Evidence for the existence of at least two different binding sites for 5HT-reuptake inhibitors within the 5HT-reuptake system from human platelets.
Chemical modification procedures have been used to study the interaction of tricyclic and non-tricyclic 5HT-reuptake inhibitors with the [3H]imipramine binding site (IBS). N-Ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) induced a pronounced loss in [3H]imipramine binding due to a reduction in Bmax. Preincubation with reuptake inhibitors and subsequent inactivation by EEDQ revealed that imipramine and 5HT prevented the EEDQ-induced inhibition, but citalopram and fluoxetine did not. Thiol modification studies demonstrated that reduction by dithiothreitol (DTT) enhanced the binding of [3H]imipramine by increasing the Bmax. The thioselective reagents 1,1-diazobis- (N,N-dimethylformamide) (diamide), phenyl-arsineoxide (PAO) and N-ethylmaleimide (NEM) attenuated the binding capacity by lowering the Bmax. PAO, a reversible thiol reagent, prevented NEM alkylation indicating that dithiols are involved in the NEM-induced inactivation. Binding of tricyclics or non-tricyclics prior to PAO inactivation revealed that tricyclics provide complete protection against thiol modification, while the non-tricyclics do not. The results support the hypothesis that the 5HT-reuptake system of human platelets possesses at least two distinguishable binding sites.
Biessen
E A
EA
Department of Medicinal Chemistry, Subfaculty of Pharmacy, University of Groningen, The Netherlands.
Norder
J A
JA
Horn
A S
AS
Robillard
G T
GT
D001152:Arsenicals / Q000494:pharmacology; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D002352:Carrier Proteins; D003545:Cysteine / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D006801:Humans; D007099:Imipramine / Q000378:metabolism; D014179:Neurotransmitter Uptake Inhibitors / Q000378:metabolism*; D011804:Quinolines / Q000494:pharmacology; D011955:Receptors, Drug; D017981:Receptors, Neurotransmitter / Q000032:analysis*; D012701:Serotonin / Q000378:metabolism*
D001152:Arsenicals; D002352:Carrier Proteins; D014179:Neurotransmitter Uptake Inhibitors; D011804:Quinolines; D011955:Receptors, Drug; D017981:Receptors, Neurotransmitter; C027775:imipramine receptor; C029341:oxophenylarsine; D012701:Serotonin; C000470:EEDQ; D003545:Cysteine; D005033:Ethylmaleimide; D007099:Imipramine; D004229:Dithiothreitol