The mechanism of the chloride transport processes mediated by anionophores 3-5 and 8-10 were investigated using complementary cationophore coupled assays (Figure ). POPC vesicles were loaded with 300 mM KCl and suspended in a 300 mM solution of either potassium gluconate (KGlc) or KNO3, buffered to pH 7.20 with potassium phosphate salts. Gluconate cannot be transported across the bilayer because it is large and polar; thus, compound-mediated Cl -transport is dependent on coupling to either valinomycin or monensin. Both cationophores transport K + across the bilayer via different mechanisms and indicate different modes of Cl -transport.