“…Most experiments on substrate specificity have been performed with rat OCT1 as well as with rat and human OCT2. Although uptake of radiolabeled cimetidine (2,12), quinidine, and quinine (32) could not be demonstrated, choline (7,10), dopamine (2,6,7,12), epinephrine (2, 12), 5-hydroxytryptamine (5-HT; 2, 6, 12), MPP (2,6,7,12,13,29,52,79), NMN (7), norepinephrine (2,12), TEA (2,7,12,13,72,80), and tyramine (2,12) did show an enhanced tracer uptake in oocytes or cells expressing OCT1, proving the broad substrate specificity of this transporter. As expected for an electrogenic transporter, the addition of potential substrates to OCT1-expressing oocytes resulted in an inward current in voltage-clamped oocytes (6, 7).…”