Effect of rubidium, lithium and cesium on brain ATPase and protein kinases

The authors studied the effect of rubidium, lithium and cesium on the ATPase system and c-AMP protein kinase in brain. They demonstrated that rubidium could replace potassium in the Na+K-ATPase system, whereas lithium and cesium had no effect on this enzyme activity in the absence of potassium. K+-dependent ATPase was activated by even low rubidium concentrations; lithium and cesium inhibited it. None of three (rubidium, lithium and cesium) affected c-AMP protein kinase.

Effect of immobilization stress on tricyclic antidepressant binding and serotonin uptake in rats

Immobilization stress increased the density of imipramine binding sites in platelet and cortical membranes and there was an increased serotonin uptake in platelets. There was a decrease in desipramine binding and noradrenaline uptake in lymphocytes. Our results show that stress acts on the mediator systems in various ways.

Tricyclic antidepressant binding to lymphocyte membranes and changes during depression

The binding of [3H]imipramine, its 2- and 4-nitroderivatives and [3H]desmethylimipramine to lymphocyte membranes was determined. IC50 values for drugs and neurotransmitters to inhibit [3H]imipramine binding to lymphocyte membranes were comparable with those for brain and thrombocyte membranes. The number of [3H]imipramine and [3H]desmethylimipramine binding sites increased in depressive patients, whereas the dissociation constants remained unchanged.

Distribution of cesium in the organism and its effect on the nucleotide metabolism enzymes

After the intraperitoneal administration of 0.5 mEq 134 CsCI . kg -1 to mice, the maximum cesium level in the kidney's, heart, lungs and liver was found in the first hour (T 1/2 13 h), in the muscles after 8 h (T 1/2 180 h), in the brain after 24 h (T 1/2 140 h) and in the blood after 24 h. Maximum cesium levels were found in the muscles. Rats excreted about 17% of the administered dose in 24 h and 38% in 144 h. Most of the cesium (about 90%) is excreted in the urine. In rats, equalization of the plasma and RBC cesium levels takes longer than 6h. Cesium transport is not entirely dependent on the ATPase system, as shown by the results given by the crude mitochondrial fraction with a reduced potassium content. Among the various univalent ions studied, the effect of cesium on creatine kinase, 5'-nucleotidase, phosphodiesterase and deaminase activity was the smallest.

Arginine vasopressin stimulates 32P labeling of phosphoinositides in rat pineal gland

The peptidergic innervation of the pineal gland contains arginine vasopressin (AVP) fibers. Since the site and molecular mechanism of AVP action on the pineal signal transduction has not yet been determined, we examined whether the inositol phosphate transduction system is involved. The phosphoinositide signaling system was studied by measuring metabolic turnover of phosphatidylinositol (PI), phosphatidylinositol phosphate (PIP) and phosphatidylinositol bisphosphate (PIP2), which reflects phosphoinositide cycle activation. AVP induced a significant increase in 32P labeling of PI, PIP and PIP2. The V1 receptor site(s) blocker for AVP abolished enhanced 32P labeling of PIP and PIP2. AVP was without effect on cAMP dependent phosphorylation. The data indicate that AVP activates the phosphoinositide signaling system via V1 receptors and is without effect on the cAMP system.

Methylated and demethylated tricyclic antidepressants and their binding to cell membranes

We studied the binding of methylated and demethylated tricyclic antidepressants (TCA) to synaptic plasma brain membranes (SPM) and to lymphocyte, platelet and erythrocyte membranes. In the synaptic plasma membranes, more demethylated than methylated dibenzazepine derivatives were bound and the binding affinity was decreased. By contrast, in lymphocyte and platelet membranes more methylated derivatives were bound. Phosphatidylserine (PS) enhanced significantly the binding of methylated TCA in SPM without changing the dissociation constant (Kd). Lysophosphatidylserine did not affect the binding. PS also caused an increase of 3H-imipramine binding to lymphocyte membranes but the binding to platelet membranes was not affected. PS also enhanced 3H-5-HT uptake into platelets and 3H-noradrenaline uptake into lymphocytes.

Plasma imipramine levels and demethylase activity in the liver of stressed animals

The steady-state values in rats after a second 14-day period of daily subcutaneous administration of imipramine were the same as during the first period; liver demethylation activity rose for up to 3 days and then returned to normal. The imipramine-binding capacity of the serum, brain myelin, synaptosomes and mitochondria did not alter after repeated administration, but a decrease was found in the red blood cells. Stress (an electric current or immobilization) led to marked reduction of the plasma imipramine level, with a simultaneous increase in liver demethylase activity. Adrenalectomy caused a drop in demethylase activity; stress had no effect either on these values or on imipramine levels.

Liposomes--model membranes to study the binding of tricyclic antidepressants

Binding of four tricyclic antidepressants (TCAs)--imipramine, desipramine, didesmethylimipramine and amitriptyline--on the lipid part of biological membranes was studied. Heterogeneity in partitioning of these drugs in artificial lipid bilayers (liposomes) was quantified using a radioligand binding method. High-affinity binding sites on the liposomes were found and characterized by apparent dissociation constant (Kd) and by binding capacity (Bmax). Change in the membrane lipid composition affected the binding parameters of the high-affinity binding, while the ligand modification affected non-specific binding (low-affinity adsorption) of TCAs. The possible role and methodological importance of high-affinity binding to the lipid part of biological membranes are both discussed. Determination of radioligand binding on model lipid membranes is recommended to avoid certain problems in interpretation of receptor binding studies.

Radioimmunoassay of dibenzazepines and dibenzcycloheptanodienes in body fluids and tissues

In an attempt to establish a radioimmunoassay (RIA), imipramine and amitriptyline immunogens were prepared; desmethyl derivatives were converted into hemisuccinates, conjugated with bovine serum albumin and used for rabbit immunization. [3H]Amitriptyline (4.3 TBq/mmol) and [3H]imipramine (2.9 TBq/mmol) were prepared by catalytic dehalogenation or reductive alkylation. Dibenzazepines and dibenzcycloheptanodienes were determined in biological fluids by a direct method without deproteinization (lower detection limit of 0.5 microgram.l-1); using high-yield methods they were extracted from cell membranes. Assay of tricyclic antidepressants in humans showed that these substances disappear from plasma much earlier than from cell membranes. Dissociation of the antidepressants bound to cell membranes is slow and their plasma concentrations are not influenced by standing for 2 h at 4 degrees C. During preparing the membranes for binding studies these substances are not removed, and they may affect the results of the binding studies.

[Biochemical requirements in tocolysis]

By a specific bond of 3H-dihydroalprenolol the number (Bmax) and characteristic (Kd) of sympathetic beta-receptors in cell membranes of the myometrium and lymphocytes of peripheral blood was assessed. The authors examined six tissue specimens taken during planned termination of pregnancy during the 38th-40th week by primary Caesarean section parallel with a peripheral blood sample. In healthy women even at the end of pregnancy the myometrium contains ample amounts of specific beta-receptors. As compared with the myometrium, the lymphocytes of the peripheral blood contain beta-adrenergic receptors of the same type as the myometrium but in much smaller amounts. So far it was not possible to show a correlation between the number of sympathetic beta-receptors in the membranes of the myometrium and of lymphocytes in the peripheral blood.

[Ca(2+)-channel blockers and binding of tricyclic antidepressive agents]

The interactions between Ca(2+)-channel blockers (verapamil and gallopamil) and synaptic plasma membranes (SPM) from bovine brain or human lymphocyte and platelet plasma membranes were studied. Changes in binding parameters of [3H]imipramine, [3H]desmethylimipramine and [3H]gallopamil were determined after addition of unlabelled verapamil or imipramine and after addition of phosphatidylserine (PS) (PS-stimulation). Specific binding of [3H]imipramine to SPM was decreased and [3H]desmethylimipramine binding was increased by 1 microM verapamil. [3H]gallopamil binds specifically to SPM as well as to platelet and lymphocyte membranes. [3H]gallopamil binding to SPM or lymphocyte plasma membranes was PS-stimulated in contrast to platelet plasma membranes without PS effect on binding. Imipramine inhibited both [3H]gallopamil binding and PS-stimulated [3H]gallopamil binding to SPM or lymphocyte plasma membranes. Mutual effects of tricyclic antidepressants and Ca(2+)-channel blockers on their binding sites require relatively high drug concentrations. Mechanism of Ca(2+)-channel blockers action in the treatment of depression may be connected rather with changes in signal transduction through serotonin and catecholamine receptor systems than with direct interaction of drugs with binding sites for tricyclic antidepressants.

[Adrenergic and serotonergic receptors during depression and its therapy]

It is supposed that adrenergic and serotonergic receptor systems can play a crucial role in pathophysiology of depressive disorder. The hypothesis are based on changes of levels of serotonin and noradrenaline and on changes of their binding sites during depression and its treatment. Study of adrenergic and serotonergic receptors by pharmacological and molecular biological methods give rise to their division to many types and subtypes. This division makes possible to study the depressive disorder and its treatment on well defined receptors systems. Decreased density of beta- and 5-HT1-receptors was found during depression. Antidepressants influence 5-HT2 and adrenergic receptors mainly. Consequently, interaction between adrenergic and serotonergic systems exerts both in the origin of depression and during the treatment. Mutual influence and cooperation of different receptors systems are the main topics of research in this field.