aerobic. Diving physiology often thought to reinforce the ADL are lung compression, bradycardia and peripheral vasoconstriction, among others. There are little data pertaining to fiber type ratios of diving mammal locomotory muscles. Research suggests an absence of Type IIb muscle fibers in pinniped locomotory musculature. In this study, Northern elephant seals were biopsied in the wild and succinate dehydrogenase (SDH) based fiber typing revealed the predominance of one fiber type in the longissimus dorsi (LD) muscle of elephant seals: Type I. Type IIb muscle fibers appeared to be absent altogether. Previously, any lack of Type II fibers has been attributed to the increased reliance on aerobic-based metabolism during dives, lower overall metabolic rate, and maintenance of low energy locomotion. Here, we concurred with previous findings, suggestive of our finding of large fiber diameters and elevated myoglobin concentrations, but further suggested the lack of Type IIb fibers, specifically, may provide a cautionary explanation for the apparent avoidance for ischemia reperfusion injury in vasoconstricted peripheral skeletal muscle during a dive.