Nerve functions require phosphatidylinositol-4,5-bisphosphate (PIP 2 ) that binds to ion channels, thereby controlling their gating. Channel properties are also attributed to serotonin transporters (SERTs); however, SERT regulation by PIP 2 has not been reported. SERTs control neurotransmission by removing serotonin from the extracellular space. An increase in extracellular serotonin results from transporter-mediated efflux triggered by amphetamine-like psychostimulants. Herein, we altered the abundance of PIP 2 by activating phospholipase-C (PLC), using a scavenging peptide, and inhibiting PIP 2 -synthesis. We tested the effects of the verified scarcity of PIP 2 on amphetamine-triggered SERT functions in human cells. We observed an interaction between SERT and PIP 2 in pull-down assays. On decreased PIP 2 availability, amphetamine-evoked currents were markedly reduced compared with controls, as was amphetamineinduced efflux. Signaling downstream of PLC was excluded as a cause for these effects. A reduction of substrate efflux due to PLC activation was also found with recombinant noradrenaline transporters and in rat hippocampal slices. Transmitter uptake was not affected by PIP 2 reduction. Moreover, SERT was revealed to have a positively charged binding site for PIP 2 . Mutation of the latter resulted in a loss of amphetamine-induced SERT-mediated efflux and currents, as well as a lack of PIP 2 -dependent effects. Substrate uptake and surface expression were comparable between mutant and WT SERTs. These findings demonstrate that PIP 2 binding to monoamine transporters is a prerequisite for amphetamine actions without being a requirement for neurotransmitter uptake. These results open the way to target amphetamine-induced SERT-dependent actions independently of normal SERT function and thus to treat psychostimulant addiction.phosphoinositide | reuptake | release | mass spectrometry | amperometry

Actovegin(®) is a biological drug manufactured from a natural source: it is a calf blood hemodialysate. Its therapeutic benefits stem from a variety of pharmacodynamic actions that can be summarized to a common goal, i.e. the enhancement of cellular metabolism; this results from an insulin-like activity mediated by Inositol-phospho-oligosaccharides. Actovegin(®) results in beneficial effects in several pathophysiological clinical settings including malfunction of the blood circulation and trophic disturbances in the brain, impairment of peripheral blood circulation and associated diseases, dermal transplants and acute and chronic wounds. Here, we give an overview of the pharmacodynamic actions of calf-blood hemidialysate and its beneficial effects in a variety of clinical settings.

G protein-coupled receptors have been proposed to exist in signalosomes subject to agonist-driven shifts in the assembly disassembly equilibrium, affected by stabilizing membrane lipids and/or cortical actin restricting mobility. We investigated the highly homologous corticotropin-releasing factor receptors (CRFRs), CRFR1 and -2, which are different within their hydrophobic core. Agonist stimulation of CRFR1 and CRFR2 gave rise to similar concentration-response curves for cAMP accumulation, but CRFR2 underwent restricted collision coupling. Both CRFR1 and CRFR2 formed constitutive oligomers at the cell surface and recruited ␤-arrestin upon agonist activation (as assessed by fluorescence resonance energy transfer microscopy in living cells). However, CRFR2, but not CRFR1, failed to undergo agonist-induced internalization. Likewise, agonist binding accelerated the diffusion rate of CRFR2 only (detected by fluorescence recovery after photobleaching and fluorescence correlation spectroscopy) but reduced the mobile fraction, which is indicative of local confinement. Fluorescence intensity distribution analysis demonstrated that the size of CRFR complexes was not changed. Disruption of the actin cytoskeleton abolished the agonist-dependent increase in CRFR2 mobility, shifted the agonist concentration curve for CRFR2 to the left, and promoted agonist-induced internalization of CRFR2. Our observations are incompatible with an agonist-induced change in monomer-oligomer equilibrium, but they suggest an agonist-induced redistribution of CRFR2 into a membrane microdomain that affords rapid diffusion but restricted mobility and that is stabilized by the actin cytoskeleton. Our data show that membrane anisotropy can determine the shape and duration of receptor-generated signals in a subtypespecific manner.Signal transduction via heterotrimeric G proteins is accomplished by a cycle of activation and deactivation of the G␣-subunit, which is achieved by receptor-catalyzed exchange of prebound GDP for GTP and GTP hydrolysis by the intrinsic GTPase of G␣, respectively. Superimposed on this GTPase cycle, there is a cycle of subunit dissociation and reassociation, in which the inactive heterotrimer G␣.GDP.␤␥ affords receptor docking, GTP binding drives subunit dissociation into G␣.GTP.Mg 2ϩ and G␤␥, and the GTPase-mediated hydrolysis promotes mutual inactivation of two G␣.GDP and G␤␥ by reassociation of the inactive heterotrimer G␣.GDP.␤␥. This model was established some 20 years ago, mainly by the study of reconstituted purified components (Freissmuth et al., 1989). However, since then, methods have become available that allow the tracking of the activity of individual components at the single-cell level. In several instances, these have led to observations that are incompat-

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Monoaminergic neurotransmitters are released into the synaptic cleft by exocytosis; sodium chloride-dependent monoamine transporters like the serotonin transporter (SERT) efficiently clear the synapse of serotonin to stop neurotransmission. Administration of amphetamines (AMPH), induces the reversal of substrate transport. It has been repeatedly shown that inward and outward transport can be independently regulated; phosphorylation of key residues in the amino-terminus is thought to be the responsible mechanism. In our study, we provide evidence for a novel intracellular regulation mechanism of SERT. Depletion of phosphatidylinositol-4,5-bisphosphate (PIP2) reduced AMPH-induced SERT-mediated substrate release specifically. This effect was limited to SERT-mediated efflux because SERT-mediated reuptake was completely unaffected. PIP2 depletion was achieved by activation of phospholipase C (PLC) upon application of 2,4,6-trimethyl-N-[3-(trifluoromethyl)phenyl]benzenesulfonamide (m-3M3FBS; 25 μM), a direct and potent PLC activator. Efflux was determined in a superfusion system that allows for measurement of AMPH-triggered fractional release rates of substrate efflux. Preincubation (10 min) of SERT wild-type-expressing cells with m-3M3FBS led to a significant and concentration-dependent reduction of AMPH-induced efflux. This effect was largely blocked by co-application of U73122 (5 μM; 2 min), a PLC inhibitor. PLC-mediated PIP2 hydrolysation generates inositol-3-phosphate and diacylglycerol and thereby provides downstream effects like protein kinase C (PKC) activation and intracellular calcium rise. Thus we (i) stimulated PKC with PMA (1.0 μM; 10 min), (ii) inhibited with GF109203X (1.0 μM; 10 min) and (iii) chelated Ca 2+ with BAPTA-AM (50 μM; 30 min): There was no effect on efflux with or without m-3M3FBS. This strongly supports the notion that the presence of PIP2 in the immediate vicinity of SERT is essential for the AMPH-induced SERTmediated efflux. HEK cells endogenously express P2Y receptors which activate PLC by G q α. Stimulation of these receptors with ATP and ADP (under suppression of phosphatidylinositol-4-kinase by 30 μM phenylarsineoxide) showed a reduction of release. The trafficking process of SERT was excluded by fluorescence confocal experiments upon administration of m-3M3FBS. Perforated patchclamp recordings on hSERT-expressing HEK cells using m-3M3FBS and PCA showed a significant reduction of membrane current effects compared to control. Additionally, these results provide evidence for the necessity of the presence of PIP2 in the plasma membrane for the AMPHinduced outward configuration of SERT.

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