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Kinoshita S, Suzuki H, Ito K, Kume K, Shimizu T, Sugiyama Y. Transfected rat cMOAT is functionally expressed on the apical membrane in Madin-Darby canine kidney (MDCK) cells. Pharm Res 1998; 15:1851-6. [PMID: 9892468 DOI: 10.1023/a:1011953906065] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE The purpose of the present study is to investigate the expression of canalicular multispecific organic anion transporter (cMOAT) by its cDNA transfection in polarized Madin-Darby canine kidney cells (MDCK). METHODS MDCK cells were transfected with an expression vector (pCXN2) containing the rat cMOAT cDNA with lipofectamine to obtain the stable transfectant under G418. Cells from a single colony whose cMOAT expression was the highest were seeded to form a tight epithelial monolayer on microporous membrane filters. Export of glutathione S-bimane (GS-B) from monolayers was determined after preloading its precursor, monochloro bimane (MCB). RESULTS A comparable amount of GS-B was excreted to the apical and basal compartments in the vector-transfected cells. In contrast, in cMOAT-transfected cells, the amount apically excreted was approximately twice that excreted into the basal compartment. Cyclosporin A (CsA) (30 microM), an inhibitor of cMOAT at higher concentrations, inhibited the preferential apical export of GS-B from cMOAT-transfected cells. CONCLUSIONS Rat cMOAT is functionally expressed on the apical membrane of MDCK cells after transfection.
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Affiliation(s)
- S Kinoshita
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Japan
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52
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Selz KA, Mandell AJ, Shlesinger MF. Hydrophobic free energy eigenfunctions of pore, channel, and transporter proteins contain beta-burst patterns. Biophys J 1998; 75:2332-42. [PMID: 9788928 PMCID: PMC1299907 DOI: 10.1016/s0006-3495(98)77677-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Hydropathy plots are often used in place of missing physical data to model transmembrane proteins that are difficult to crystallize. The sequential maxima of their graphs approximate the number and locations of transmembrane segments, but potentially useful additional information about sequential hydrophobic variation is lost in this smoothing procedure. To explore a broader range of hydrophobic variations without loss of the transmembrane segment-relevant sequential maxima, we utilize a sequence of linear decompositions and transformations of the n-length hydrophobic free energy sequences, Hi, i = 1...n, of proteins. Constructions of hydrophobic free energy eigenfunctions, psil, from M-lagged, M x M autocovariance matrices, CM, were followed by their all-poles, maximum entropy power spectral, Somega(psil), and Mexican Hat wavelet, Wa,b(psil), transformations. These procedures yielded graphs indicative of inverse frequencies, omega-1, and sequence locations of hydrophobic modes suggestive of secondary and supersecondary protein structures. The graphs of these computations discriminated between Greek Key, Jelly Role, and Up and Down categories of antiparallel beta-barrel proteins. With these methods, examples of porins, connexins, hexose transporters, nuclear membrane proteins, and potassium but not sodium channels appear to belong to the Up and Down antiparallel beta-barrel variety.
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Affiliation(s)
- K A Selz
- Cielo Institute, Asheville, North Carolina 28804, USA.
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53
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Sun AQ, Ananthanarayanan M, Soroka CJ, Thevananther S, Shneider BL, Suchy FJ. Sorting of rat liver and ileal sodium-dependent bile acid transporters in polarized epithelial cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:G1045-55. [PMID: 9815035 DOI: 10.1152/ajpgi.1998.275.5.g1045] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
The rat ileal apical Na+-dependent bile acid transporter (ASBT) and the liver Na+-taurocholate cotransporting polypeptide (Ntcp) are members of a new family of anion transporters. These transport proteins share limited sequence homology and almost identical predicted secondary structures but are localized to the apical surface of ileal enterocytes and the sinusoidal surface of hepatocytes, respectively. Stably transfected Madin-Darby canine kidney (MDCK) cells appropriately localized wild-type ASBT and Ntcp apically and basolaterally as assessed by functional activity and immunocytochemical localization studies. Truncated and chimeric transporters were used to determine the functional importance of the cytoplasmic tail in bile acid transport activity and membrane localization. Two cDNAs were created encoding a truncated transporter in which the 56-amino-acid COOH-terminal tail of Ntcp was removed or substituted with an eight-amino-acid epitope FLAG. For both mutants there was some loss of fidelity in basolateral sorting in that approximately 75% of each protein was delivered to the basolateral surface compared with approximately 90% of the wild-type Ntcp protein. In contrast, deletion of the cytoplasmic tail of ASBT led to complete loss of transport activity and sorting to the apical membrane. An Ntcp chimera in which the 56-amino-acid COOH-terminal tail of Ntcp was replaced with the 40-amino-acid cytoplasmic tail of ASBT was largely redirected (82.4 +/- 3.9%) to the apical domain of stably transfected MDCK cells, based on polarity of bile acid transport activity and localization by confocal immunofluorescence microscopy. These results indicate that a predominant signal for sorting of the Ntcp protein to the basolateral domain is located in a region outside of the cytoplasmic tail. These studies have further shown that a novel apical sorting signal is localized to the cytoplasmic tail of ASBT and that it is transferable and capable of redirecting a protein normally sorted to the basolateral surface to the apical domain of MDCK cells.
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Affiliation(s)
- A Q Sun
- Department of Pediatrics, Mount Sinai School of Medicine, New York, New York 10029, USA
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54
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Ramamoorthy S, Melikian HE, Qian Y, Blakely RD. Biosynthesis, N-glycosylation, and surface trafficking of biogenic amine transporter proteins. Methods Enzymol 1998; 296:347-70. [PMID: 9779460 DOI: 10.1016/s0076-6879(98)96026-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- S Ramamoorthy
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA
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55
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Daniels GM, Amara SG. Selective labeling of neurotransmitter transporters at the cell surface. Methods Enzymol 1998; 296:307-18. [PMID: 9779457 DOI: 10.1016/s0076-6879(98)96023-2] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- G M Daniels
- Department of Cell and Developmental Biology, Vollum Institute for Advanced Biomedical Research, Oregon Health Sciences University, Portland 97201, USA
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56
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Ahn J, Pietrini G, Muth TR, Caplan MJ. Expression of neurotransmitter transport systems in polarized cells. Methods Enzymol 1998; 296:370-88. [PMID: 9779461 DOI: 10.1016/s0076-6879(98)96027-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Affiliation(s)
- J Ahn
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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57
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Blakely RD, Ramamoorthy S, Schroeter S, Qian Y, Apparsundaram S, Galli A, DeFelice LJ. Regulated phosphorylation and trafficking of antidepressant-sensitive serotonin transporter proteins. Biol Psychiatry 1998; 44:169-78. [PMID: 9693389 DOI: 10.1016/s0006-3223(98)00124-3] [Citation(s) in RCA: 148] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Presynaptic serotonin (5-hydroxytryptamine, 5-HT) transporters (SERTs) mediate antidepressant-sensitive clearance of 5-HT following release. Although we have been aware for decades that SERT-mediated 5-HT clearance can be modulated by exogenous agents including serotonin-selective reuptake inhibitors, amphetamines, and cocaine, we have had little reason to speculate that SERT activity was actively controlled through endogenous pathways. Recent studies indicate that SERTs are likely to be trafficked to specific plasma membrane subdomains to achieve localized clearance of 5-HT, and that the number of SERTs resident in the plasma membrane is controlled through kinase- and phosphatase-linked pathways. In particular, roles for protein kinase C and phosphatase 2A become apparent through studies with enzyme activators and inhibitors in SERT-transfected cells, where SERT proteins are rapidly phosphorylated in parallel with transporter redistribution and loss of functional uptake capacity. Based on our findings, and the studies of others in native tissues and transfected cells, we propose a model whereby SERTs are organized in a macromolecular complex in the plasma membrane that may serve to locate reuptake activity near release sites. Although many elements of this model remain hypothetical, our findings suggest a much more dynamic picture of transporter-mediated 5-HT reuptake than typically described and suggest opportunities both for the development of new SERT regulatory agents and for the identification of regulatory pathways that may be compromised in mental illness.
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Affiliation(s)
- R D Blakely
- Department of Pharmacology and Center for Molecular Neuroscience, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA
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58
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Pörzgen P, Bönisch H, Hammermann R, Brüss M. The human noradrenaline transporter gene contains multiple polyadenylation sites and two alternatively spliced C-terminal exons. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1398:365-70. [PMID: 9655936 DOI: 10.1016/s0167-4781(98)00072-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Sequencing downstream of the C-terminal exon 14 of the human noradrenaline transporter (hNAT) gene reveals 5 consensus polyadenylation signals, several adenylate/uridylate-rich elements (AREs) and a new C-terminal exon, designated as exon 15. The tandemly arranged polyadenylation sites are in good conformity with the 3.6- and 5.8-kb hNAT mRNA transcripts. Expression of the alternatively spliced C-terminal exon 15 is shown by RT-PCR. This alternative splicing event proposes additional hNAT mRNA species of 2.4-3 kb in size. Corresponding NAT transcripts are found by Northern analysis of human SKN and rat PC12 cell RNA. Sequence comparison of the hNAT gene to two bovine NAT cDNAs shows the interspecies conservation of this alternative splicing event, the close relationship of human and bovine NAT genes, and implicates a functional role for the transporters C-terminal domain.
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Affiliation(s)
- P Pörzgen
- Institut für Pharmakologie und Toxikologie der Universität Bonn, Reuterstrasse 2b, D-53113 Bonn, Germany
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59
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Fourie AM, Yang Y. Molecular requirements for assembly and intracellular transport of class I major histocompatibility complex molecules. Curr Top Microbiol Immunol 1998; 232:49-74. [PMID: 9557393 DOI: 10.1007/978-3-642-72045-1_3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- A M Fourie
- R. W. Johnson Pharmaceutical Research Institute, San Diego, CA 92121, USA
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60
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Low SH, Roche PA, Anderson HA, van Ijzendoorn SC, Zhang M, Mostov KE, Weimbs T. Targeting of SNAP-23 and SNAP-25 in polarized epithelial cells. J Biol Chem 1998; 273:3422-30. [PMID: 9452464 DOI: 10.1074/jbc.273.6.3422] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
SNAP-23 is the ubiquitously expressed homologue of the neuronal SNAP-25, which functions in synaptic vesicle fusion. We have investigated the subcellular localization of SNAP-23 in polarized epithelial cells. In hepatocyte-derived HepG2 cells and in Madin-Darby canine kidney (MDCK) cells, the majority of SNAP-23 was present at both the basolateral and apical plasma membrane domains with little intracellular localization. This suggests that SNAP-23 does not function in intracellular fusion events but rather as a general plasma membrane t-SNARE. Canine SNAP-23 is efficiently cleaved by the botulinum neurotoxin E, suggesting that it is the toxin-sensitive factor previously found to be involved in plasma membrane fusion in MDCK cells. The localization of SNAP-25 in transfected MDCK cells was studied for comparison and was found to be identical to SNAP-23 with the exception that SNAP-25 was transported to the primary cilia protruding from the apical plasma membrane, which suggests that subtle differences in the targeting signals of both proteins exist. In contrast to its behavior in neurons, the distribution of SNAP-25 in MDCK cells remained unaltered by treatment with dibutyryl cAMP or forskolin, which, however, caused an increased growth of the primary cilia. Finally, we found that SNAP-23/25 and syntaxin 1A, when co-expressed in MDCK cells, do not stably interact with each other but are independently targeted to the plasma membrane and lysosomes, respectively.
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Affiliation(s)
- S H Low
- Department of Anatomy, Cardiovascular Research Institute, University of California, San Francisco, California 94143-0452, USA
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61
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Fanning AS, Anderson JM. PDZ domains and the formation of protein networks at the plasma membrane. Curr Top Microbiol Immunol 1997; 228:209-33. [PMID: 9401208 DOI: 10.1007/978-3-642-80481-6_9] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- A S Fanning
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520-8019, USA
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62
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Le Maout S, Brejon M, Olsen O, Merot J, Welling PA. Basolateral membrane targeting of a renal-epithelial inwardly rectifying potassium channel from the cortical collecting duct, CCD-IRK3, in MDCK cells. Proc Natl Acad Sci U S A 1997; 94:13329-34. [PMID: 9371845 PMCID: PMC24308 DOI: 10.1073/pnas.94.24.13329] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We recently cloned an inward-rectifying K channel (Kir) cDNA, CCD-IRK3 (mKir 2.3), from a cortical collecting duct (CCD) cell line. Although this recombinant channel shares many functional properties with the "small-conductance" basolateral membrane Kir channel in the CCD, its precise subcellular localization has been difficult to elucidate by conventional immunocytochemistry. To circumvent this problem, we studied the targeting of several different epitope-tagged CCD-IRK3 in a polarized renal epithelial cell line. Either the 11-amino acid span of the vesicular stomatitis virus (VSV) G glycoprotein (P5D4 epitope) or a 6-amino acid epitope of the bovine papilloma virus capsid protein (AU1) was genetically engineered on the extreme N terminus of CCD-IRK3. As determined by patch-clamp and two-microelectrode voltage-clamp analyses in Xenopus oocytes, neither tag affected channel function; no differences in cation selectivity, barium block, single channel conductance, or open probability could be distinguished between the wild-type and the tagged constructs. MDCK cells were transfected with tagged CCD-IRK3, and several stable clonal cell lines were generated by neomycin-resistance selection. Immunoprecipitation studies with anti-P5D4 or anti-AU1 antibodies readily detected the predicted-size 50-kDa protein in the transfected cells lines but not in wild-type or vector-only (PcB6) transfected MDCK cells. As visualized by indirect immunofluorescence and confocal microscopy, both the tagged CCD-IRK3 forms were exclusively detected on the basolateral membrane. To assure that the VSV G tag was not responsible for the targeting, the P5D4 epitope modified by a site-directed mutagenesis (Y2F) to remove a potential basolateral targeting signal contained in this tag. VSV(Y2F) was also detected exclusively on the basolateral membrane, confirming bona fide IRK3 basolateral expression. These observations, with our functional studies, suggest that CCD-IRK3 may encode the small-conductance CCD basolateral K channel.
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Affiliation(s)
- S Le Maout
- Department de Biologie Cellulaire et Moleculaire, Centre d'Etudes Saclay, France
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63
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Gu H, Caplan MJ, Rudnick G. Cloned catecholamine transporters expressed in polarized epithelial cells: sorting, drug sensitivity, and ion-coupling stoichiometry. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 1997; 42:175-9. [PMID: 9327872 DOI: 10.1016/s1054-3589(08)60721-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- H Gu
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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64
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The dopamine transporter: comparative ultrastructure of dopaminergic axons in limbic and motor compartments of the nucleus accumbens. J Neurosci 1997. [PMID: 9278525 DOI: 10.1523/jneurosci.17-18-06899.1997] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The dopamine transporter (DAT) regulates extracellular dopamine concentrations, transports neurotoxins, and acts as a substrate for cocaine reinforcement. These functions are known to differ in the limbic-associated shell and motor-associated core compartments of the nucleus accumbens (NAc). Previous studies have shown differential expression of DAT in the NAc shell and core but were limited in resolution to the regional level. Thus, it is not known whether there are differences in the amount, subcellular localization, or plasmalemmal targeting of DAT within individual dopaminergic axons in the two regions. We used high-resolution electron microscopic immunocytochemistry to investigate these possibilities. We show that in both the shell and core, DAT immunogold labeling is present in tyrosine hydroxylase-immunoreactive varicose axons that form symmetric synapses. Within these labeled axons, most DAT gold particles are located on extrasynaptic plasma membranes, but some are associated with intracellular membranes. Dopaminergic axons in the shell contain lower mean densities of both total DAT gold particles (per square micron) and plasmalemmal DAT gold particles (per micron) than those in the core. Within labeled axons in the NAc shell and core, however, there are no detectable differences in the subcellullar distribution of DAT or the percentage of total DAT gold particles that are located on plasma membranes. These studies are the first to examine and compare the subcellular localization of DAT in the NAc shell and core. As a result, they identify intrinsic, cell-specific differences in the expression of DAT within dopaminergic axons in these functionally distinct striatal compartments.
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65
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Ishikawa Y, Eguchi T, Ishida H. Mechanism of beta-adrenergic agonist-induced transmural transport of glucose in rat small intestine. Regulation of phosphorylation of SGLT1 controls the function. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1357:306-18. [PMID: 9268055 DOI: 10.1016/s0167-4889(97)00043-8] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The perfusion of rat small intestine with 10 microM epinephrine (Epi) or 10 microM norepinephrine resulted in significant increases in the amount of 3-O-[methyl-3H]-D-glucose transported from the mucosal to serosal side. The Epi-induced increases in glucose transport were coupled with selective increases in beta-adrenoceptor density in the mucosal membranes. Treatment with 0.1 microM okadaic acid increased glucose transport even in the absence of Epi, but that with 1 microM staurosporine or 60 microM N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide dihydrochloride completely inhibited the increases in glucose transport induced by 10 microM Epi or 10 microM dibutyryl cAMP. The maximal binding sites (Bmax) of [3H]phlorizin in brush border membrane (BBM) from tissues perfused with Epi was increased, showing increases in the binding ability of the Na+/glucose cotransporter (SGLT1) to glucose. Phosphorylation and dephosphorylation of BBM with protein kinase A (PKA) and alkaline phosphatase resulted in increases and decreases in Bmax of [3H]phlorizin, respectively. The phosphorylation state of SGLT1 immunoprecipitated from BBM incubated with [gamma-32P]ATP-Mg2+ and PKA, and the analysis of phosphoamino acids composed of SGLT1 in rats given [32P]orthophosphate indicate the presence of potential sites for PKA-mediated phosphorylation of SGLT1 at serine. These findings indicate that the regulation of phosphorylation of SGLT1 leads to an alteration of its function and results in the control of glucose transport in the rat small intestine.
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Affiliation(s)
- Y Ishikawa
- Department of Pharmacology, Tokushima University School of Dentistry, Kuramoto-cho, Japan.
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66
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Abstract
BACKGROUND Some patients with autosomal recessive limb-girdle muscular dystrophy have mutations in the genes coding for the sarcoglycan proteins (alpha-, beta-, gamma-, and delta-sarcoglycan). To determine the frequency of sarcoglycan-gene mutations and the relation between the clinical features and genotype, we studied several hundred patients with myopathy. METHODS Antibody against alpha-sarcoglycan was used to stain muscle-biopsy specimens from 556 patients with myopathy and normal dystrophin genes (the gene frequently deleted in X-linked muscular dystrophy). Patients whose biopsy specimens showed a deficiency of alpha-sarcoglycan on immunostaining were studied for mutations of the alpha-, beta-, and gamma-sarcoglycan genes with reverse transcription of muscle RNA, analysis involving single-strand conformation polymorphisms, and sequencing. RESULTS Levels of alpha-sarcoglycan were found to be decreased on immunostaining of muscle-biopsy specimens from 54 of the 556 patients (10 percent); in 25 of these patients no alpha-sarcoglycan was detected. Screening for sarcoglycan-gene mutations in 50 of the 54 patients revealed mutations in 29 patients (58 percent): 17 (34 percent) had mutations in the alpha-sarcoglycan gene, 8 (16 percent) in the beta-sarcoglycan gene, and 4 (8 percent) in the gamma-sarcoglycan gene. No mutations were found in 21 patients (42 percent). The prevalence of sarcoglycan-gene mutations was highest among patients with severe (Duchenne-like) muscular dystrophy that began in childhood (18 of 83 patients, or 22 percent); the prevalence among patients with proximal (limb-girdle) muscular dystrophy with a later onset was 6 percent (11 of 180 patients). CONCLUSIONS Defects in the genes coding for the sarcoglycan proteins are limited to patients with Duchenne-like and limb-girdle muscular dystrophy with normal dystrophin and occur in 11 percent of such patients.
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Affiliation(s)
- D J Duggan
- Department of Human Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
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67
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Schroeter S, Levey AI, Blakely RD. Polarized expression of the antidepressant-sensitive serotonin transporter in epinephrine-synthesizing chromaffin cells of the rat adrenal gland. Mol Cell Neurosci 1997; 9:170-84. [PMID: 9245500 DOI: 10.1006/mcne.1997.0619] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Antidepressant-sensitive serotonin (5-hydroxytryptamine, 5HT) transporters (SERTs) clear the amine from extracellular spaces in the CNS and periphery as a mechanism for transmitter inactivation and recycling. Although it is known that SERTs are preferentially expressed on basolateral domains in transfected epithelial cells, details of the transporter's membrane localization in vivo are lacking. 5HT and 5HT receptors have been identified in the rodent adrenal gland. Using SERT antagonist autoradiography, we establish the presence of antidepressant-sensitive transport sites in the rat adrenal medulla. Immunofluorescence experiments using antibodies specific for the SERT COOH and NH2 termini, for 5HT, or for catecholamine biosynthetic enzymes suggest that SERT mediates intra-cellular 5HT accumulation by epinephrine-secreting chromaffin cells. Using confocal microscopy, we establish that SERT expression is nonuniformly distributed along the plasma membrane of chromaffin cells. Notably, SERT immunoreactivity is largely absent from plasma membranes bordering smooth muscle that surrounds vascular sinusoids. Rather, SERT is highly expressed in membranes adjoining other chromaffin cells, consistent with a role for 5HT and SERT in autocrine or paracrine control of chromaffin cell physiology. SNAP-25, a t-SNARE protein implicated in neurotransmitter release, was found to colocalize with SERT. In contrast, Na,K ATPase and NCAM are uniformly distributed along the entire perimeter of chromaffin cell membranes. These findings underscore a role for 5HT and SERT in adrenal physiology, reveal unrecognized polarity of chromaffin cell plasma membranes, and warrant a consideration of common targeting mechanisms localizing amine transporters near release sites.
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Affiliation(s)
- S Schroeter
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA
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