Evidence for the existence of at least two different binding sites for 5HT-reuptake inhibitors within the 5HT-reuptake system from human platelets

Biochem Pharmacol. 1988 Oct 15;37(20):3959-66. doi: 10.1016/0006-2952(88)90080-9.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arsenicals / pharmacology
  • Binding Sites
  • Blood Platelets / metabolism*
  • Carrier Proteins*
  • Cysteine / pharmacology
  • Dithiothreitol / pharmacology
  • Ethylmaleimide / pharmacology
  • Humans
  • Imipramine / metabolism
  • Neurotransmitter Uptake Inhibitors / metabolism*
  • Quinolines / pharmacology
  • Receptors, Drug*
  • Receptors, Neurotransmitter / analysis*
  • Serotonin / metabolism*

Substances

  • Arsenicals
  • Carrier Proteins
  • Neurotransmitter Uptake Inhibitors
  • Quinolines
  • Receptors, Drug
  • Receptors, Neurotransmitter
  • imipramine receptor
  • oxophenylarsine
  • Serotonin
  • EEDQ
  • Cysteine
  • Ethylmaleimide
  • Imipramine
  • Dithiothreitol