Function, expression, and characterization of the serotonin transporter in the native human intestine

Gill, Ravinder K.; Pant, Nitika; Saksena, Seema; Singla, Anuj; Nazir, Talat M.; Vohwinkel, Lisa; Turner, Jerrold R.; Goldstein, Jay L.; Alrefai, Waddah A.; Dudeja, Pradeep K.

doi:10.1152/ajpgi.00354.2007

Cited by 75 publications

(97 citation statements)

References 29 publications

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“…An original report by Wade et al (44) showed that most SERT was located in the crypts. In contrast, more recent studies in mouse, guinea pig, and human have shown SERT immunoreactivity in many epithelial cells throughout the crypt-villus axis (13,23,28,29) though not in the 5-HT-containing EC cells. How then do the actions of SERT affect the 5-HT signal?…”

Section: Discussionmentioning

confidence: 70%

Serotonin (5-HT) release and uptake measured by real-time electrochemical techniques in the rat ileum

Bertrand

Hu²,

Mach³

et al. 2008

American Journal of Physiology-Gastrointestinal and Liver Physi

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(5-HT) release and uptake measured by real-time electrochemical techniques in the rat ileum. Am J Physiol Gastrointest Liver Physiol 295: G1228 -G1236, 2008. First published October 16, 2008 doi:10.1152/ajpgi.90375.2008 is released from the enterochromaffin cells and plays an important role in regulating intestinal function. Although the release of 5-HT is well documented, the contribution of the serotonin reuptake transporter (SERT) to the levels and actions of 5-HT in the intestine is unclear. This study aimed to demonstrate real-time SERT activity in ileal mucosa and to assess the effects of SERT inhibition using fluoxetine. Electrochemical recordings were made from the mucosa in full-thickness preparations of rat ileum using a carbon fiber electrode to measure 5-HT oxidation current and a force transducer to record circular muscle (CM) tension. Compression of the mucosa stimulated a peak 5-HT release of 12 Ϯ 6 M, which decayed to 7 Ϯ 4 M. Blockade of SERT with fluoxetine (1 M) increased the peak compression-evoked release to 19 Ϯ 9 M, and the background levels of 5-HT increased to 11 Ϯ 7 M (P Ͻ 0.05, n ϭ 7). When 5-HT was exogenously applied to the mucosa, fluoxetine caused a significant increase in the time to 50% and 80% decay of the oxidation current. Fluoxetine also increased the spontaneous CM motility (P Ͻ 0.05; n ϭ 7) but did not increase the CM contraction-evoked 5-HT release (P Ͼ 0.05, n ϭ 5). In conclusion, this is the first characterization of the real-time uptake of 5-HT into the rat intestine. These data suggest that SERT plays an important role in the modulation of 5-HT concentrations that reach intestinal 5-HT receptors. electrochemistry; enterochromaffin cell; gastrointestinal tract; serotonin reuptake transporter is produced and stored in the enterochromaffin (EC) cells of the intestinal epithelium (19, 34). Released 5-HT acts as a sensory mediator and plays an important role in visceral sensation and in regulating gut function by activating 5-HT receptors on the afferent nerve terminals (1,22,26). Activation of the intrinsic sensory neurons of the enteric nervous system by 5-HT is responsible for initiating or enhancing local intestinal motor reflexes (11,(42)(43)(44) and for increasing secretory function (e.g., 39). EC-derived 5-HT also activates extrinsic afferent fibers and thus contributes to the relay of sensory information to the central nervous system (24,25,41).The actions of 5-HT are terminated by uptake via the serotonin reuptake transporter (SERT, a Na ϩ /Cl Ϫ -dependent transporter) (31). SERT is the target for many important therapeutic drugs such as Prozac (fluoxetine), a member of the serotonin-selective reuptake inhibitors. SERT has been localized to many intestinal epithelial cells using immunohistochemistry to detect protein (44) and Northern blots to detect mRNA (13). The SERT gene is subject to a number of naturally occurring polymorphisms in the coding and promoter regions, some of which have been linked to the symptoms of irritable bowel syndrome (IBS) (e.g., 46) or ...

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Section: Discussionmentioning

confidence: 70%

Serotonin (5-HT) release and uptake measured by real-time electrochemical techniques in the rat ileum

Bertrand

Hu²,

Mach³

et al. 2008

American Journal of Physiology-Gastrointestinal and Liver Physi

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“…Hence, other proteins known to transport cations were considered, and SERT was chosen for further investigation for reasons outlined subsequently. SERT is expressed in both AP and BL membranes, although expression on the AP side is predominant in the intestine and Caco-2 cell monolayers (Wade et al, 1996;Martel et al, 2003;Gill et al, 2008), and it functions as an uptake transporter (Nelson and Rudnick, 1979). The endogenous substrate of SERT is serotonin; however, SERT and other OCTs share substrates.…”

Section: Discussionmentioning

confidence: 99%

Four Cation-Selective Transporters Contribute to Apical Uptake and Accumulation of Metformin in Caco-2 Cell Monolayers

Han

Proctor

Costales

et al. 2015

J Pharmacol Exp Ther

107

123

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Metformin is the frontline therapy for type II diabetes mellitus. The oral bioavailability of metformin is unexpectedly high, between 40 and 60%, given its hydrophilicity and positive charge at all physiologic pH values. Previous studies in Caco-2 cell monolayers, a cellular model of the human intestinal epithelium, showed that during absorptive transport metformin is taken up into the cells via transporters in the apical (AP) membrane; however, predominant transport to the basolateral (BL) side occurs via the paracellular route because intracellular metformin cannot egress across the BL membrane. Furthermore, these studies have suggested that the AP transporters can contribute to intestinal accumulation and absorption of metformin. Transporter-specific inhibitors as well as a novel approach involving a cocktail of transporter inhibitors with overlapping selectivity were used to identify the AP transporters that mediate metformin uptake in Caco-2 cell monolayers; furthermore, the relative contributions of these transporters in metformin AP uptake were also determined. The organic cation transporter 1, plasma membrane monoamine transporter (PMAT), serotonin reuptake transporter, and choline high-affinity transporter contributed to approximately 25%, 20%, 20%, and 15%, respectively, of the AP uptake of metformin. PMATknockdown Caco-2 cells were constructed to confirm the contribution of PMAT in metformin AP uptake because a PMAT-selective inhibitor is not available. The identification of four intestinal transporters that contribute to AP uptake and potentially intestinal absorption of metformin is a significant novel finding that can influence our understanding of metformin pharmacology and intestinal drug-drug interactions involving this highly prescribed drug.

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“…Previously, we demonstrated that PKA-dependent posttranslational modification of transcription factors Sp1 and Sp3 and their reduced DNA-binding activity may be responsible for the repression of NHE3 transcriptional activity by TNF-␣ and IFN-␥ (4). Furthermore, our recent studies showed that PKC␣ activation by serotonin leads to repression of both transcriptional and functional activity of NHE3 in intestinal epithelial cells (3,15). The role of PKC␦ and ERK1/2 as positive Fig.…”

Section: Discussionmentioning

confidence: 92%

PKCδ-dependent activation of ERK1/2 leads to upregulation of the human NHE2 transcriptional activity in intestinal epithelial cell line C2BBe1

Muthusamy

Shukla

Amin

et al. 2012

American Journal of Physiology-Gastrointestinal and Liver Physi

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Muthusamy S, Shukla S, Amin Md. R, Cheng M, Orenuga T, Dudeja PK, Malakooti J. PKC␦-dependent activation of ERK1/2 leads to upregulation of the human NHE2 transcriptional activity in intestinal epithelial cell line C2BBe1. Am J Physiol Gastrointest Liver Physiol 302: G317-G325, 2012. First published November 3, 2011; doi:10.1152/ajpgi.00363.2011.-The apical Na ϩ /H ϩ exchanger (NHE) isoform NHE2 is involved in transepithelial Na ϩ absorption in the intestine. Our earlier studies have shown that mitogenic agent phorbol 12-myristate 13-acetate (PMA) induces the expression of NHE2 through activation of transcription factor early growth response-1 (Egr-1) and its interactions with the NHE2 promoter. However, the signaling pathways involved in transcriptional stimulation of NHE2 in response to PMA in the intestinal epithelial cells are not known. Chemical inhibitors and genetic approaches were used to investigate the signaling pathways responsible for the stimulation of NHE2 expression by PMA via Egr-1 induction. We show that, in response to PMA, PKC␦, a member of novel PKC isozymes, and MEK-ERK1/2 pathway of mitogen-activated protein kinases stimulate the NHE2 expression in C2BBe1 intestinal epithelial cells. PMA rapidly and transiently induced activation of PKC␦. Small inhibitory RNA-mediated knockdown of PKC␦ blocked the stimulatory effect of PMA on the NHE2 promoter activity. In addition, blockade of PKC␦ by rottlerin, a PKC␦-specific inhibitor, and ERK1/2 by U0126, a MEK-ERK inhibitor, abrogated PMA-induced Egr-1 expression. Immunofluorescence studies revealed that inhibition of ERK1/2 activation prevents translocation of PMA-induced Egr-1 into the nucleus. Consistent with these data, PMA-induced Egr-1 interaction with the NHE2 promoter region was prevented in nuclear extracts from U0126-pretreated cells. In conclusion, our data provide the first evidence that the stimulatory effect of PMA on NHE2 expression is mediated through the initial activation of PKC␦, subsequent PKC␦-dependent activation of MEK-ERK1/2 signaling pathway, and stimulation of Egr-1 expression. Furthermore, we show that transcription factor Egr-1 acts as an intermediate effector molecule that links the upstream signaling cues to the long-term stimulation of NHE2 expression by PMA in C2BBe1 cells. Naϩ /H ϩ exchanger; signal transduction pathway; phorbol 12-myristate 13-acetate; early growth response-1

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Function, expression, and characterization of the serotonin transporter in the native human intestine

Cited by 75 publications

References 29 publications

Serotonin (5-HT) release and uptake measured by real-time electrochemical techniques in the rat ileum

Serotonin (5-HT) release and uptake measured by real-time electrochemical techniques in the rat ileum

Four Cation-Selective Transporters Contribute to Apical Uptake and Accumulation of Metformin in Caco-2 Cell Monolayers

PKCδ-dependent activation of ERK1/2 leads to upregulation of the human NHE2 transcriptional activity in intestinal epithelial cell line C2BBe1

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