DEVELOPMENTAL CHANGES IN AMPHIBIAN ELECTROLYTE AND ACID-BASE TRANSPORT ACROSS SKIN

ABSTRACT

Larval amphibians tend to be highly aquatic, while the adults tend to be amphibious. During metamorphosis there are changes in the transport of electrolytes, including acids and bases, across skin. Larval anurans have poorly developed cutaneous electrolyte transport systems, and the majority of electrolyte exchange occurs across the gill surfaces. Larval urodeles have skin ion transport systems. However, these appear to be quite different from the ion transport systems found in adults. Based on comparisons of isolated ventral skin studies and whole-animal studies, there may be differences in capacity and/or distribution of Na⁺ transporters in larvae and adults. Allometric analyses of whole animals indicate that larvae exchange ions at a greater rate than adults, while isolated ventral skin preparations show the opposite. Larval urodeles are capable of transporting sodium independently of chloride ions, while adult cutaneous Na⁺ transport requires the presence of CI⁻ in the bath to function normally. Larval urodeles respond to a respiratory acidosis with increased Na⁺ influx and increased transepithelial potential difference, suggesting Na⁺/H⁺ exchange across the skin is increased to excrete the acid load produced by the acidosis. Adults do not increase Na⁺ influx during respiratory acidosis, and decrease their transepithelial potential difference. These results are consistent with electrogenic H⁺ secretion across the skin with a passive redistribution of Na+ and CI⁻ to balance the charge.