Ammonia permeability through membranes in living organisms is especially of medical and pharmacological interest because high blood levels of ammonia is hazardous to health and can lead to d eath . The nature has developed several ways to transport ammonia through membranes in order to recycle it. Even in plants an equitable ammon ia concentration inside cells is crucial for vegetation and metabolism. An essential component for guaranteeing a functional ammonia balance are integrated membrane channel proteins, the Aquaporines. The knowledge about permeabilities in some of them is still missing and discussed, like for the plant aqua-ammonia-porine AtTIP2;1. Due to the fact that this protein is most likely ammonia permeable and alternative approaches like planar lipid bilayer measurements are challenging, a novel vesicle assay based on pH sensitive measurements will be presented. With this assay it is possible to estimate flux rates of weak bases considering stoichiometries and limiting deprotonation effects. The functionality of this assay could be proved using different ionophores by estimating corresponding permeabilities. For this purpose, the model solves a set of differential equations to evaluate corresponding channel turnover numbers with Mathematica. It could be shown that predicted model curves were consistent with the experimental outcome. Thus, the theoretical model can be compared to the results and used to obtain useful measuring conditions for experiments. In a first attempt, a preliminary upper limit of ammonia permeability from AtTIP2;1 was found, 5.58 · 10 15 m/s.