TY - JOUR T1 - Cationic Modulation of Human Dopamine Transporter: Dopamine Uptake and Inhibition of Uptake JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 940 LP - 949 VL - 290 IS - 3 AU - Nianhang Chen AU - Clarence G. Trowbridge AU - Joseph B. Justice, Jr. Y1 - 1999/09/01 UR - http://jpet.aspetjournals.org/content/290/3/940.abstract N2 - Effects of cations on dopamine (DA) uptake into cells expressing the human dopamine transporter and on inhibition of DA uptake by various substrates and inhibitors were investigated by using rotating disk electrode voltammetry. The Na+ dependence of DA uptake varied with Na+ substitutes, hyperbolic with Li+, almost linear at 1 μM DA but hyperbolic at 8 μM DA with choline, and sigmoidal with K+. With Na+substituted by Li+, K[DA]decreased and Vapp remained constant with increasing [Na+], whereasK[Na+] decreased andVapp increased with increasing [DA], suggesting an ordered sequence with Na+binding before DA. Similar trends for the Na+-DA interactions were observed in the presence of cocaine. Cocaine inhibited DA uptake solely by increasing K[DA], with itsKi not significantly different at 55 and 155 mM [Na+], whereas it inhibited Na+stimulation by reducing Vapp more thanK[Na+] at 1 μM DA, andVapp only and less potently at 8 μM DA. Thus, cocaine may compete with DA, not with Na+, for the transporter, and might not follow a strictly ordered reaction with Na+. With Na+ substituted by K+, K[DA] orK[Na+] became insensitive to Na+ or DA. K+ impaired the DA uptake mainly by reducing Vapp, but affected cocaine inhibition by elevating Ki. Despite their different patterns for inhibiting DA uptake, nontransportable inhibitors cocaine, methylphenidate, mazindol, and 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenyl-2-propyl)piperazine (GBR12909) showed similarly modest Na+ dependence in theirKi values. In contrast, substrates DA,m-tyramine, and amphetamine displayed a similarly stronger Na+ requirement for their apparent affinities. The American Society for Pharmacology and Experimental Therapeutics ER -