Induction by low Na + or Cl − of cocaine sensitive carrier‐mediated efflux of amines from cells transfected with the cloned human catecholamine transporters †

COS‐7 cells transfected with the cDNA of the human dopamine transporter (DAT cells) or the human noradrenaline transporter (NAT cells) were loaded with [ 3 H]‐dopamine or [ 3 H]‐noradrenaline and superfused with buffers of different ionic composition. In DAT cells lowering the Na + concentration to 0, 5 or 10 m M caused an increase in 3 H‐efflux. Cocaine (10 μ M ) or mazindol (0.3 μ M ) blocked the efflux at low Na + , but not at 0 Na + . Lowering the Cl − concentration to 0, 5 or 10 m M resulted in an increased efflux, which was blocked by cocaine or mazindol. Desipramine (0.1 μ M ) was without effect in all the conditions tested. In NAT cells, lowering the Na + concentration to 0, 5 or 10 m M caused an increase in 3 H‐efflux, which was blocked by cocaine or mazindol. Desipramine produced a partial block, its action being stronger at 5 or 10 m M Na + than at 0 m M Na + . Efflux induced by 0, 5 or 10 m M Cl − was completely blocked by all three uptake inhibitors. In cross‐loading experiments, 5 m M Na + ‐ or 0 Cl − ‐induced efflux was much lower from [ 3 H]‐noradrenaline‐loaded DAT, than NAT cells and was sensitive to mazindol, but not to desipramine. Efflux from [ 3 H]‐dopamine‐loaded NAT cells elicited by 5 m M Na + or 0 Cl − was blocked by mazindol, as well as by desipramine. Thus, cloned catecholamine transporters display carrier‐mediated efflux of amines if challenged by lowering the extracellular Na + or Cl − , whilst retaining their pharmacological profile. The transporters differ with regard to the ion dependence of the blockade of reverse transport by uptake inhibitors.British Journal of Pharmacology (1997) 121 , 205–212; doi: 10.1038/sj.bjp.0701137