Receptors were added as a DMSO solution (10 µL) at t = 0 and efflux of chloride was measured using a Cl -ion-selective electrode. Detergent was added at t = 300 s to lyse the vesicle and provide a reading for 100% Cl -efflux. Transport activity in KNO3 external solution should correspond to the results of the Cl -/NO3 -exchange assay, whereas activity in KGlu external solution should be significantly reduced. Experiments with a KGlc external solution were repeated in the presence of valinomycin and monensin, separately. The cationophores were added at t = -30 s as a DMSO solution (10 µL, 0.1 mol% loadings, with respect to lipid concentration), before transporters were added as a DMSO solution (10 µL) at t = 0 s. The transporter loading for each receptor was chosen to closely match the respective EC50 value calculated for the Cl -/NO3 -exchange assay.