BRICKELL, E.C.*; MCLELLAN, W.A.; PABST, D.A.; DEAROLF, J.L.; Hendrix College, Conway, AR; University of North Carolina at Wilmington; University of North Carolina at Wilmington; Hendrix College, Conway, AR: Metabolic characteristics of the harbor porpoise (Phocoena phocoena) scalenus muscle

Like most cetaceans, harbor porpoises exhale and inhale very quickly in order to minimize the time spent at the surface. Consequently, we expect their inspiratory ventilatory muscles to be composed of primarily fast-twitch glycolytic (FG) fibers, because although harbor porpoises breathe quickly, they then hold their breath for twenty to forty seconds, which is enough time for the muscle to recuperate from contractions without requiring oxidative respiration. This study therefore investigated the scalenus muscle (a primary inspiratory muscle) in the harbor porpoise, focusing on the levels of oxidative (NADH and SDH) and glycolytic (GPD) enzymes, the concentration of myoglobin ([Mb]), and fiber-type profile as demonstrated by the myosin ATPase assay. Histochemical measures of ATPase activity suggest that the scalenus muscle (scalene) is composed of predominantly fast-twitch fibers [63.6 +/- 3.7% (1 S.D.)]. However, a qualitative assessment of the levels of oxidative enzymes in the scalenes suggests that the muscle fibers are primarily oxidative. This conclusion is supported by the [Mb] found in the muscles (2.19 +/- 0.34 g Mb/100 g of wet muscle), a level that is comparable to the [Mb] found in the diaphragms of other cetacean species, muscles that are known to be largely oxidative. These findings suggest that the fast-twitch fibers in the harbor porpoise scalene are oxidative-glycolytic (FOG), rather than only glycolytic. Therefore, because the recovery time for this muscle should be long enough to rely exclusively on glycolytic energy production, the harbor porpoise scalenus muscle may have additional functions that require the more efficient energy production provided by oxidative respiration.