Interactions between cutaneous ion-exchange mechanisms and acid–base balance in amphibians

Abstract

It has been suspected for over 50 years that amphibian ion exchange involves independent transport of Na+ and Cl− in an inward direction across the skin in exchange for acidic cations and basic anions, respectively. Although a role for such exchange mechanisms has obvious utility in acid–base balance, their participation in this homeostatic process has only recently been documented. We now know that in aquatic Ambystoma tigrinum, the presence of NaCl in the water bathing the skin is required for acid–base regulatory responses to hypercapnia and exercise-induced lactacidosis. Acidotic and alkalotic conditions in the animals' extracellular fluid cause changes in both Na+ and Cl− influx and net flux which are consistent with a role for ion transport in acid–base balance. These processes appear to be under the control of both catecholamines and interrenal steroids.