RAUER, E.M.; FELDMAN, R.A.; JACKSON, D.C.; Brown University: Avenues of Aquatic Oxygen Uptake in Painted Turtles (Chrysemys picta belli) at 10�C

Painted turtles can survive long periods submerged in water without access to air, which they must do every winter in northern latitudes. They can take up oxygen from water, but how they do this is uncertain. There are three proposed methods of O₂ uptake: cloacal pumping, buccal pumping, and diffusion through the skin. The relative contribution of these three avenues of O₂ uptake was examined by selectively eliminating one or more of these avenues of gas exchange. All turtles were acclimated to 10�C, submerged in sealed tanks, and the PO₂ of the water recorded for 3-4 hours. No significant differences were found between the rate of O₂ consumption in unmanipulated turtles and turtles with their head, cloaca, or both covered. Turtles with their skin covered had significantly lower rates of O₂ consumption. Similar results were found when various methods for covering the skin were tested. The final experiments used a skeletal muscle paralytic, rocuronium, to prevent cloacal and buccal pumping either with or without prior equilibration with nitrogen to maximize the O₂ gradient. Without pre-exposure to nitrogen, rocuronium had no effect on O₂ uptake. With nitrogen exposure, however, unparalyzed turtles had significantly higher rates of O₂ consumption than those that received rocuronium. We suggest two possible interpretations of these most recent findings: 1) that cloacal and buccal pumping is contributing to aquatic oxygen uptake or 2) a boundary layer forms around paralyzed turtles decreasing the rate of diffusion through the skin. Overall the results suggest that the skin is the major avenue for O₂ uptake, but a contribution of buccal and cloacal pumping cannot be excluded. Supported by NSF grant IBN 01-10322.