Since the same cation gradient was imposed in all experiments and concentrations of all other ions remained constant, the absolute value of the reversal potential is a direct indicator for the selectivity to monovalent cations. Intersection potential was most negative with K+, indicating that permeability to K+ was higher than to the large organic cations. Note also that all values were in the negative voltage range, i.e. closer to the Nernst potential of the cation than to that of the counter-ion, Cl−.