POWERS, D.R.*; ANDREWJESKI, P.M.; GRAMENZ, P.W.; KIMBERLY, D.J.: Cutaneous water abosorption by Rough-skinned Newts (Taricha granulosa) in open terrain vs. water-soaked environments.

We measured cutaneous water uptake rate in Rough-skinned Newts (Taricha granulosa) using an open terrestrial (ventral surface only) and submergence (whole body) model to evaluate their ability to regulate water balance in open terrain vs. water-soaked environments. These are meaningful measurements for this species because they have both an aquatic and terrestrial phase during their annual cycle, and the osmoregulatory challenges of these two periods are dramatically different. We hypothesized that net water flux rate (absorption rate – evaporation) would be higher in the submergence model based on two factors. First, this species is aquatic for much of the year and is likely adapted primarily to this environment. Second, using immunohistochemistry we have shown that the outer skin cells of both the dorsal and ventral surfaces of the newt contain high densities of aquaporin (AQP) water channels. This indicates that these surfaces are probably actively involved in water absorption. Surprisingly, our measurements show that net water flux rate in the open terrestrial model is slightly higher than in the submergence model. While the reasons for this result have yet to be determined, it is possible that ventral skin permeability is increased at appropriate times to maximize absorption rate. One way to control skin permeability to water is to regulate the number of active AQP water channels. Hormones such as ADH, AVT, and AII will likely be major players in the regulation of skin permeability regardless of the role of AQP. Previous studies have shown that some AQP water channels are responsive ADH. We are currently working to sequence the AQP in newt skin so it can be compared to those that have shown ADH sensitivity.