Meeting Abstract

P2.173  Saturday, Jan. 5  Investigating the presence of a venous sphincter in the bottlenose dolphin (Tursiops truncatus) diaphragm UNSER, A.J.*; DEAROLF, J.L; RICHMOND, J.P.; Hendrix College, Conway, AR; Univ. of North Florida, Jacksonville, FL unseraj@hendrix.edu

Adaptations of deep diving marine mammals include a sphincter around the vena cava where it passes through the diaphragm, which prevents pressurized blood from rushing back to the heart. Sphincters are composed of slow-twitch muscle fibers, which contain more mitochondria than their counterparts, fast-twitch fibers. A standard marker for the presence of mitochondria is the enzyme citrate synthase (CS). Thus, if bottlenose dolphins have a caval sphincter, muscle tissue around the vena cava should have higher CS activity than the costal region of the diaphragm. To test this hypothesis, CS kinetic assays were performed on muscle samples from three regions of ten bottlenose dolphin diaphragms: costal, dorsal caval (region directly dorsal to the caval foramen), and ventral caval. The CS activity of each sample was determined in 50 mM imidazole buffer (pH 7.5 at 37°C), 0.25 mM DTNB, 0. mM acetyl-CoA, and 0.5 mM oxaloacetate using a microplate reader. The activities were calculated from the rate of change of the assay absorbance (412 nm) at the maximal linear slope (Vmax). After comparative analyses, it was concluded that there was a difference in CS enzyme activity between the costal and caval regions of the diaphragm. However, on average, the costal region showed higher CS activity at 6.30 ± 0.40 μmol/min∙g than the dorsal and ventral caval regions, which averaged 4.31 ± 0.43 and 5.40 ± 0.63 μmol/min∙g, respectively. These results do not support our hypothesis that a sphincter exists in the caval region of the bottlenose dolphin diaphragm. These findings suggest that bottlenose dolphins rely on other adaptations for diving to depth, and since these cetaceans are typically shallow divers, they may not require a caval sphincter.