Meeting Abstract

P2.172  Saturday, Jan. 5  The scalenus and diaphragm muscles’ contributions to inspiration in the bottlenose dolphin (Tursiops truncatus) MCKINNEY, M.L.*; WALKER, R.A.; DEAROLF, J.L.; RICHMOND, J.P.; Hendrix College, Conway, AR; Univ. of North Florida, Jacksonville, FL mckinneyml@hendrix.edu

Dolphins have a unique ventilatory system that allows them to have an explosive intake of air during their brief rise to the surface. This extremely quick inhalation suggests that the muscles that drive this behavior are composed primarily of fast-twitch fibers. However, previous studies have shown that in bottlenose dolphins, the diaphragm, the main muscle of inspiration in terrestrial mammals, is composed primarily of slow twitch fibers, while the scalenus muscle is composed primarily of fast twitch fibers. These results suggest that the diaphragm and scalenus of bottlenose dolphins do not contract together to drive inspiration, and muscles that do not work together should be found to have different levels of oxidative enzyme activities. Samples of the diaphragm and scalenus muscles of eight bottlenose dolphins were taken and analyzed for their citrate synthase (CS) activity, which can be used as a measure of aerobic capacity. Extracts of the muscles were prepared, and their CS activities (μmol/min*g wet muscle mass) were measured with a Synergy HT microplate reader under the following conditions: 50 mM imidazole buffer (pH 7.5 @ 37°C), 0.25 mM DTNB, 0.4 mM acetyl-CoA, and 0.5 mM oxaloacetate. The scalenus muscle consistently had a higher CS activity (overall average: 15.07 +/- 0.91 μmol/min*g) than the diaphragm muscle (6.10 +/- 0.55 μmol/min*g) from the same bottlenose dolphin, which supports the hypothesis that the scalenus and diaphragm do not work together to power ventilation in bottlenose dolphins. Our results suggest that the diaphragm may not be the main muscle of inspiration in these cetaceans, because it does not have the fiber composition or aerobic capacity to drive this behavior.