Lateral Diffusion of Gαs in the Plasma Membrane Is Decreased after Chronic but not Acute Antidepressant Treatment: Role of Lipid Raft and Non-Raft Membrane Microdomains

Abstract

GPCR signaling is modified both in major depressive disorder and by chronic antidepressant treatment. Endogenous Ga s redistributes from raft-to nonraft-membrane fractions after chronic antidepressant treatment. Modification of G protein anchoring may participate in this process. Regulation of Ga s signaling by antidepressants was studied using fluorescence recovery after photobleaching (FRAP) of GFP-Ga s . Here we find that extended antidepressant treatment both increases the half-time of maximum recovery of GFP-Ga s and decreases the extent of recovery. Furthermore, this effect parallels the movement of Ga s out of lipid rafts as determined by cold detergent membrane extraction with respect to both dose and duration of drug treatment. This effect was observed for several classes of compounds with antidepressant activity, whereas closely related molecules lacking antidepressant activity (eg, R-citalopram) did not produce the effect. These results are consistent with previously observed antidepressant-induced translocation of Ga s , but also suggest an alternate membrane attachment site for this G protein. Furthermore, FRAP analysis provides the possibility of a relatively high-throughput screening tool for compounds with putative antidepressant activity.

Antidepressants Accumulate in Lipid Rafts Independent of Monoamine Transporters to Modulate Redistribution of the G Protein, Gαs

“…These measurements are consistent with the drug time and dose required for G␣ s translocation from rafts, measured either directly (8) or by FRAP (20). Moreover, stereo specificity and the fact that escitalopram does not accumulate over time in HEK cells indicates a specific target (Fig.…”

“…The observed behavior of the antipsychotic, olanzapine, was expected, as it does not move G␣ s out of rafts (20). However, further support for distinct molecular drug targets comes from the enantiomer-selective accumulation of escitalopram, but not the therapeutically inactive enantiomer R-citalopram, and from the finding that that accumulation appears restricted to the SSRIs and MAO inhibitors.…”

“…Treatment with 10 M for 72 h is a standard assay condition (8); however, the effects of these drugs in this cellular system can be observed at concentrations as low as 50 nM after 72 h (20). Culture media and drug were changed daily, and no apparent change in cell morphology was observed during treatment.…”

“…C6 glioma cells were used in these experiments because they do not express monoamine transport proteins (Fig. 1), yet sustained treatment with antidepressant drugs translocates G␣ s from lipid rafts to non-raft regions of the plasma membrane (7,8,20). Furthermore, glia may contribute to both the etiology and the treatment of depression (21,22).…”

“…The accumulation of escitalopram, fluoxetine, and phenelzine, but not R-citalopram or olanzapine, parallels their capacity to mediate the movement of G␣ s from lipid rafts (20). Because neither the tricyclic antidepressants (desipramine, imipramine, and amitriptyline) nor aripiprazole accumulate in rafts, this phenomenon may be class-specific for antidepressants.…”