Interactions between activators of the larval bullfrog epithelial cation channel (1099.3)

Abstract

The epithelium of the larval bullfrog Rana Catesbeiana contains an apically located non‐selective cation channel. This channel has been shown to be activated by a variety of compounds including acetylcholine (ACh), amiloride and ATP. The purpose of this present study was to further characterize the tadpole channel in terms of interactions between these three ligands at their sites of activation. Tadpole skins were mounted in Ussing chambers with NaCl Ringers bathing the basolateral side. Perfusion of ligands in Ca++ free Ringers was done alone and in various combinations to test for interactions such as potentiation and suppression of ligand effects. ATP was found to potentiate the effects of amiloride and ACh at low concentrations, yet at high concentrations the responses were not additive as would be expected if two different populations of channels were being activated. ACh and amiloride perfusion resulted in a suppression of the ACh response. The addition of two ligands had little effect upon the desensitization time constant. Each of the ligands largly cross‐desensitized the other ligands. These results are consistent with a scenario in which all three ligands activate the same response.