“In heterologous cells expressing the dopamine transporter (DAT), simultaneous … intracellular Na(+) and depolarization of the membrane with gramicidin reduced the potency of … substrates, including dopamine, d-amphetamine , beta-phenethylamine, p-tyramine, and MPP(+), in inhibiting binding of the … [(3)H]CFT, with the greatest reduction observed for d-amphetamine.”