Where x is the concentration of the transporter (mol%), y is the Cl -efflux (%) at t = 270 s, the If value at t = 200 s for fluorescencebased studies, and t = 600 s for luminescence-based studies, y0 is the minimum Cl -efflux (%) or If value, y1 is the Cl -efflux (%) or If value at time t, k is the EC50 value in mol%, and n is the Hill coefficient.