Since the H + /OH -transport is toxic to most living cells, it was of interest to check whether 2 is capable of transporting Cl -selectively, i.e., to equilibrate the Cl -gradient faster than the H + gradient. To test we studied Cl -transport in buffered N-methyl-D-glucamine hydrochloride (NMGD-Cl) solution, using HPTS assay. The NMDG and its cation are considered to be too hydrophilic to be transported across the bilayer, and therefore no pH equilibration should be observed if the transport takes place through electrogenic mechanism only (due to the lack of any charge compensation mechanism). Contrary to these expectations, the activity of 2 under these conditions was significant. This is in agreement with the results described above, which showed that 2 can facilitate H + /Cl -symport (or functionally equivalent OH -/Cl -antiport). However, the activity of 2 was significantly (16 times) enhanced in the presence of gramicidin, a natural cationophore known to very rapidly transport H + (and Na + ) across lipid membranes. Apparently, the onset of the fast charge compensation mechanism speeds up the chloride transport by 2, meaning that 2 transports Cl -much faster than H + or OH -.