Impact of Lipid Raft Integrity on 5-HT3 Receptor Function and its Modulation by Antidepressants

Abstract

Because of the biochemical colocalization of the 5-HT 3 receptor and antidepressants within raft-like domains and their antagonistic effects at this ligand-gated ion channel, we investigated the impact of lipid raft integrity for 5-HT 3 receptor function and its modulation by antidepressants. Treatment with methyl-b-cyclodextrine (MbCD) markedly reduced membrane cholesterol levels and caused a more diffuse membrane distribution of the lipid raft marker protein flotillin-1 indicating lipid raft impairment. Both amplitude and charge of serotonin evoked cation currents were diminished following cholesterol depletion by either MbCD or simvastatin (Sim), whereas the functional antagonistic properties of the antidepressants desipramine (DMI) and fluoxetine (Fluox) at the 5-HT 3 receptor were retained. Although both the 5-HT 3 receptor and flotillin-1 were predominantly found in raft-like domains in western blots following sucrose density gradient centrifugation, immunocytochemistry revealed only a coincidental degree of colocalization of these two proteins. These findings and the persistence of the antagonistic effects of DMI and Fluox against 5-HT 3 receptors after lipid raft impairment indicate that their modulatory effects are likely mediated through non-raft 5-HT 3 receptors, which are not sufficiently detected by means of sucrose density gradient centrifugation. In conclusion, lipid raft integrity appears to be important for 5-HT 3 receptor function in general, whereas it is not a prerequisite for the antagonistic properties of antidepressants such as DMI and Fluox at this ligand-gated ion channel.

Antidepressant Drugs Diversely Affect Autophagy Pathways in Astrocytes and Neurons—Dissociation from Cholesterol Homeostasis

“…More recently developed ADs were designed to specifically impede the activity of neurotransmitter transporters, and are thus called selective serotonin re-uptake inhibitors (SSRIs) or selective serotonin/noradrenalin re-uptake inhibitors (SSNRIs). However, mounting evidence suggests the existence of various additional targets for both, TCAs and SSRIs/NRIs, which may be either supportive for the therapeutic effects, or at the contrary, trigger adverse events (Carvalho et al, 2010;Herr et al, 2003;Nothdurfter et al, 2010;Perisic et al, 2010).…”

Modulation of Ligand-Gated Ion Channels as a Novel Pharmacological Principle

“…The antagonistic potency against the peak amplitude and charge and the Fluox-induced acceleration of receptor desensitization could be shown both under control conditions and after MßCD induced cholesterol depletion (O Fig. 5b, right panel [24]). Immunocytochemistry revealed a more diffuse distribution and signal enhancement of the lipid raft marker protein flotillin-1 upon cholesterol depletion by MßCD or the hydroxyl-methylglutaryl-coenzyme A reductase inhibitor simvastatin (Sim), thereby showing lipid raft impairment (o Fig.…”

“…la[11] and oFig. 5a[24]) When lipid raft integrity was impaired by means of methyl-ß-cyclodextrine (MßCD) induced cholesterol depletion, the DMI induced inhibition and kinetic changes were still retained, although pretreatment with MßCD markedly diminished baseline 5-HT3 receptor currents (oFig. 5a, right panel[24]).…”

“…5a[24]) When lipid raft integrity was impaired by means of methyl-ß-cyclodextrine (MßCD) induced cholesterol depletion, the DMI induced inhibition and kinetic changes were still retained, although pretreatment with MßCD markedly diminished baseline 5-HT3 receptor currents (oFig. 5a, right panel[24]). Comparable findings were obtained, Concentrations of antidepressants (expressed as specific drug concentration [pmol/mg protein]) in sucrose density gradient fractions from HEK-5-HT3A celts pretreated with the respective compounds ( 10 |jm concentrations for 10 min at room temperature).…”

“…Data are shown as mean ± SEM % of control (i.e., without Fluox). Fluox reduces peak amplitude and charge to a similar degree in both experimental conditions, (modified according to [24]). …”