The effect of ligand-induced rhythmical structural changes of the artificial receptor 1 on its capacity to mediate ion transport across lipid bilayer membranes was studied. The changes of the intravesicular pH of egg yolk phosphatidylcholine-small unilamellar vesicles (EYPC-SUVs) after application of a transmembrane proton gradient were measured by double-channel fluorescence kinetics in the presence of 1 at various concentrations of the extravesicular ligand Image L-His. Comparison with negative control experiments using Image D-His indicated that increasing concentrations of Image L-His affect the activity of 1 in a presumably rhythmical manner. Compared to the extent of structural rhythmicity, the functional rhythmicity of 1 appeared, however, less significant. The need for refined assay systems to fully delineate the importance of rhythmical activity of 1 with respect to biological rhythmicity is briefly discussed.