EFFECTS OF CHANGES IN CATION CONCENTRATION NEAR BILAYER LIPID-MEMBRANE ON THE RATE OF CARRIER-MEDIATED CATION FLUXES AND ON THE CARRIER APPARENT SELECTIVITY

A new approach was applied for the measurements of ion transport through bilayer lipid membranes (BLM) induced by electrically neutral cation/H+ exchangers. This is an improved version of the method of the measurements of the cation/H+ exchange rate based on recording pH shifts in the unstirred layers near the BLM. Using this approach, the pH gradient in the unstirred layers induced by the cation/H+ exchanger was reduced by successive addition of the acetate on one side of the BLM until the pH shift reached zero. The difference in acetate concentration across the membrane is a measure of the cation/H+ exchange rate. In the second part of the work we found that the changes in cation concentration in the unstirred layers under the conditions imposed when measuring cation selectivity (according to Antonenko, Yu.N. and Yaguzhinsky, L.S., Biochim. Biophys. Acta 1988; 938, 125-130) can significantly decrease the apparent value of cation selectivity. It was shown that more accurate results can be obtained if low concentrations of the carrier are used. The values of nigericin cation selectivity for the alkali metals were measured (K+/Rb+ 19 ± 1, Rb+/Na+ 1.9 ± 0.2, Na+/Cs+ 8 ± 0.5, Cs+/Li+ 1.8 ± 0.3). © 1990.