Conducting states of a mammalian serotonin transporter

Mager, Sela; Min, Churl K.; Henry, Douglas J.; Chavkin, Charles; Hoffman, Beth J.; Davidson, Norman; Lester, Henry A.

doi:10.1016/0896-6273(94)90337-9

Cited by 245 publications

(292 citation statements)

References 39 publications

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“…Changes in SERT function and expression have been implicated in anxiety, autism, depression, gastrointestinal disorders, obsessive-compulsive disorder, schizophrenia, substance abuse, and suicide (Lesch and Mossner, 1998). SERTs exhibit several conducting states including a 5HT-independent leak conductance, a 5HT-independent transient conductance, and a 5HT-dependent ionic conductance (Mager et al, 1994). Such conductances have led to the idea that SERTs function in part as ion channels in addition to their role as transporters (Cao et al, 1998;Petersen and DeFelice, 1999).…”

Section: Introductionmentioning

confidence: 99%

Calcium/calmodulin-dependent kinase II regulates the interaction between the serotonin transporter and syntaxin 1A

et al. 2008

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SummaryPlasma membrane serotonin transporters (SERTs) regulate serotonin (5HT) levels in brain and are a site of action of antidepressants and psychostimulant drugs of abuse. Syntaxin 1A is a component of the synaptic vesicle docking and fusion apparatus and has been shown to interact with multiple plasma membrane neurotransmitter transporters including SERT. Previously we showed that syntaxin 1A regulates the transport stoichiometry of SERT. When not bound to syntaxin 1A, SERT shows both substrate-independent Na + fluxes and substrate-dependent Na + fluxes of variable stoichiometry; these fluxes are eliminated in the presence of syntaxin 1A as Na + flux becomes strictly coupled to 5HT uptake. However, not known are the endogenous signaling molecules that determine the conducting states that SERT exhibits. In the present experiments, we show that inhibitors of calcium/calmodulin-dependent kinase II (CaM kinase II) modulate the stoichiometry of 5HT flux and that this effect requires syntaxin 1A. The modulation correlates with a shift in the affinity of SERT for syntaxin 1A binding. The regulation by CaM kinase II is eliminated by a mutation in the N-terminal domain of SERT. In neonatal thalomocortical neurons that endogenously express SERT and syntaxin 1A, inhibition of CaM kinase II reveals SERT-mediated currents. These data suggest that calcium-mediated signals can serve as a trigger for regulating protein-protein interactions that control SERT conducting states.

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Section: Introductionmentioning

confidence: 99%

Calcium/calmodulin-dependent kinase II regulates the interaction between the serotonin transporter and syntaxin 1A

et al. 2008

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“…Recently, several groups have described transporter-associated currents that exceed the predictions of stoichiometric transport Sonders and Amara, 1996). Excess currents have been observed in heterologous expression systems for 5HT Mager et al, 1994), glutamate (Vandenberg et al, 1995;Wadiche et al, 1995a,b), norepinephrine (Galli et al, 1995(Galli et al, , 1996, GABA (Cammack et al, 1994(Cammack et al, , 1996, and dopamine (Sonders et al, 1997) transporters. Similar phenomena appear in native preparations for 5HT (Bruns et al, 1993), GABA (Cammack and Schwartz, 1993), and glutamate (Larson et al, 1996) transporters.…”

Section: Abstract: Serotonin; Transporter; Uptake; Antidepressants;mentioning

confidence: 99%

“…Therefore, discrepancies exist concerning the role of voltage in 5HT uptake. In a heterologous expression system, in which Xenopus oocytes were used to express rat SERTs, Mager et al (1994) observed that 5HT uptake was voltage-independent. In this system, it was also shown that 5 to 12 Na ϩ ions could "escape" into the cell during each transport cycle, thus generating an ionic current in excess of the predicted electroneutrality of coupled transport in mammalian SERTs.…”

Section: Abstract: Serotonin; Transporter; Uptake; Antidepressants;mentioning

confidence: 99%

DrosophilaSerotonin Transporters Have Voltage-Dependent Uptake Coupled to a Serotonin-Gated Ion Channel

et al. 1997

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Serotonin (5HT ) transporters (SERTs) couple to existing ion gradients to transport 5HT into presynaptic terminals. In mammalian SERTs, the transport cycle is reported as electroneutral, with a translocation of zero net charge, and 5HT uptake is independent of membrane voltage. Yet mammalian SERTs exhibit 5HT-induced currents, and Drosophila SERTs (dSERTs) show voltage-dependent uptake. Thus, the relationship between uptake and current remains controversial; furthermore, the number of 5HT molecules translocated per ion channel event is unknown. To investigate this, we have used heterologous expression of cloned dSERTs to measure 5HT flux and dSERT currents concurrently under voltage clamp, and we have used fluctuation analysis to measure the size of the elementary ionic events in the same cells. RNA-injected Xenopus oocytes accumulate 5HT, and paroxetine or desipramine inhibit this uptake. RNA-injected oocytes also display paroxetinesensitive 5HT-induced currents and 5HT-independent leak currents. Na replacement decreases the uptake and the induced currents. 5HT-induced current and 5HT uptake both increase at negative potentials, where 5HT carries ϳ5% of the induced current. Recently, several groups have reported similar phenomena for other transporters, in which transmitter-induced currents exceed the predictions of coupled transport. We now provide evidence that in dSERT, ϳ500 5HT molecules are translocated per channel opening, which, at Ϫ20 mV, carries ϳ10,000 electronic charges. These data support a model in which 500 SERT cycles occur for each 5HT-induced channel opening or a model in which 500 5HT molecules and 10,000 electronic charges pass through a common pore. Key words: serotonin; transporter; uptake; antidepressants; channels; Xenopus oocytesNeurotransmitter transporters couple the gradients of ions to the flux of the transmitter (Amara and Kuhar, 1993;. Na-and Cl-coupled transporters constitute a large family of related proteins that take up GABA, catecholamines, and serotonin (5HT). Na-coupled transporters make up a separate gene family for the uptake of glutamate and aspartate. Recently, several groups have described transporter-associated currents that exceed the predictions of stoichiometric transport Sonders and Amara, 1996). Excess currents have been observed in heterologous expression systems for 5HT Mager et al., 1994), glutamate (Vandenberg et al., 1995; Wadiche et al., 1995a,b), norepinephrine (Galli et al., 1995(Galli et al., , 1996, GABA (Cammack et al., 1994(Cammack et al., , 1996, and dopamine (Sonders et al., 1997) transporters. Similar phenomena appear in native preparations for 5HT (Bruns et al., 1993), GABA (Cammack and Schwartz, 1993), and glutamate (Larson et al., 1996) transporters. Here we report the first data to correlate in the same cells the movement of transmitter with the channel activity underlying the transmitter-induced current. We propose two models that relate this information to voltage-dependent uptake.Serotonin uptake has been characterized by radiolabeled 5HT flu...

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“…Recently, it became apparent that several transporters are involved in additional activities, such as water and ion transport, that may have significant effects on the osmolarity and the membrane potential of certain cells and membranes (Mager et a!., 1994;Loo et a!., 1996;Panayotova-Heiermann et al, 1997;Sonders et al, 1997). This bulk transport of water and/or ions is characteristic of channels, and one of the main open questions is whether the apparent channel activity is also involved in the mechanism of substrate transport.…”

Section: Transporters As Ion Channelsmentioning

confidence: 99%

“…It was possible to demonstrate that serotonin transporter channels are open very rarely relative to the number of catalytic cycles, and it is likely that this uncoupled current is probably not part of the transport process. However, it is important to note that even though serotonin transport is eleetroneutral, inward currents were recorded in ooeytes expressing the serotonin transporter (Mager et at., 1994). As the uncoupled current is influenced by substrate binding or transport, it is difficult to estimate the contribution of each of these processes to the steady-state current during transport.…”

Section: Transporters As Ion Channelsmentioning

confidence: 99%

The Family of Na⁺/Cl⁻ Neurotransmitter Transporters

Nelson

1998

Journal of Neurochemistry

345

192

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Abstract:The termination of neurotransmission is achieved by rapid uptake of the released neurotransmitter by specific high-affinity neurotransmitter transporters. Most of these transporters are encoded by a family of genes (Na~ICI transporters) having a similar membrane topography of 12 transmembrane helices. An evolutionary tree revealed fivedistinct subfamilies: y-aminobutyric acid transporters, monoamine transporters, amino acid transporters, "orphan" transporters, and the recently discovered bacterial transporters. The bacterial transporters that belong to this family may help to develop heterologous expression systems with the aim of solving the threedimensional structure of these membrane proteins. Some of the neurotransmitter transporters have been implicated as important sites for drug action. Monoamine transporters, for example, are targeted by major classes of antidepressants, psychostimulants, and antihypertensive drugs. Localization of individual transporters in specific cells and brain areas is pertinent to understanding their contribution to neurotransmission and their potential as targets for drugs. The most important questions in the field include resolving the mechanism of neurotransmitter transport, the structure of the transporters, and the interaction of each transporter in complex neurological activities.

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Conducting states of a mammalian serotonin transporter

Cited by 245 publications

References 39 publications

Calcium/calmodulin-dependent kinase II regulates the interaction between the serotonin transporter and syntaxin 1A

Calcium/calmodulin-dependent kinase II regulates the interaction between the serotonin transporter and syntaxin 1A

DrosophilaSerotonin Transporters Have Voltage-Dependent Uptake Coupled to a Serotonin-Gated Ion Channel

The Family of Na⁺/Cl⁻ Neurotransmitter Transporters

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Conducting states of a mammalian serotonin transporter

Cited by 245 publications

References 39 publications

Calcium/calmodulin-dependent kinase II regulates the interaction between the serotonin transporter and syntaxin 1A

Calcium/calmodulin-dependent kinase II regulates the interaction between the serotonin transporter and syntaxin 1A

DrosophilaSerotonin Transporters Have Voltage-Dependent Uptake Coupled to a Serotonin-Gated Ion Channel

The Family of Na+/Cl− Neurotransmitter Transporters

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The Family of Na⁺/Cl⁻ Neurotransmitter Transporters