Cation and local anesthetic conductance induced by the negatively charged ionophore Br-X537A in lipid bilayers.

The cation conductance induced by Br-X537A was measured for K+ and Ca2+ at different pH and different Br-X537A concentrations. The K+-concentration dependence was different depending on the pH of the solution. At pH 4.3, the conductance depended linearly on [K+] while at pH 7 it depended on [K+]2. About the same dependence on [Br-X537A] was found at these pH values. From these results it was concluded that two complexes were transporting K+; at pH greater than or equal to 7 the complex is mostly K2X3- and at pH less than or equal to 5 the complex is mostly KHX3-. From the conductance dependence on [Ca2+], pH, and [Br-X537A] it was found that the only conducting complex is CaX3-. It was also observed that Br-X537A could transport tetracaine. Taking into account the surface charge induced by tetracaine, the conductance depended linearly on the tetracaine concentration. Correcting for the surface charged induced by Br-X537A, the tetracaine conductance was found to depend on [Br-X537A]2. Consequently, the conducting complex is TX2- at pH greater than or equal to 7. No other conducting complexes are formed at the pH is decreased and at pH 4 tetracaine is not conducted. It was found that procaine was not conducted between pH 8 and 4.