Meeting Abstract

P1.50  Wednesday, Jan. 4  Long term exposure to high environmental ammonia (HEA) impairs net ammonia secretion over the skin of the African Clawed Frog, Xenopus laevis CRUZ, M.J.; SOURIAL, M.M.; WEIHRAUCH, D.*; University of Manitoba; University of Manitoba; University of Manitoba weihrauc@cc.umanitoba.ca

Ammonia excretion rates of the fully aquatic frog Xenopus laevis were determined to be 140± 3 nmol L^-1 gFW^-1hr^-1. Skin tissues were investigated for their ammonia transport properties using a modified Ussing chamber and in vivo-like transepithelial osmotic gradients. Metabolic ammonia generated by the skin accounted to 24±0.2 nmol L^-1 cm^-2 h^-1 (ventral skin) and 28 ±0.2 nmol L^-1 cm^-2 h^-1 (dorsal skin) of which 57% and 51% were released towards the apical bath, respectively. A net ammonia efflux was produced by both skins, where reasonable ammonia net effluxes only occurred when the applied ammonia gradients were above ammonia levels measured in the plasma (0.364±0.033 mM). Quantitative mRNA‐expression analysis revealed that Rhbg is highly expressed in kidney and skin tissues, but showed low expression levels in liver, nerve and muscle tissues. When compared to Rhbg, Rhcg showed 10 times lower relative expression levels in the skin, but 2.5 times higher expression levels in the kidney. When frogs were stressed for 7 days to HEA (1mM NH₄Cl) ammonia excretion rates and blood ammonia levels were similar to unstressed animals. Also skins of ammonia-stressed animals exhibited a net ammonia efflux, with greater ammonia net effluxes measured above blood ammonia concentrations. Interestingly, when exposed to HEA, both ventral and dorsal skins exhibited lower net ammonia efflux rates compared to control tissues.