Anionic and cationic exchange mechanisms in the skin of anurans, with special reference to Leptodactylidae in vivo

Abstract

In several species of anurans, the in vivo skin has been shown to absorb Na ⁺ and Cl ^- independently from dilute external solutions. That the mechanism for sodium absorption is different from that of chloride absroption is born out by the following: (1) Either of these ions is absorbed without an accompanying ion when this latter is impermeant. (2) From NaCl solutions there can be an unequal absorption of sodium and chloride. (3) A selective inhibition of the absorption of one of the ions can be produced experimentally, while the net flux of the other remains unchanged. In all these situations, the absorbed ion has to be exchanged against an endogenous ion of the same charge. In Calyptocephalella gayi , H + and HCO ^- ₃ are exchanged against sodium and chloride respectively. A comparison of the relationships between H ⁺ excretion and Na ⁺ absorption in vivo skins and shortcircuited in vitro skins shows that in the latter no H ⁺ excretion occurs, only the Na ⁺ transport being maintained under these experimental conditions. From this, one must conclude that the active Na ⁺ transport is the motive factor of the transport mechanism. H ⁺ excretion by the in vivo skin plays the role of physiologically short-circuiting the Na ⁺ transport.