Identification of a domain which affects kinetics and antagonistic potency of clozapine at 5-HT3 receptors.

The widely used atypical antipsychotic clozapine is a potent competitive antagonist at 5-HT(3) receptors which may contribute to its unique psychopharmacological profile. Clozapine binds to 5-HT(3) receptors of various species. However, the structural requirements of the respective binding site for clozapine remain to be determined.

Antidepressants and antipsychotic drugs colocalize with 5-HT3 receptors in raft-like domains.

Despite different chemical structure and pharmacodynamic signaling pathways, a variety of antidepressants and antipsychotics inhibit ion fluxes through 5-HT3 receptors in a noncompetitive manner with the exception of the known competitive antagonists mirtazapine and clozapine. To further investigate the mechanisms underlying the noncompetitive inhibition of the serotonin-evoked cation current, we quantified the concentrations of different types of antidepressants and antipsychotics in fractions of sucrose flotation gradients isolated from HEK293 (human embryonic kidney 293) cells stably transfected with the 5-HT3A receptor and of N1E-115 neuroblastoma cells in relation to the localization of the 5-HT3 receptor protein within the cell membrane. Western blots revealed a localization of the 5-HT3 receptor protein exclusively in the low buoyant density (LBD) fractions compatible with a localization within raft-like domains.

Extracellular pH is under circadian control in Gonyaulax polyedra and forms a metabolic feedback loop.

This study investigates the relationship between the circadian clock and metabolism based on recordings of the extracellular pH in cultures of the marine dinoflagellate, Gonyaulax polyedra. In light-dark cycles, pH of the medium rises during the light phase and declines in the dark. The amplitude of this pH-rhythm correlates with light intensity, indicating photosynthesis (and respiration) as the driving force.