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