Modulation of ligand-gated ion channels as a novel pharmacological principle.

The present study investigated the functional antagonism of different antidepressants on 5-HT (3) receptor function and the role of lipid rafts for these modulatory effects. Electrophysiological recordings of 5-HT evoked cation currents were recorded with N1E-115 and HEK-5-HT (3A) cells and hippocampal neurons. The characterization of the antagonism of antidepressants was made by the displacement of [ (3)H]GR65630 binding. For membrane fractionation, sucrose density gradient centrifugation was used. Gradient fractions were assayed for antidepressant concentrations by HPLC; 5-HT (3) receptor membrane distribution was determined by Western blot. Colocalization experiments were performed by means of immunocytochemistry. Most antidepressants acted as non-competitive antagonists at the 5-HT (3) receptor. Moreover, some of these compounds were enriched within lipid rafts. Cholesterol depletion impaired lipid raft integrity thereby affecting 5-HT (3) receptor function, whereas the antagonistic effects of antidepressants were not altered.In conclusion, most antidepressants directly antagonize 5-HT (3) receptor activity. 5-HT (3) receptor function PER SE appears to depend on lipid raft integrity, which is, however, not a prerequisite for the modulatory potency of antidepressants at this receptor.