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Kok M, Brodsky JL. The biogenesis of potassium transporters: implications of disease-associated mutations. Crit Rev Biochem Mol Biol 2024:1-45. [PMID: 38946646 DOI: 10.1080/10409238.2024.2369986] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2024] [Accepted: 06/16/2024] [Indexed: 07/02/2024]
Abstract
The concentration of intracellular and extracellular potassium is tightly regulated due to the action of various ion transporters, channels, and pumps, which reside primarily in the kidney. Yet, potassium transporters and cotransporters play vital roles in all organs and cell types. Perhaps not surprisingly, defects in the biogenesis, function, and/or regulation of these proteins are linked to range of catastrophic human diseases, but to date, few drugs have been approved to treat these maladies. In this review, we discuss the structure, function, and activity of a group of potassium-chloride cotransporters, the KCCs, as well as the related sodium-potassium-chloride cotransporters, the NKCCs. Diseases associated with each of the four KCCs and two NKCCs are also discussed. Particular emphasis is placed on how these complex membrane proteins fold and mature in the endoplasmic reticulum, how non-native forms of the cotransporters are destroyed in the cell, and which cellular factors oversee their maturation and transport to the cell surface. When known, we also outline how the levels and activities of each cotransporter are regulated. Open questions in the field and avenues for future investigations are further outlined.
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Affiliation(s)
- Morgan Kok
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
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A biophysical perspective of the regulatory mechanisms of ezrin/radixin/moesin proteins. Biophys Rev 2022; 14:199-208. [PMID: 35340609 PMCID: PMC8921360 DOI: 10.1007/s12551-021-00928-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Accepted: 12/14/2021] [Indexed: 02/08/2023] Open
Abstract
Many signal transductions resulting from ligand-receptor interactions occur at the cell surface. These signaling pathways play essential roles in cell polarization, membrane morphogenesis, and the modulation of membrane tension at the cell surface. However, due to the large number of membrane-binding proteins, including actin-membrane linkers, and transmembrane proteins present at the cell surface, the molecular mechanisms underlying the regulation at the cell surface are yet unclear. Here, we describe the molecular functions of one of the key players at the cell surface, ezrin/radixin/moesin (ERM) proteins from a biophysical point of view. We focus our discussion on biophysical properties of ERM proteins revealed by using biophysical tools in live cells and in vitro reconstitution systems. We first describe the structural properties of ERM proteins and then discuss the interactions of ERM proteins with PI(4,5)P2 and the actin cytoskeleton. These properties of ERM proteins revealed by using biophysical approaches have led to a better understanding of their physiological functions in cells and tissues. Supplementary Information The online version contains supplementary material available at 10.1007/s12551-021-00928-0.
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Chivasso C, Hagströmer CJ, Rose KL, Lhotellerie F, Leblanc L, Wang Z, Moscato S, Chevalier C, Zindy E, Martin M, Vanhollebeke B, Gregoire F, Bolaky N, Perret J, Baldini C, Soyfoo MS, Mattii L, Schey KL, Törnroth-Horsefield S, Delporte C. Ezrin Is a Novel Protein Partner of Aquaporin-5 in Human Salivary Glands and Shows Altered Expression and Cellular Localization in Sjögren's Syndrome. Int J Mol Sci 2021; 22:ijms22179213. [PMID: 34502121 PMCID: PMC8431299 DOI: 10.3390/ijms22179213] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 08/19/2021] [Accepted: 08/23/2021] [Indexed: 12/01/2022] Open
Abstract
Sjögren’s syndrome (SS) is an exocrinopathy characterized by the hypofunction of salivary glands (SGs). Aquaporin-5 (AQP5); a water channel involved in saliva formation; is aberrantly distributed in SS SG acini and contributes to glandular dysfunction. We aimed to investigate the role of ezrin in AQP5 mislocalization in SS SGs. The AQP5–ezrin interaction was assessed by immunoprecipitation and proteome analysis and by proximity ligation assay in immortalized human SG cells. We demonstrated, for the first time, an interaction between ezrin and AQP5. A model of the complex was derived by computer modeling and in silico docking; suggesting that AQP5 interacts with the ezrin FERM-domain via its C-terminus. The interaction was also investigated in human minor salivary gland (hMSG) acini from SS patients (SICCA-SS); showing that AQP5–ezrin complexes were absent or mislocalized to the basolateral side of SG acini rather than the apical region compared to controls (SICCA-NS). Furthermore, in SICCA-SS hMSG acinar cells, ezrin immunoreactivity was decreased at the acinar apical region and higher at basal or lateral regions, accounting for altered AQP5–ezrin co-localization. Our data reveal that AQP5–ezrin interactions in human SGs could be involved in the regulation of AQP5 trafficking and may contribute to AQP5-altered localization in SS patients
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Affiliation(s)
- Clara Chivasso
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium; (C.C.); (F.L.); (L.L.); (F.G.); (N.B.); (J.P.)
| | - Carl Johan Hagströmer
- Division of Biochemistry and Structural Biology, Lund University, 221 00 Lund, Sweden;
| | - Kristie L. Rose
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37240, USA; (K.L.R.); (Z.W.); (K.L.S.)
| | - Florent Lhotellerie
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium; (C.C.); (F.L.); (L.L.); (F.G.); (N.B.); (J.P.)
| | - Lionel Leblanc
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium; (C.C.); (F.L.); (L.L.); (F.G.); (N.B.); (J.P.)
| | - Zhen Wang
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37240, USA; (K.L.R.); (Z.W.); (K.L.S.)
| | - Stefania Moscato
- Department of Clinical and Experimental Medicine, University of Pisa, 56126 Pisa, Italy; (S.M.); (C.B.); (L.M.)
| | - Clément Chevalier
- Center for Microscopy and Molecular Imaging (CMMI), 6041 Gosselies, Belgium; (C.C.); (E.Z.)
| | - Egor Zindy
- Center for Microscopy and Molecular Imaging (CMMI), 6041 Gosselies, Belgium; (C.C.); (E.Z.)
| | - Maud Martin
- Laboratory of Neurovascular Signaling, Université Libre de Bruxelles, 6041 Gosselies, Belgium; (M.M.); (B.V.)
| | - Benoit Vanhollebeke
- Laboratory of Neurovascular Signaling, Université Libre de Bruxelles, 6041 Gosselies, Belgium; (M.M.); (B.V.)
| | - Françoise Gregoire
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium; (C.C.); (F.L.); (L.L.); (F.G.); (N.B.); (J.P.)
| | - Nargis Bolaky
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium; (C.C.); (F.L.); (L.L.); (F.G.); (N.B.); (J.P.)
| | - Jason Perret
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium; (C.C.); (F.L.); (L.L.); (F.G.); (N.B.); (J.P.)
| | - Chiara Baldini
- Department of Clinical and Experimental Medicine, University of Pisa, 56126 Pisa, Italy; (S.M.); (C.B.); (L.M.)
| | | | - Letizia Mattii
- Department of Clinical and Experimental Medicine, University of Pisa, 56126 Pisa, Italy; (S.M.); (C.B.); (L.M.)
| | - Kevin L. Schey
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37240, USA; (K.L.R.); (Z.W.); (K.L.S.)
| | - Susanna Törnroth-Horsefield
- Division of Biochemistry and Structural Biology, Lund University, 221 00 Lund, Sweden;
- Correspondence: (S.T.-H.); (C.D.)
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium; (C.C.); (F.L.); (L.L.); (F.G.); (N.B.); (J.P.)
- Correspondence: (S.T.-H.); (C.D.)
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Abstract
PURPOSE OF REVIEW The apical Na/K/2Cl cotransporter (NKCC2) mediates NaCl reabsorption by the thick ascending limb, contributing to maintenance of blood pressure (BP). Despite effective NKCC2 inhibition by loop diuretics, these agents are not viable for long-term management of BP due to side effects. Novel molecular mechanisms that control NKCC2 activity reveal an increasingly complex picture with interacting layers of NKCC2 regulation. Here, we review the latest developments that shine new light on NKCC2-mediated control of BP and potential new long-term therapies to treat hypertension. RECENT FINDINGS Emerging molecular NKCC2 regulators, often binding partners, reveal a complex overlay of interacting mechanisms aimed at fine tuning NKCC2 activity. Different factors achieve this by shifting the balance between trafficking steps like exocytosis, endocytosis, recycling and protein turnover, or by balancing phosphorylation vs. dephosphorylation. Further molecular details are also emerging on previously known pathways of NKCC2 regulation, and recent in-vivo data continues to place NKCC2 regulation at the center of BP control. SUMMARY Several layers of emerging molecular mechanisms that control NKCC2 activity may operate simultaneously, but they can also be controlled independently. This provides an opportunity to identify new pharmacological targets to fine-tune NKCC2 activity for BP management.
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Abstract
Moesin is expressed in several types of cells including epithelial and endothelial cells. Several groups reported that moesin plays important roles in the regulation of the cellular motility, and the process of internalization of membrane proteins. However, the physiological roles of moesin in the kidney still remain unclear. Herein, we examined the physiological function of moesin in the kidney using moesin knockout (Msn -/y ) mice. There was no obvious abnormality in the renal morphology of Msn -/y mice. However, we found that Msn -/y mice exhibited mild hyperchloremia, and reduced glomerular filtration rate compared to wild type (WT) mice. Absolute electrolytes excretions of NaCl in Msn -/y mice were not significantly changed compared to WT mice. In the renal medulla, moesin was detected in thick ascending limb of Henle (TALH) as previously reported. To determine the physiological function of moesin in TALH, we examined the expression and subcellular localization of NKCC2 in Msn -/y mice. Interestingly, apical surface expression level, but not total expression of NKCC2 was increased in Msn -/y mice. Subcellular fractionation of renal medulla lysate and internalization assay using tubular suspension showed that the process of NKCC2 endocytosis is impaired. Since the distribution of NKCC2 in lipid raft fractions was decreased in Msn -/y mice, moesin may regulate the NKCC2 distribution to microdomain. These results suggest that moesin regulates the internalization of NKCC2. Furthermore, euhydration by water loading caused hyponatremina in Msn -/y mice, suggesting that dysfunction of moesin is associated with the nephrogenic syndrome of inappropriate antidiuresis (NSIAD).
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Kawaguchi K, Yoshida S, Hatano R, Asano S. Pathophysiological Roles of Ezrin/Radixin/Moesin Proteins. Biol Pharm Bull 2017; 40:381-390. [PMID: 28381792 DOI: 10.1248/bpb.b16-01011] [Citation(s) in RCA: 72] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ezrin/radixin/moesin (ERM) proteins function as general cross-linkers between plasma membrane proteins and the actin cytoskeleton and are involved in the functional expression of membrane proteins on the cell surface. They also integrate Rho guanosine 5'-triphosphatase (GTPase) signaling to regulate cytoskeletal organization by sequestering Rho-related proteins. They act as protein kinase A (PKA)-anchoring proteins and sequester PKA close to its target proteins for their effective phosphorylation and functional regulation. Therefore, ERM proteins seem to play important roles in the membrane transport of electrolytes by ion channels and transporters. In this review, we focus on the pathophysiological roles of ERM proteins in in vivo studies and introduce the phenotypes of their knockout and knockdown mice.
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Affiliation(s)
- Kotoku Kawaguchi
- Department of Molecular Physiology, College of Pharmaceutical Sciences, Ritsumeikan University
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Singh R, Kursan S, Almiahoub MY, Almutairi MM, Garzón-Muvdi T, Alvarez-Leefmans FJ, Di Fulvio M. Plasma Membrane Targeting of Endogenous NKCC2 in COS7 Cells Bypasses Functional Golgi Cisternae and Complex N-Glycosylation. Front Cell Dev Biol 2017; 4:150. [PMID: 28101499 PMCID: PMC5209364 DOI: 10.3389/fcell.2016.00150] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 12/14/2016] [Indexed: 12/04/2022] Open
Abstract
Na+K+2Cl− co-transporters (NKCCs) effect the electroneutral movement of Na+-K+ and 2Cl− ions across the plasma membrane of vertebrate cells. There are two known NKCC isoforms, NKCC1 (Slc12a2) and NKCC2 (Slc12a1). NKCC1 is a ubiquitously expressed transporter involved in cell volume regulation, Cl− homeostasis and epithelial salt secretion, whereas NKCC2 is abundantly expressed in kidney epithelial cells of the thick ascending loop of Henle, where it plays key roles in NaCl reabsorption and electrolyte homeostasis. Although NKCC1 and NKCC2 co-transport the same ions with identical stoichiometry, NKCC1 actively co-transports water whereas NKCC2 does not. There is growing evidence showing that NKCC2 is expressed outside the kidney, but its function in extra-renal tissues remains unknown. The present study shows molecular and functional evidence of endogenous NKCC2 expression in COS7 cells, a widely used mammalian cell model. Endogenous NKCC2 is primarily found in recycling endosomes, Golgi cisternae, Golgi-derived vesicles, and to a lesser extent in the endoplasmic reticulum. Unlike NKCC1, NKCC2 is minimally hybrid/complex N-glycosylated under basal conditions and yet it is trafficked to the plasma membrane region of hyper-osmotically challenged cells through mechanisms that require minimal complex N-glycosylation or functional Golgi cisternae. Control COS7 cells exposed to slightly hyperosmotic (~6.7%) solutions for 16 h were not shrunken, suggesting that either one or both NKCC1 and NKCC2 may participate in cell volume recovery. However, NKCC2 targeted to the plasma membrane region or transient over-expression of NKCC2 failed to rescue NKCC1 in COS7 cells where NKCC1 had been silenced. Further, COS7 cells in which NKCC1, but not NKCC2, was silenced exhibited reduced cell size compared to control cells. Altogether, these results suggest that NKCC2 does not participate in cell volume recovery and therefore, NKCC1 and NKCC2 are functionally different Na+K+2Cl− co-transporters.
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Affiliation(s)
- Richa Singh
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Shams Kursan
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Mohamed Y Almiahoub
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Mohammed M Almutairi
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Tomás Garzón-Muvdi
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Francisco J Alvarez-Leefmans
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Mauricio Di Fulvio
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
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Na+/K+-ATPase β1-subunit is recruited in Na-K-2Cl co-transporter isoform 2 multiprotein complexes in rat kidneys: possible role in blood pressure regulation. J Hypertens 2016; 32:1842-53. [PMID: 24927069 DOI: 10.1097/hjh.0000000000000258] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
OBJECTIVE The progression from prehypertensive to hypertensive state in spontaneous hypertensive rats (SHRs) is accompanied by a significant increase in membrane expression of Na-K-2Cl co-transporter isoform 2 (NKCC2), suggesting that the altered NKCC2 trafficking and activity are directly related with the development of hypertension in this strain. The aim of this work is to gain insights on the molecular mechanism that underlies this phenomenon. METHODS We performed a comparative analysis of NKCC2 multiprotein complexes (MPCs) in the kidney of SHRs versus Wistar Kyoto rats by Blue Native difference gel electrophoresis combined with mass spectrometry. RESULTS We found that the recruitment of the β-subunit isoform 1 of the Na(+)-K(+)-ATPase (β1NK) in NKCC2 MPCs was significantly increased in the kidneys of SHR compared with Wistar Kyoto rat control strain. Co-immunoprecipitation experiments showed that β1NK actually interacts with NKCC2 in the native tissue. The analysis of the physiological role of β1NK-NKCC2 interaction in human embryonic kidney cells showed that β1NK increased the steady-state membrane expression and activity of NKCC2 enhancing NKCC2 trafficking toward the plasma membrane. CONCLUSION We identify a new NKCC2-interacting partner involved in the modulation of NKCC2 intracellular trafficking and possibly involved in the regulation of blood pressure.
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Carmosino M, Gerbino A, Hendy GN, Torretta S, Rizzo F, Debellis L, Procino G, Svelto M. NKCC2 activity is inhibited by the Bartter's syndrome type 5 gain-of-function CaR-A843E mutant in renal cells. Biol Cell 2015; 107:98-110. [PMID: 25631355 DOI: 10.1111/boc.201400069] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 01/23/2015] [Indexed: 01/01/2023]
Abstract
BACKGROUND INFORMATION The gain-of-function A843E mutation of the calcium sensing receptor (CaR) causes Bartter syndrome type 5. Patients carrying this CaR variant show a remarkably reduced renal NaCl reabsorption in the thick ascending limb (TAL) of Henle's loop resulting in renal loss of NaCl in the absence of mutations in renal Na(+) and Cl(-) ion transporters. The molecular mechanisms underlying this clinical phenotype are incompletely understood. We investigated, in human embryonic kidney 293 (HEK 293) cells and porcine kidney epithelial (LLC-PK1) cells, the functional cross-talk of CaR-A843E with the Na(+):K(+):2Cl(-) co-transporter, NKCC2, which provides NaCl reabsorption in the TAL. RESULTS The expression of the CaR mutant did not alter the apical localisation of NKCC2 in LLC-PK1 cells. However, the steady-state NKCC2 phosphorylation and activity were decreased in cells transfected with CaR-A843E compared with the control wild-type CaR (CaR WT)-transfected cells. Of note, low-Cl(-)-dependent NKCC2 activation was also strongly inhibited upon the expression of CaR-A843E mutant. The use of either P450 ω-hydroxylase (CYP4)- or phospholipase A2 (PLA2)-blockers suggests that this effect is likely mediated by arachidonic acid (AA) metabolites. CONCLUSIONS The data suggested that the activated CaR affects intracellular pathways modulating NKCC2 activity rather than NKCC2 intracellular trafficking in renal cells, and throw further light on the pathological role played by active CaR mutants in Bartter syndrome type 5.
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Affiliation(s)
- Monica Carmosino
- Department of Biosciences, Biotechnologies, and Biopharmaceutics, University of Bari, 70125 Bari, Italy; Department of Sciences, University of Basilicata, 85100 Potenza, Italy
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Xue H, Zhang ZJ, Li XS, Sun HM, Kang Q, Wu B, Wang YX, Zou WJ, Zhou DS. Localization and vasopressin regulation of the Na +-K +-2Cl - cotransporter in the distal colonic epithelium. World J Gastroenterol 2014; 20:4692-4701. [PMID: 24782621 PMCID: PMC4000505 DOI: 10.3748/wjg.v20.i16.4692] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Revised: 02/09/2014] [Accepted: 03/05/2014] [Indexed: 02/06/2023] Open
Abstract
AIM: To investigate whether Na+-K+-2Cl- cotransporter (NKCC2) is expressed in the mouse distal colonic epithelia and whether it is regulated by vasopressin in the colon.
METHODS: The mRNA expression of NKCC2 in the mouse colonic mucosa was examined by reverse transcription-polymerase chain reaction. NKCC trafficking in the colon stimulated by 1-D-amino(8-D-arginine)-vasopressin (dDAVP) infusion (10 ng/mouse, intraperitoneal injection ) within 15 min, 30 min and 1h was investigated by laser confocal scanning microscopy. Total and membrane NKCC2 expression in the colonic mucosa from control and dDAVP-treated mice was detected by Western blotting. Short circuit current method was performed to determine regulation of NKCC2 by vasopressin in the colon.
RESULTS: NKCC2 was predominantly located in the apical region of the surface of the distal colonic epithelia; by comparison, a large amount of NKCC1 was distributed in the basolateral membrane of the lower crypt epithelia of the mouse distal colon. Short-term treatment with dDAVP, a V2-type receptor-specific vasopressin analog, induced NKCC2 re-distribution, i.e., NKCC2 traffics to the apical membrane after dDAVP stimulation. In contrast, no obvious NKCC1 membrane translocation was observed. Western blotting results confirmed that membrane NKCC2 had significantly higher abundance in the dDAVP-treated mouse colonic mucosa relative to that in the untreated control, which is consistent with our immunostaining data. Moreover, the short-circuit current method combined with a NKCC2 inhibitor demonstrated that NKCC2 was also activated by serosal vasopressin in isolated distal colonic mucosa.
CONCLUSION: Our results provide direct evidence that vasopressin also plays an important role in the colonic epithelia by stimulating NKCC2 trafficking to the apical membrane and inducing NKCC2-mediated ion transport.
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Carmosino M, Rizzo F, Torretta S, Procino G, Svelto M. High-throughput fluorescent-based NKCC functional assay in adherent epithelial cells. BMC Cell Biol 2013; 14:16. [PMID: 23506056 PMCID: PMC3618206 DOI: 10.1186/1471-2121-14-16] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Accepted: 02/28/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The kidney-specific NKCC cotransporter isoform NKCC2 is involved in the Na(+) reabsorption in the Thich Ascending Limb (TAL) cells and in the regulation of body fluid volume. In contrast, the isoform NKCC1 represents the major pathway for Cl- entry in endothelial cells, playing a crucial role in cell volume regulation and vascular tone. Importantly, both NKCC isoforms are involved in the regulation of blood pressure and represent important potential drug targets for the treatment of hypertension. RESULTS Taking advantage of an existing Thallium (Tl(+))-based kit, we set up a Tl(+) influx-based fluorescent assay, that can accurately and rapidly measure NKCC transporter activity in adherent epithelial cells using the high-throughput Flex station device. We assessed the feasibility of this assay in the renal epithelial LLC-PK1 cells stably transfected with a previously characterized chimeric NKCC2 construct (c-NKCC2). We demonstrated that the assay is highly reproducible, offers high temporal resolution of NKCC-mediated ion flux profiles and, importantly, being a continuous assay, it offers improved sensitivity over previous endpoint NKCC functional assays. CONCLUSIONS So far the screening of NKCC transporters activity has been done by (86)Rb(+) influx assays. Indeed, a fluorescence-based high-throughput screening method for testing NKCC inhibitors would be extremely useful in the development and characterization of new anti-hypertensive drugs.
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Affiliation(s)
- Monica Carmosino
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Via Amendola 165/A, Bari, 70126, Italy
- Department of Sciences, University of Basilicata, Via dell’Ateneo Lucano, Potenza, 85100, Italy
| | - Federica Rizzo
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Via Amendola 165/A, Bari, 70126, Italy
| | - Silvia Torretta
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Via Amendola 165/A, Bari, 70126, Italy
| | - Giuseppe Procino
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Via Amendola 165/A, Bari, 70126, Italy
| | - Maria Svelto
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Via Amendola 165/A, Bari, 70126, Italy
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