INDUCTION BY LOW NA- OF COCAINE-SENSITIVE CARRIER-MEDIATED EFFLUX OF AMINES FROM CELLS TRANSFECTED WITH THE CLONED HUMAN CATECHOLAMINE TRANSPORTERS( OR CL)
C. Pifl et al., INDUCTION BY LOW NA- OF COCAINE-SENSITIVE CARRIER-MEDIATED EFFLUX OF AMINES FROM CELLS TRANSFECTED WITH THE CLONED HUMAN CATECHOLAMINE TRANSPORTERS( OR CL), British Journal of Pharmacology, 121(2), 1997, pp. 205-212
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.