Valinomycin strictly uniports K + , thus coupling to valinomycin indicates electrogenic transport of Cl -facilitated by the tested transporter. In contrast to valinomycin, monensin exchanges K + and H + across the phospholipid bilayer, thus coupling to monensin is indicative of the electroneutral symport of Cl -/H + out of the vesicle facilitated by the anion transporter.