INDUCTION BY LOW NA- OF COCAINE-SENSITIVE CARRIER-MEDIATED EFFLUX OF AMINES FROM CELLS TRANSFECTED WITH THE CLONED HUMAN CATECHOLAMINE TRANSPORTERS( OR CL)

1 COS-7 cells transfected with the cDNA of the human dopamine transpor ter (DAT cells) or the human noradrenaline transporter (NAT cells) wer e loaded with [H-3]-dopamine or [H-3]-noradrenaline and superfused wit h buffers of different ionic composition. 2 In DAT cells lowering the Na+ concentration to 0, 5 or 10 mM caused an increase in H-3-efflux. C ocaine (10 mu M) or mazindol (0.3 mu M) blocked the efflux at low Na+, but not at 0 Na+. Lowering the Cl- concentration to 0, 5 or 10 mM res ulted in an increased efflux, which was blocked by cocaine or mazindol . Desipramine (0.1 mu M) was without effect in all the conditions test ed. 3 In NAT cells, lowering the Na+ concentration to 0, 5 or 10 mM ca used an increase in H-3-efflux, which was blocked by cocaine or mazind ol. Desipramine produced a partial block, its action being stronger at 5 or 10 mM Na+ than at 0 mM Na+. Efflux induced by 0, 5 or 10 mM Cl- was completely blocked by all three uptake inhibitors. 4 In cross-load ing experiments, 5 mM Na+- or 0 Cl--induced efflux was much lower from [3H]noradrenaline-loaded DAT, than NAT cells and was sensitive to maz indol, but not to desipramine. Efflux from [H-3]-dopamine-loaded NAT c ells elicited by 5 mM Na+ or 0 Cl- was blocked by mazindol, as well as by desipramine. 5 Thus, cloned catecholamine transporters display car rier-mediated efflux of amines if challenged by lowering the extracell ular Na+ or Cl-, whilst retaining their pharmacological profile. The t ransporters differ with regard to the ion dependence of the blockade o f reverse transport by uptake inhibitors.