Chemical heterogeneity of [3H]imipramine binding sites on human platelet membranes.

Functional groups essential for high- and low-affinity [3H]imipramine (IMI) binding were determined by the method of chemical modification. The high-affinity recognition sites contained cysteine and lysine amino acid residues, but not aspartic or glutamic acid residues. The low-affinity recognition sites contained only cysteine residues. Moreover, probably only part of these sites contained these residues. The arginine, tyrosine and histidine residues are not likely to be functionally important for the [3H]IMI binding process. Analysis of the structure-function interaction of drug molecules reveals that, for all substances with high displacement ability, there is a conformation in which they can react with high-affinity IMI recognition sites. Data obtained allowed us to construct a tentative structure model of the high-affinity recognition IMI binding site.

[Imipramine antibodies in endogenous depression in young people]. / Antitela k imipraminu pri éndogennykh depressiiakh iunosheskogo vozrasta.

The drug antibodies were radioimmunologically detected in 58.3% of depressive patients treated with Imipramine. A group of patients with the antibodies permanently present either proved fully resistant or showed a minor effect. A group with antibodies arising just at the start of the treatment displayed either complete remission or substantial improvement. Antibodies were not found in patients exhibiting full recovery or considerable improvement.

High- and low-affinity [3H]imipramine binding sites on human platelets: separate determination and involvement of sulphur-containing bonds.

We have confirmed the presence of two different classes of [3H]imipramine ([3H]IMI) binding sites on human platelets: high-affinity (Kd = 0.52 nM, Bmax = 1670 fmol/mg protein) and low-affinity (Kd = 101 nM, Bmax = 8,000 fmol/mg protein) binding sites. The high-affinity component of [3H]IMI binding can also be obtained separately as the difference between specific [3H]IMI binding in Na-containing and Li-containing incubation buffer. The low-affinity component can be obtained as the difference between [3H]IMI binding in 50 mM Tris-HCl, 5 mM KCl, 120 mM LiCl, (pH 7.5) in the absence and presence of 0.1 mM IMI. The chemical modification of SH groups was performed with Ellman's reagent (10 mM, 40 min at 23 degrees C). The high-affinity component of the binding was totally inhibited while the low-affinity component only decreased by 39%. No decrease in [3H]IMI specific binding was observed when the modification of SH groups was carried out in the presence of 1 microM IMI. The inhibition of high- and low-affinity [3H]IMI binding was reversible since it was completely restored by incubation of modified membranes with 1,4-dithioerythritol (DTE). The reduction of SS groups by DTE (10 mM, 1 h at 23 degrees C) in the intact membrane preparation produced an increase in total number of binding sites of the high-affinity component of [3H]IMI binding by 50%.

[Inhibitors of reverse serotonin uptake and of specific imipramine binding in human blood plasma]. / Ingibitory obratnogo zakhvata serotonina i spetsificheskogo sviazyvaniia imipramina v plazme krovi cheloveka.

Human blood plasma contains low-molecular substances that inhibit in a dose-dependent manner both high-affinity specific binding of imipramine and reverse serotonin uptake by platelets. Incubation of human blood plasma with alumina was made use of to extract and study these imipramine-like inhibitors. The extract obtained from human blood plasma inhibited imipramine binding and reverse uptake of serotonin with median inhibitory concentrations of 0.18 +/- 0.1 and 0.36 +/- 0.15 mg/ml, respectively. After gel chromatography on Biogel P-2 the elution profile of the extract showed 2 major peaks of reverse serotonin uptake and imipramine binding inhibition and 3 additional peaks of reverse serotonin uptake inhibition, which did not have any considerable effect on imipramine specific binding. It is assumed that endogenous inhibitors of imipramine binding and reverse serotonin uptake are involved in the development of affective disorders.

Human plasma inhibitors of platelet serotonin uptake and imipramine receptor binding: extraction and heterogeneity.

Human plasma contains a considerable concentration of low molecular weight substances that inhibit, in a dose-dependent manner, both high-affinity imipramine receptor binding and serotonin uptake in platelets. Incubation of plasma with alumina was used to extract and to partly characterize these imipramine-like inhibitors. The human plasma extract inhibited imipramine binding and serotonin uptake with median inhibitory concentration (IC50) of 0.18 +/- 0.1 and 0.36 +/- 0.15 mg/ml, respectively. Imipramine-like activity of the extract was markedly degraded by carboxypeptidase B and leucine aminopeptidase, but was resistant to neurominidase and phospholipases A2, C, and D. The elution profile of the extract after gel chromatography on Bio-Gel P-2 showed two major peaks of serotonin uptake and imipramine binding inhibition and three additional peaks of serotonin uptake inhibitory activity that did not have a significant effect on imipramine binding. The possible mechanism of pharmacological action of the imipramine-like inhibitors and their relation to development of affective illnesses remain to be clarified.

[Lymphocyte serotonin receptors: a radioreceptor study]. / Serotoninovye retseptory limfotsitov: radioretseptornoe issledovanie.

The radioreceptor method was used to find high affinity, saturable and partially reversible specific binding of 3H-5HT with a gross membrane fraction of human peripheral blood lymphocytes. The Sketchard analysis demonstrated the presence of two types of the binding sites with equilibrium dissociation constants 2 nM and 66 nM. These characteristics are similar to those of 3H-5HT binding with the brain receptors. The results obtained suggest the existence on human lymphocytes of two types of serotonin receptors.