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Johnsen LØ, Friis KA, Møller-Madsen MK, Damkier HH. Mechanisms of cerebrospinal fluid secretion by the choroid plexus epithelium: Application to various intracranial pathologies. Clin Anat 2024. [PMID: 38894645 DOI: 10.1002/ca.24199] [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: 05/31/2024] [Revised: 06/02/2024] [Accepted: 06/06/2024] [Indexed: 06/21/2024]
Abstract
The choroid plexus (CP) is a small yet highly active epithelial tissue located in the ventricles of the brain. It secretes most of the CSF that envelops the brain and spinal cord. The epithelial cells of the CP have a high fluid secretion rate and differ from many other secretory epithelia in the organization of several key ion transporters. One striking difference is the luminal location of, for example, the vital Na+-K+-ATPase. In recent years, there has been a renewed focus on the role of ion transporters in CP secretion. Several studies have indicated that increased membrane transport activity is implicated in disorders such as hydrocephalus, idiopathic intracranial hypertension, and posthemorrhagic sequelae. The importance of the CP membrane transporters in regulating the composition of the CSF has also been a focus in research in recent years, particularly as a regulator of breathing and hemodynamic parameters such as blood pressure. This review focuses on the role of the fundamental ion transporters involved in CSF secretion and its ion composition. It gives a brief overview of the established factors and controversies concerning ion transporters, and finally discusses future perspectives related to the role of these transporters in the CP epithelium.
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2
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Solár P, Zamani A, Kubíčková L, Dubový P, Joukal M. Choroid plexus and the blood-cerebrospinal fluid barrier in disease. Fluids Barriers CNS 2020; 17:35. [PMID: 32375819 PMCID: PMC7201396 DOI: 10.1186/s12987-020-00196-2] [Citation(s) in RCA: 139] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Accepted: 04/22/2020] [Indexed: 01/08/2023] Open
Abstract
The choroid plexus (CP) forming the blood-cerebrospinal fluid (B-CSF) barrier is among the least studied structures of the central nervous system (CNS) despite its clinical importance. The CP is an epithelio-endothelial convolute comprising a highly vascularized stroma with fenestrated capillaries and a continuous lining of epithelial cells joined by apical tight junctions (TJs) that are crucial in forming the B-CSF barrier. Integrity of the CP is critical for maintaining brain homeostasis and B-CSF barrier permeability. Recent experimental and clinical research has uncovered the significance of the CP in the pathophysiology of various diseases affecting the CNS. The CP is involved in penetration of various pathogens into the CNS, as well as the development of neurodegenerative (e.g., Alzheimer´s disease) and autoimmune diseases (e.g., multiple sclerosis). Moreover, the CP was shown to be important for restoring brain homeostasis following stroke and trauma. In addition, new diagnostic methods and treatment of CP papilloma and carcinoma have recently been developed. This review describes and summarizes the current state of knowledge with regard to the roles of the CP and B-CSF barrier in the pathophysiology of various types of CNS diseases and sets up the foundation for further avenues of research.
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Affiliation(s)
- Peter Solár
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, CZ-625 00, Brno, Czech Republic
- Department of Neurosurgery, Faculty of Medicine, Masaryk University and St. Anne´s University Hospital Brno, Pekařská 53, CZ-656 91, Brno, Czech Republic
| | - Alemeh Zamani
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, CZ-625 00, Brno, Czech Republic
| | - Lucie Kubíčková
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, CZ-625 00, Brno, Czech Republic
| | - Petr Dubový
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, CZ-625 00, Brno, Czech Republic
| | - Marek Joukal
- Department of Anatomy, Cellular and Molecular Neurobiology Research Group, Faculty of Medicine, Masaryk University, CZ-625 00, Brno, Czech Republic.
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Cornejo I, Villanueva S, Burgos J, López-Cayuqueo KI, Chambrey R, Julio-Kalajzić F, Buelvas N, Niemeyer MI, Figueiras-Fierro D, Brown PD, Sepúlveda FV, Cid LP. Tissue Distribution of Kir7.1 Inwardly Rectifying K + Channel Probed in a Knock-in Mouse Expressing a Haemagglutinin-Tagged Protein. Front Physiol 2018; 9:428. [PMID: 29740340 PMCID: PMC5925607 DOI: 10.3389/fphys.2018.00428] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 04/05/2018] [Indexed: 11/13/2022] Open
Abstract
Kir7.1 encoded by the Kcnj13 gene in the mouse is an inwardly rectifying K+ channel present in epithelia where it shares membrane localization with the Na+/K+-pump. Further investigations of the localisation and function of Kir7.1 would benefit from the availability of a knockout mouse, but perinatal mortality attributed to cleft palate in the neonate has thwarted this research. To facilitate localisation studies we now use CRISPR/Cas9 technology to generate a knock-in mouse, the Kir7.1-HA that expresses the channel tagged with a haemagglutinin (HA) epitope. The availability of antibodies for the HA epitope allows for application of western blot and immunolocalisation methods using widely available anti-HA antibodies with WT tissues providing unambiguous negative control. We demonstrate that Kir7.1-HA cloned from the choroid plexus of the knock-in mouse has the electrophysiological properties of the native channel, including characteristically large Rb+ currents. These large Kir7.1-mediated currents are accompanied by abundant apical membrane Kir7.1-HA immunoreactivity. WT-controlled western blots demonstrate the presence of Kir7.1-HA in the eye and the choroid plexus, trachea and lung, and intestinal epithelium but exclusively in the ileum. In the kidney, and at variance with previous reports in the rat and guinea-pig, Kir7.1-HA is expressed in the inner medulla but not in the cortex or outer medulla. In isolated tubules immunoreactivity was associated with inner medulla collecting ducts but not thin limbs of the loop of Henle. Kir7.1-HA shows basolateral expression in the respiratory tract epithelium from trachea to bronchioli. The channel also appears basolateral in the epithelium of the nasal cavity and nasopharynx in newborn animals. We show that HA-tagged Kir7.1 channel introduced in the mouse by a knock-in procedure has functional properties similar to the native protein and the animal thus generated has clear advantages in localisation studies. It might therefore become a useful tool to unravel Kir7.1 function in the different organs where it is expressed.
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Affiliation(s)
| | - Sandra Villanueva
- Centro de Estudios Científicos, Valdivia, Chile.,Universidad Austral de Chile, Valdivia, Chile
| | - Johanna Burgos
- Centro de Estudios Científicos, Valdivia, Chile.,Universidad Austral de Chile, Valdivia, Chile
| | - Karen I López-Cayuqueo
- Centro de Estudios Científicos, Valdivia, Chile.,Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche S970, PARCC, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France
| | - Régine Chambrey
- Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche S970, PARCC, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France
| | | | | | | | | | - Peter D Brown
- School of Medical Sciences, University of Manchester, Manchester, United Kingdom
| | | | - L P Cid
- Centro de Estudios Científicos, Valdivia, Chile
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4
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Christensen HL, Păunescu TG, Matchkov V, Barbuskaite D, Brown D, Damkier HH, Praetorius J. The V-ATPase is expressed in the choroid plexus and mediates cAMP-induced intracellular pH alterations. Physiol Rep 2017; 5:5/1/e13072. [PMID: 28053225 PMCID: PMC5256157 DOI: 10.14814/phy2.13072] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Revised: 11/16/2016] [Accepted: 11/18/2016] [Indexed: 11/24/2022] Open
Abstract
The cerebrospinal fluid (CSF) pH influences brain interstitial pH and, therefore, brain function. We hypothesized that the choroid plexus epithelium (CPE) expresses the vacuolar H+‐ATPase (V‐ATPase) as an acid extrusion mechanism in the luminal membrane to counteract detrimental elevations in CSF pH. The expression of mRNA corresponding to several V‐ATPase subunits was demonstrated by RT‐PCR analysis of CPE cells (CPECs) isolated by fluorescence‐activated cell sorting. Immunofluorescence and electron microscopy localized the V‐ATPase primarily in intracellular vesicles with only a minor fraction in the luminal microvillus area. The vesicles did not translocate to the luminal membrane in two in vivo models of hypocapnia‐induced alkalosis. The Na+‐independent intracellular pH (pHi) recovery from acidification was studied in freshly isolated clusters of CPECs. At extracellular pH (pHo) 7.4, the cells failed to display significant concanamycin A‐sensitive pHi recovery (i.e., V‐ATPase activity). The recovery rate in the absence of Na+ amounted to <10% of the pHi recovery rate observed in the presence of Na+. Recovery of pHi was faster at pHo 7.8 and was abolished at pHo 7.0. The concanamycin A‐sensitive pHi recovery was stimulated by cAMP at pH 7.4 in vitro, but intraventricular infusion of the membrane‐permeant cAMP analog 8‐CPT‐cAMP did not result in trafficking of the V‐ATPase. In conclusion, we find evidence for the expression of a minor fraction of V‐ATPase in the luminal membrane of CPECs. This fraction does not contribute to enhanced acid extrusion at high extracellular pH, but seems to be activated by cAMP in a trafficking‐independent manner.
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Affiliation(s)
| | - Teodor G Păunescu
- Center for Systems Biology, Program in Membrane Biology/Nephrology Division, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
| | - Vladimir Matchkov
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark
| | - Dagne Barbuskaite
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences University of Copenhagen, Copenhagen, Denmark
| | - Dennis Brown
- Center for Systems Biology, Program in Membrane Biology/Nephrology Division, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
| | - Helle H Damkier
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences University of Copenhagen, Copenhagen, Denmark
| | - Jeppe Praetorius
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark
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5
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Praetorius J, Damkier HH. Transport across the choroid plexus epithelium. Am J Physiol Cell Physiol 2017; 312:C673-C686. [PMID: 28330845 DOI: 10.1152/ajpcell.00041.2017] [Citation(s) in RCA: 74] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 03/17/2017] [Accepted: 03/17/2017] [Indexed: 11/22/2022]
Abstract
The choroid plexus epithelium is a secretory epithelium par excellence. However, this is perhaps not the most prominent reason for the massive interest in this modest-sized tissue residing inside the brain ventricles. Most likely, the dominant reason for extensive studies of the choroid plexus is the identification of this epithelium as the source of the majority of intraventricular cerebrospinal fluid. This finding has direct relevance for studies of diseases and conditions with deranged central fluid volume or ionic balance. While the concept is supported by the vast majority of the literature, the implication of the choroid plexus in secretion of the cerebrospinal fluid was recently challenged once again. Three newer and promising areas of current choroid plexus-related investigations are as follows: 1) the choroid plexus epithelium as the source of mediators necessary for central nervous system development, 2) the choroid plexus as a route for microorganisms and immune cells into the central nervous system, and 3) the choroid plexus as a potential route for drug delivery into the central nervous system, bypassing the blood-brain barrier. Thus, the purpose of this review is to highlight current active areas of research in the choroid plexus physiology and a few matters of continuous controversy.
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Affiliation(s)
- Jeppe Praetorius
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark; and
| | - Helle Hasager Damkier
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark; and.,Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Abstract
KCNE2, originally designated MinK-related peptide 1 (MiRP1), belongs to a five-strong family of potassium channel ancillary (β) subunits that, despite the diminutive size of the family and its members, has loomed large in the field of ion channel physiology. KCNE2 dictates K (+) channel gating, conductance, α subunit composition, trafficking and pharmacology, and also modifies functional properties of monovalent cation-nonselective HCN channels. The Kcne2 (-/-) mouse exhibits cardiac arrhythmia and hypertrophy, achlorhydria, gastric neoplasia, hypothyroidism, alopecia, stunted growth and choroid plexus epithelial dysfunction, illustrating the breadth and depth of the influence of KCNE2, mutations which are also associated with human cardiac arrhythmias. Here, the modus operandi and physiological roles of this potent regulator of membrane excitability and ion secretion are reviewed with particular emphasis on the ability of KCNE2 to shape the electrophysiological landscape of both excitable and non-excitable cells.
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Affiliation(s)
- Geoffrey W Abbott
- Departments of Pharmacology and Physiology and Biophysics, University of California, Irvine, Irvine, CA, USA.
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7
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Damkier HH, Brown PD, Praetorius J. Epithelial pathways in choroid plexus electrolyte transport. Physiology (Bethesda) 2010; 25:239-49. [PMID: 20699470 DOI: 10.1152/physiol.00011.2010] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A stable intraventricular milieu is crucial for maintaining normal neuronal function. The choroid plexus epithelium produces the cerebrospinal fluid and in doing so influences the chemical composition of the interstitial fluid of the brain. Here, we review the molecular pathways involved in transport of the electrolytes Na+, K+, Cl-, and HCO3(-)across the choroid plexus epithelium.
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Affiliation(s)
- Helle H Damkier
- Department of Anatomy and the Water and Salt Research Center, Aarhus University, Aarhus C, Denmark
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Abstract
The choroid plexus is a specialized tissue that lines subdomains within the four ventricles of the brain where most of the cerebrospinal fluid is produced. Maintenance of an equilibrium in volume and composition of the cerebrospinal fluid (CSF) is vital for a normal brain function, ensuring an optimal environment for the neurons. The necessarily high water permeability of the choroid plexus barrier is made possible by the abundant expression of a water channel, Aquaporin-1 (AQP1), on the apical side of the membrane from early stages of development through adulthood. Data from studies of AQP1 suggest that it also can contribute as a gated ion channel, and suggest that the AQP1-mediated ionic conductance has physiological significance for the regulation of cerebrospinal fluid secretion. The regulation of AQP1 ion channels could be one of several transport mechanisms that contribute to the decreased CSF secretion in response to endogenous signaling molecules such as atrial natriuretic peptide. Numerous classes of ion channels and transporters are targeted specifically to each side of the cellular membrane, and they all work in concert to secrete CSF. Several signaling cascades have a direct effect on transporters and ion channels present in the choroid plexus epithelium, altering their transport activity and therefore modulating the net transcellular movement of solutes and water. Several neurotransmitters, neuropeptides, and growth factors can influence CSF secretion by direct effect on transport mechanisms of the epithelium. The mammalian choroid plexus receives innervation from noradrenergic sympathetic fibers, cholinergic and peptidergic fibers that modulate CSF secretion. Water imbalance in the brain can have life-threatening consequences resulting from altered excitability and neurodegeneration, disruption of the supply of nutrients, loss of signaling molecules, and the accumulation of unwanted toxins and metabolites. Understanding the mechanisms involved in the modulation of CSF secretion is of fundamental importance. An appreciation of AQP1 as an ion channel in addition to its role as a water channel should offer new targets for therapeutic strategies in diseases involving water imbalance in the brain.
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Affiliation(s)
- Daniela Boassa
- Department of Physiology, University of Arizona College of Medicine, Tucson, Arizona 85724, USA
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Millar ID, Bruce JIE, Brown PD. Ion channel diversity, channel expression and function in the choroid plexuses. Cerebrospinal Fluid Res 2007; 4:8. [PMID: 17883837 PMCID: PMC2072944 DOI: 10.1186/1743-8454-4-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Accepted: 09/20/2007] [Indexed: 12/11/2022] Open
Abstract
Knowledge of the diversity of ion channel form and function has increased enormously over the last 25 years. The initial impetus in channel discovery came with the introduction of the patch clamp method in 1981. Functional data from patch clamp experiments have subsequently been augmented by molecular studies which have determined channel structures. Thus the introduction of patch clamp methods to study ion channel expression in the choroid plexus represents an important step forward in our knowledge understanding of the process of CSF secretion. Two K+ conductances have been identified in the choroid plexus: Kv1 channel subunits mediate outward currents at depolarising potentials; Kir 7.1 carries an inward-rectifying conductance at hyperpolarising potentials. Both K+ channels are localised at the apical membrane where they may contribute to maintenance of the membrane potential while allowing the recycling of K+ pumped in by Na+-K+ ATPase. Two anion conductances have been identified in choroid plexus. Both have significant HCO3- permeability, and may play a role in CSF secretion. One conductance exhibits inward-rectification and is regulated by cyclic AMP. The other is carried by an outward-rectifying channel, which is activated by increases in cell volume. The molecular identity of the anion channels is not known, nor is it clear whether they are expressed in the apical or basolateral membrane. Recent molecular evidence indicates that choroid plexus also expresses the non-selective cation channels such as transient receptor potential channels (TRPV4 and TRPM3) and purinoceptor type 2 (P2X) receptor operated channels. In conclusion, good progress has been made in identifying the channels expressed in the choroid plexus, but determining the precise roles of these channels in CSF secretion remains a challenge for the future.
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Affiliation(s)
- Ian D Millar
- Faculty of Life Sciences, Core Technology Facility, University of Manchester, Manchester M13 9NT, UK
| | - Jason IE Bruce
- Faculty of Life Sciences, Core Technology Facility, University of Manchester, Manchester M13 9NT, UK
| | - Peter D Brown
- Faculty of Life Sciences, Core Technology Facility, University of Manchester, Manchester M13 9NT, UK
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10
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Praetorius J. Water and solute secretion by the choroid plexus. Pflugers Arch 2006; 454:1-18. [PMID: 17120021 DOI: 10.1007/s00424-006-0170-6] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Accepted: 09/12/2006] [Indexed: 12/23/2022]
Abstract
The cerebrospinal fluid (CSF) provides mechanical and chemical protection of the brain and spinal cord. This review focusses on the contribution of the choroid plexus epithelium to the water and salt homeostasis of the CSF, i.e. the secretory processes involved in CSF formation. The choroid plexus epithelium is situated in the ventricular system and is believed to be the major site of CSF production. Numerous studies have identified transport processes involved in this secretion, and recently, the underlying molecular background for some of the mechanisms have emerged. The nascent CSF consists mainly of NaCl and NaHCO(3), and the production rate is strictly coupled to the rate of Na(+) secretion. In contrast to other secreting epithelia, Na(+) is actively pumped across the luminal surface by the Na(+),K(+)-ATPase with possible contributions by other Na(+) transporters, e.g. the luminal Na(+),K(+),2Cl(-) cotransporter. The Cl(-) and HCO(3) (-) ions are likely transported by a luminal cAMP activated inward rectified anion conductance, although the responsible proteins have not been identified. Whereas Cl(-) most likely enters the cells through anion exchange, the functional as well as the molecular basis for the basolateral Na(+) entry are not yet well-defined. Water molecules follow across the epithelium mainly through the water channel, AQP1, driven by the created ionic gradient. In this article, the implications of the recent findings for the current model of CSF secretion are discussed. Finally, the clinical implications and the prospects of future advances in understanding CSF production are briefly outlined.
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Affiliation(s)
- Jeppe Praetorius
- The Water and Salt Research Center & Institute of Anatomy, University of Aarhus, Wilhelm Meyers Allé, 8000 Aarhus, Denmark.
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11
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Brown PD, Davies SL, Speake T, Millar ID. Molecular mechanisms of cerebrospinal fluid production. Neuroscience 2005; 129:957-70. [PMID: 15561411 PMCID: PMC1890044 DOI: 10.1016/j.neuroscience.2004.07.003] [Citation(s) in RCA: 287] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/02/2004] [Indexed: 11/23/2022]
Abstract
The epithelial cells of the choroid plexuses secrete cerebrospinal fluid (CSF), by a process which involves the transport of Na(+), Cl(-) and HCO(3)(-) from the blood to the ventricles of the brain. The unidirectional transport of ions is achieved due to the polarity of the epithelium, i.e. the ion transport proteins in the blood-facing (basolateral) membrane are different to those in the ventricular (apical) membrane. The movement of ions creates an osmotic gradient which drives the secretion of H(2)O. A variety of methods (e.g. isotope flux studies, electrophysiological, RT-PCR, in situ hybridization and immunocytochemistry) have been used to determine the expression of ion transporters and channels in the choroid plexus epithelium. Most of these transporters have now been localized to specific membranes. For example, Na(+)-K(+)ATPase, K(+) channels and Na(+)-2Cl(-)-K(+) cotransporters are expressed in the apical membrane. By contrast the basolateral membrane contains Cl(-)- HCO(3) exchangers, a variety of Na(+) coupled HCO(3)(-) transporters and K(+)-Cl(-) cotransporters. Aquaporin 1 mediates water transport at the apical membrane, but the route across the basolateral membrane is unknown. A model of CSF secretion by the mammalian choroid plexus is proposed which accommodates these proteins. The model also explains the mechanisms by which K(+) is transported from the CSF to the blood.
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Affiliation(s)
- P D Brown
- School of Biological Sciences, G.38 Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK.
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12
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Escobar LI, Martínez-Téllez JC, Salas M, Castilla SA, Carrisoza R, Tapia D, Vázquez M, Bargas J, Bolívar JJ. A voltage-gated K+ current in renal inner medullary collecting duct cells. Am J Physiol Cell Physiol 2004; 286:C965-74. [PMID: 14684382 DOI: 10.1152/ajpcell.00074.2003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We studied the K+-selective conductances in primary cultures of rat renal inner medullary collecting duct (IMCD) using perforated-patch and conventional whole cell techniques. Depolarizations above –20 mV induced a time-dependent outward K+ current ( Ivto) similar to a delayed rectifier. Ivto showed a half-maximal activation around 5.6 mV with a slope factor of 6.8 mV. Its K+/Na+ selectivity ratio was 11.7. It was inhibited by tetraethylammonium, quinidine, 4-aminopyridine, and Ba2+ and was not Ca2+ dependent. The delayed rectifying characteristics of Ivto prompted us to screen the expression of Kv1 and Kv3 families by RT-PCR. Analysis of RNA isolated from cell cultures revealed the presence of three Kv α-subunits (Kv1.1, Kv1.3, and Kv1.6). Western blot analysis with Kv α-subunit antibodies for Kv1.1 and Kv1.3 showed labeling of ∼70-kDa proteins from inner medulla plasmatic and microsome membranes. Immunocytochemical analysis of cell culture and kidney inner medulla showed that Kv1.3 is colocalized with the Na+-K+-ATPase at the basolateral membrane, although it is also in the cytoplasm. This is the first evidence of recording, protein expression, and localization of a voltage-gated Kv1 in the kidney IMCD cells.
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Affiliation(s)
- Laura I Escobar
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, México City DF, 04510, México.
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13
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Speake T, Brown PD. Ion channels in epithelial cells of the choroid plexus isolated from the lateral ventricle of rat brain. Brain Res 2004; 1005:60-6. [PMID: 15044065 DOI: 10.1016/j.brainres.2004.01.034] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/28/2004] [Indexed: 10/26/2022]
Abstract
Whole-cell patch clamp methods were used to determine the expression of ion channels in the epithelial cells of choroid plexus isolated from the lateral ventricle of the rat brain. A single population of cells with a mean capacitance of 61.5+/-1.7 pF was identified in 103 recordings. This value is significantly greater than that measured for cells from the fourth ventricle (P<0.01 by unpaired t-test), indicating that cells from the lateral ventricle have a greater surface area. Voltage-dependent, outward currents were recorded using a K(+)-rich electrode solution. These currents were partially inhibited by 10 nM margatoxin or 10 nM dendrotoxin-K and blocked by 5 mM TEA(+). An inward-rectifying chloride conductance was observed in K(+)-free solutions. The relative permeability of this conductance to anions was P(I)>P(Cl)>P(aspartate). A volume-sensitive anion conductance was observed when cell swelling was induced using a hypertonic electrode solution. The properties of each conductance were similar to conductances previously identified in fourth ventricle choroid plexus cells. Furthermore, there were no significant differences between the magnitudes of any of the conductances in cells from the lateral and fourth ventricle choroid plexus. Thus, the ionic conductances expressed in rat lateral and fourth ventricle choroid plexus are very similar.
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Affiliation(s)
- Tracey Speake
- School of Biological Sciences, University of Manchester, G.38 Stopford Building, Manchester Ml3 9PT, UK
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14
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Speake T, Kibble JD, Brown PD. Kv1.1 and Kv1.3 channels contribute to the delayed-rectifying K+conductance in rat choroid plexus epithelial cells. Am J Physiol Cell Physiol 2004; 286:C611-20. [PMID: 14602579 DOI: 10.1152/ajpcell.00292.2003] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The choroid plexuses secrete, and maintain the composition of, the cerebrospinal fluid. K+channels play an important role in these processes. In this study the molecular identity and properties of the delayed-rectifying K+(Kv) conductance in rat choroid plexus epithelial cells were investigated. Whole cell K+currents were significantly reduced by 10 nM dendrotoxin-K and 1 nM margatoxin, which are specific inhibitors of Kv1.1 and Kv1.3 channels, respectively. A combination of dendrotoxin-K and margatoxin caused a depolarization of the membrane potential in current-clamp experiments. Western blot analysis indicated the presence of Kv1.1 and Kv1.3 proteins in the choroid plexus. Furthermore, the Kv1.3 and Kv1.1 proteins appear to be expressed in the apical membrane of the epithelial cells in immunocytochemical studies. The Kv conductance was inhibited by 1 μM serotonin (5-HT), with maximum inhibition to 48% of control occurring in 8 min ( P < 0.05 by Student's t-test for paired data). Channel inhibition by 5-HT was prevented by the 5-HT2Cantagonist mesulergine (300 nM). It was also attenuated in the presence of calphostin C (a protein kinase C inhibitor). The conductance was partially inhibited by 1,2-dioctanoyl- sn-glycerol and phorbol 12-myristate 13-acetate, both of which activate protein kinase C. These data suggest that 5-HT acts at 5-HT2Creceptors to activate protein kinase C, which inhibits the Kv channels. In conclusion, Kv1.1 and Kv1.3 channels make a significant contribution to K+efflux at the apical membrane of the choroid plexus.
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Affiliation(s)
- Tracey Speake
- School of Biological Sciences, University of Manchester, Manchester M13 9PT, United Kingdom
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15
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Speake T, Kajita H, Smith CP, Brown PD. Inward-rectifying anion channels are expressed in the epithelial cells of choroid plexus isolated from ClC-2 'knock-out' mice. J Physiol 2002; 539:385-90. [PMID: 11882672 PMCID: PMC2290149 DOI: 10.1113/jphysiol.2001.014548] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Choroid plexus epithelial cells express inward-rectifying anion channels which have a high HCO(3)(-) permeability. These channels are thought to have an important role in the secretion of cerebrospinal fluid. The possible relationship between these channels and the ClC-2 Cl(-) channel was investigated in the present study. RT-PCR, using specific ClC-2 primers, amplified a 238 bp fragment of mRNA from rat choroid plexus, which was 99 % identical to the 5' sequence of rat ClC-2. A 2005 bp clone was isolated from a rat choroid plexus cDNA library using a probe for ClC-2. The clone showed greater than 99 % identity with the sequence of rat ClC-2. Inward-rectifying anion channels were observed in whole-cell recordings of choroid plexus epithelial cells isolated from ClC-2 knock-out mice. The mean inward conductance was 19.6 plus minus 3.6 nS (n = 8) in controls (3 heterozygote animals), and 22.5 plus minus 3.1 nS (n = 10) in three knock-out animals. The relative permeability of the conductances to I(-) and Cl(-) (P(I) : P(Cl)) was determined. I(-) was more permeant than Cl(-) in both heterozygotes (P(I):P(Cl) = 4.0 +/- 0.9, n = 3) and knock-out animals (P(I) : P(Cl) = 4.1 +/- 1.4, n = 3). These results indicate that rat choroid plexus expresses the ClC-2 variant that was originally reported in other tissues. ClC-2 does not contribute significantly to inward-rectifying anion conductance in mouse choroid plexus, which must therefore express a novel inward-rectifying anion channel.
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Affiliation(s)
- Tracey Speake
- School of Biological Sciences, University of Manchester, Manchester M13 9PT, UK
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16
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Abstract
The epithelial cells of the choroid plexus secrete cerebrospinal fluid (CSF), by a process that involves the movement of Na(+), Cl(-) and HCO(3)(-) from the blood to the ventricles of the brain. This creates the osmotic gradient, which drives the secretion of H(2)O. The unidirectional movement of the ions is achieved due to the polarity of the epithelium, i.e., the ion transport proteins in the blood-facing (basolateral) are different to those in the ventricular (apical) membranes. Saito and Wright (1983) proposed a model for secretion by the amphibian choroid plexus, in which secretion was dependent on activity of HCO(3)(-) channels in the apical membrane. The patch clamp method has now been used to study the ion channels expressed in rat choroid plexus. Two potassium channels have been observed that have a role in maintaining the membrane potential of the epithelial cell, and in regulating the transport of K(+) across the epithelium. An inward-rectifying anion channel has also been identified, which is closely related to ClC-2 channels, and has a significant HCO(3)(-) permeability. This channel is expressed in the apical membrane of the epithelium where it may play an important role in CSF secretion. A model of CSF secretion by the mammalian choroid plexus is proposed that accommodates these channels and other data on the expression of transport proteins in the choroid plexus.
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Affiliation(s)
- T Speake
- School of Biological Sciences, University of Manchester, Manchester M13 9PT, United Kingdom
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17
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Abstract
A brief outline is given first of the early history of the ventricles and the strange ideas of their functions from Galen to the enlightenment of the Renaissance with the work of Versalius. This is followed by a description of the histology of the choroid plexuses (CP) and discussion on the functions of the choroid plexus and on the composition of cerebrospinal fluid (CSF). The methods of measuring the rate of secretion of CSF will be outlined and the possible nutritive functions of the choroid plexuses will be considered. The role of the choroid plexuses in the control of the concentration of glucose and amino acids in CSF will be compared with data from in vitro experiments to that from the isolated vascularly perfused choroid plexuses. The handling of peptides and proteins by the CP and the synthesis of these molecules by this tissue is then discussed and the effects of lead on the synthesis of transthyretin by this tissue. Finally, reference will be made to the extensive neuro-endocrine role of the CP and efflux systems across the tissue for lipid soluble molecules.
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Affiliation(s)
- M B Segal
- Guy's, King's and St. Thomas' School of Biomedical Sciences, King's College London, St. Thomas' Hospital, London SE1 7EH, United Kingdom.
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18
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Battle T, Preisser L, Marteau V, Meduri G, Lambert M, Nitschke R, Brown PD, Corman B. Vasopressin V1a receptor signaling in a rat choroid plexus cell line. Biochem Biophys Res Commun 2000; 275:322-7. [PMID: 10964665 DOI: 10.1006/bbrc.2000.3301] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
A new cell line was derived from primary culture of rat choroid plexus (RCP) by immortalization with the TSOri minus adenovirus. The selected clone expressed vasopressin V1a receptors at a density of 64,000 sites per cell, and a K(d) of 7.2 nM. Addition of vasopressin to the RCP cells induced a transient calcium peak comparable to V1a receptor signalling in different expression systems. This [Ca(2+)](i) increase was dose-dependent with an EC(50) of 22 nM vasopressin. Similar [Ca(2+)](i) increase was elicited by addition of serotonin, angiotensin II, endothelin-1, and bradykinin. Heterologous desensitization of V1a receptor was observed in RCP cells exposed to the phorbol ester PMA or following stimulation of other receptors coupled to the phosphoinositide pathway. Positive immunolabelling with Factor VIII, Flt1 and CD 34 antibodies suggests that this new RCP cell line originated from endothelial cells of rat choroid plexus.
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Affiliation(s)
- T Battle
- C.A.M.R., Salisbury, United Kingdom
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19
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Kindler CH, Pietruck C, Yost CS, Sampson ER, Gray AT. Localization of the tandem pore domain K+ channel TASK-1 in the rat central nervous system. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2000; 80:99-108. [PMID: 11039733 DOI: 10.1016/s0169-328x(00)00136-4] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Recently, a new family of potassium channels with two pore domains in tandem and four transmembrane segments has been identified. Seven functional mammalian channels have been reported at this time. These channels give rise to baseline potassium currents because they are not gated by voltage and exhibit spontaneous activity at all membrane potentials. Although the physiological role of these ion channels has yet to be determined, three mammalian members of this family (TREK-1, TASK-1, TASK-2) are activated by volatile anesthetics and may therefore contribute to the central nervous system (CNS) depression produced by volatile anesthetics. In this study we used northern blot analysis and immunohistochemical localization to determine the expression of TASK-1 subunits in the CNS. TASK-1 immunoreactivity was prominently found in astrocytes of the hippocampus, in the median eminence, in the choroid plexus, and the granular layer, Purkinje cell layer, and molecular layer of the cerebellum. In the spinal cord, strong TASK-I immunoreactivity was seen in ependymal cells lining the central canal and in white matter. These findings suggest a role for the TASK-1 channel in the production of cerebrospinal fluid and function of hypothalamic neurosecretory cells.
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Affiliation(s)
- C H Kindler
- Department of Anesthesia, University of Basel, Kantonsspital, Switzerland.
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20
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Segal MB. The choroid plexuses and the barriers between the blood and the cerebrospinal fluid. Cell Mol Neurobiol 2000; 20:183-96. [PMID: 10696509 DOI: 10.1023/a:1007045605751] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
1. The fluid homeostasis of the brain depends both on the endothelial blood-brain barrier and on the epithelial blood-cerebrospinal fluid (CSF) barrier located at the choroid plexuses and the outer arachnoid membrane. 2. The brain has two fluid environments: the brain interstitial fluid, which surrounds the neurons and glia, and the CSF, which fills the ventricles and external surfaces of the central nervous system. 3. CSF acts as a fluid cushion for the brain and as a drainage route for the waste products of cerebral metabolism. 4. Recent findings suggest that CSF may also act as a "third circulation" conveying substances secreted into the CSF rapidly to many brain regions.
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Affiliation(s)
- M B Segal
- Division of Physiology, Guy's, King's and St. Thomas' School of Biomedical Sciences, King's College London, UK.
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21
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Abstract
Rat and human cDNAs were isolated that both encoded a 360 amino acid polypeptide with a tertiary structure typical of inwardly rectifying K+ channel (Kir) subunits. The new proteins, termed Kir7.1, were <37% identical to other Kir subunits and showed various unique residues at conserved sites, particularly near the pore region. High levels of Kir7.1 transcripts were detected in rat brain, lung, kidney, and testis. In situ hybridization of rat brain sections demonstrated that Kir7.1 mRNA was absent from neurons and glia but strongly expressed in the secretory epithelial cells of the choroid plexus (as confirmed by in situ patch-clamp measurements). In cRNA-injected Xenopus oocytes Kir7.1 generated macroscopic Kir currents that showed a very shallow dependence on external K+ ([K+]e), which is in marked contrast to all other Kir channels. At a holding potential of -100 mV, the inward current through Kir7.1 averaged -3.8 +/- 1.04 microA with 2 mM [K+]e and -4.82 +/- 1.87 microA with 96 mM [K+]e. Kir7.1 has a methionine at position 125 in the pore region where other Kir channels have an arginine. When this residue was replaced by the conserved arginine in mutant Kir7.1 channels, the pronounced dependence of K+ permeability on [K+]e, characteristic for other Kir channels, was restored and the Ba2+ sensitivity was increased by a factor of approximately 25 (Ki = 27 microM). These findings support the important role of this site in the regulation of K+ permeability in Kir channels by extracellular cations.
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22
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Takeuchi S, Ando M. Inwardly rectifying K+ currents in intermediate cells in the cochlea of gerbils: a possible contribution to the endocochlear potential. Neurosci Lett 1998; 247:175-8. [PMID: 9655621 DOI: 10.1016/s0304-3940(98)00318-8] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The stria vascularis in the cochlea generates the endocochlear potential (EP) and secretes K+-rich endolymph; both are indispensable for normal sound transduction by hair cells. K+ conductance in the intermediate cell, one of the several types of cells constituting the stria vascularis, was investigated by the whole-cell patch-clamp technique. Inwardly-rectifying K+ (Kir) currents were the major currents observed. The currents were inhibited dose-dependently by Ba2+, quinine, verapamil and Cs+, but not by tetraethylammonium (20 mM), 4-aminopyridine (5 mM) or Cd2+ (1 mM). The similarity between the effect of inhibitors on Kir currents and on the EP (Takeuchi et al., Hearing Res., 101 (1996) 181-185) suggests a direct contribution of the Kir conductance to the generation of the EP.
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Affiliation(s)
- S Takeuchi
- Department of Physiology, Kochi Medical School, Nankoku, Japan.
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23
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Dickinson KE, Baska RA, Cohen RB, Bryson CC, Smith MA, Schroeder K, Lodge NJ. Identification of [3H]P1075 binding sites and P1075-activated K+ currents in ovine choroid plexus cells. Eur J Pharmacol 1998; 345:97-101. [PMID: 9593600 DOI: 10.1016/s0014-2999(97)01617-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
This study examined the pharmacological characteristics of binding sites for the potent K+ channel opener [3H]P1075, as well as the functional effects of P1075 on ionic currents and membrane potential, in ovine choroid plexus (OCP) cells. [3H]P1075 bound to OCP cells with a Kd of 26 +/- 4 nM and a Bmax of 10400 +/- 480 sites/cell. Labelled sites were stereoselective and inhibited by potassium channel openers with a rank order of potency: P1075 > BMS-182264, ((4-[[9cyanoimino)[(1,2,2-trimethylpropyl)amino]-methyl]amino]benz onitrile) > pinacidil >> nicorandil > diazoxide. The K(ATP) channel antagonist glyburide inhibited [3H]P1075 binding with a Ki of 2 microM. The presence of K(ATP) channels on OCP cells was examined by patch clamp and fluorescent (membrane-potential sensitive dye) techniques. In some cells, P1075 activated an outward potassium current which was blocked by glyburide. P1075 produced a glyburide-sensitive, concentration-dependent, hyperpolarization of OCP cells. Levcromakalim hyperpolarized more strongly than its 3R,4S enantiomer, BRL 38226 ((3R-trans)-3,4-dihydro-3-hydroxy-2,2-dimethyl-4-(2-oxo-1-pyrrolidinyl)- 2H-1-benzopyran-6-carbonitrile) indicating a stereoselective interaction. These data indicate that epithelial OCP cells contain glyburide-sensitive K(ATP) channels.
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Affiliation(s)
- K E Dickinson
- Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, NJ 08543-4000, USA
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24
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Takahira M, Hughes BA. Isolated bovine retinal pigment epithelial cells express delayed rectifier type and M-type K+ currents. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C790-803. [PMID: 9316397 DOI: 10.1152/ajpcell.1997.273.3.c790] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Outwardly rectifying K+ currents in freshly isolated bovine retinal pigment epithelial (RPE) cells were characterized using the whole cell and perforated-patch configurations of the patch-clamp technique. All cells exhibited a delayed rectifier type K+ current. This current had an activation threshold voltage of approximately -40 mV, activated with a sigmoidal trajectory, and inactivated completely over a period of several seconds. External tetraethylammonium (TEA) was an effective blocker of the delayed rectifier current [apparent dissociation constant (Kd) = 5.1 mM], but external Ba2+ was relatively ineffective. Approximately 24% of the cells also exhibited a sustained outwardly rectifying K+ current that became activated at voltages positive to approximately -80 mV. This current resembled the neuronal M-current. External Ba2+ was a potent blocker of this current (apparent Kd = 1.1 mM), but external TEA and Cs+ were relatively ineffective. These results indicate that freshly isolated bovine RPE cells express K+ currents of both the delayed rectifier and M types. The latter may contribute to the resting K+ conductances of the apical and basolateral membranes.
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Affiliation(s)
- M Takahira
- Department of Ophthalmology, University of Michigan, Ann Arbor 48105, USA
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25
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Kajita H, Brown PD. Inhibition of the inward-rectifying Cl- channel in rat choroid plexus by a decrease in extracellular pH. J Physiol 1997; 498 ( Pt 3):703-7. [PMID: 9051581 PMCID: PMC1159186 DOI: 10.1113/jphysiol.1997.sp021894] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. The sensitivity of the inward-rectifying Cl- channel in choroid plexus to changes in external pH (pHo) was examined. 2. Cl- currents were recorded using whole-cell patch-clamp methods. The inward-rectifying channel was activated by 375 nM of the catalytic subunit of protein kinase A which was added to the electrode solution. 3. Reducing pHo from 7.3 to 6.5 inhibited the inward-rectifying Cl- currents, whereas an increase in current was observed when pHo was elevated to 8.5. The inhibition of the conductance exhibited a sigmoidal relationship with decreasing pH over a range of 8.5 to 5.5. A half-maximal inhibition of the current was observed at pH 7.3. 4. The inhibition of the whole-cell current by reducing pHo suggests that it is carried by channels which are distinct from other inward-rectifier Cl- channels, e.g. ClC-2, phospholemman and the channel in Xenopus oocytes.
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Affiliation(s)
- H Kajita
- Cell Physiology Group, School of Biological Sciences, University of Manchester, UK
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26
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Wu D, Mori N. Outward K+ current in epithelial cells isolated from intermediate portion of endolymphatic sac of guinea pigs. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 271:C1765-73. [PMID: 8944662 DOI: 10.1152/ajpcell.1996.271.5.c1765] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Ion currents in epithelial cells isolated from the intermediate portion of endolymphatic sac (ES) in guinea pigs were investigated with the use of the whole cell patch-clamp technique. Depolarizing voltage steps from a holding potential of -60 mV induced a time- and voltage-dependent outward current, which is comparable to that of delayed rectifying K+ currents. The average resting membrane potential in the current-clamp mode was -54.8 +/- 11 mV (n = 45), which was similar to the value of zero current potential (-55.6 +/- 0.8 mV, n = 32) obtained from current-voltage (I-V) relationships of outward currents in voltage-clamp mode. The I-V relationship of the tail current exhibited a reversal potential (Erev) of -78.1 +/- 0.9 mV (n = 19) in standard external solution. The Erev of the outward current was linearly related to the logarithm of extracellular K+ concentrations. The slope was 48 mV per 10-fold change in extracellular K+ concentrations. The time constants of K+ current activation, inactivation, and K+ tail current deactivation were voltage dependent. The steady-state activation and inactivation of K+ current exhibited a sigmoidal relationship to voltage. The 50% maximal activation voltage and slope factor were -21 and 11 mV (n = 8), respectively. The 50% maximal inactivation voltage and slope factor were -45 and 13 mV (n = 7), respectively. The K+ current was blocked by externally applied 1 mM 4-aminopyridine (4-AP), 5 mM Ba2+ and 20 mM tetraethylammonium chloride (TEA). The sensitivity of the current to 4-AP and Ba2+ was higher than that to TEA. Elimination of external Ca2+ and increase of internal Ca2+ failed to significantly change the current, suggesting that the K+ current may be Ca2+ independent. The results show that epithelial cells in the intermediate portion of the ES possess a delayed-rectifier K+ current, which may be involved in membrane stability or in the ion balance between the cytosol and the extracellular environment.
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Affiliation(s)
- D Wu
- Department of Otolaryngology, Kagawa Medical University, Japan
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27
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Kibble JD, Trezise AE, Brown PD. Properties of the cAMP-activated C1- current in choroid plexus epithelial cells isolated from the rat. J Physiol 1996; 496 ( Pt 1):69-80. [PMID: 8910197 PMCID: PMC1160825 DOI: 10.1113/jphysiol.1996.sp021666] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. This study used whole-cell patch clamp and RNA in situ hybridization experiments to determine whether the cAMP-activated C1- current expressed in choroid plexus epithelial cells was carried by the cystic fibrosis transmembrane conductance regulator (CFTR) channel. 2. In patch clamp experiments, inclusion of 0.25 mM cAMP and 375 protein kinase A catalytic subunit (PKA) in the electrode solution caused activation of an inwardly rectifying current (21/23 cells). This current was C1- selective, since the current reversal potential (Erev) was -31 +/- 3 mV with equilibrium potential values for C1- (EC1) and Na+ (ENa) of -44 and 0 mV, respectively. 3. In anion substitution experiments, the relative anion permeability sequence for the inward rectifier was: I- (3.5) > HCO3-(1.5) = C1-(1.0) > Br-(0.6) > aspartate (0.2). 4. The inward rectifier was sensitive to inhibition by a range of known channel inhibitors, including: glibenclamide (100 microns), DIDS (100 and 500 microns), NPPB (100 microns) and Ba2+ (1 mM). 5. In RNA in situ hybridization experiments, using two independent rat CFTR cRNA probes, expression of CFTR could not be detected in epithelial cells from the rat choroid plexus. 6. In conclusion, the cAMP-dependent whole-cell C1- current present in choroid plexus epithelial cells from the rat has properties which are distinctly different from those of CFTR.
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Affiliation(s)
- J D Kibble
- Cell Physiology Group, School of Biological Sciences, University of Manchester, UK.
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28
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Hughes BA, Shaikh A, Ahmad A. Effects of Ba2+ and Cs+ on apical membrane K+ conductance in toad retinal pigment epithelium. THE AMERICAN JOURNAL OF PHYSIOLOGY 1995; 268:C1164-72. [PMID: 7762609 DOI: 10.1152/ajpcell.1995.268.5.c1164] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Intracellular microelectrode techniques were employed to characterize the blocker sensitivity of the K+ conductance (gK) at the apical membrane of the toad retinal pigment epithelium (RPE). Increasing the K+ concentration in the apical bath ([K+]o) from 2 to 5 mM produced a rapid depolarization of the apical membrane potential (VA). The addition of 0.5 mM Ba2+ or 5 mM Cs+ to the apical bath rapidly depolarized VA and increased the transepithelial resistance and ratio of apical-to-basolateral membrane resistance. In the presence of apical Ba2+ or Cs+, the response of VA to delta [K+]o was markedly reduced, indicating that these ions are effective blockers of apical gK. The Ba(2+)- and Cs(+)-induced decreases in the apparent apical-to-basolateral membrane conductance ratio were concentration dependent, with apparent dissociation constants of 17 microM and 0.5 mM, respectively. The apparent blocker sensitivity of apical gK is similar to that previously demonstrated for the inwardly rectifying K+ conductance in isolated toad RPE cells, suggesting that the inwardly rectifying K+ conductance comprises much of apical gK.
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Affiliation(s)
- B A Hughes
- Department of Ophthalmology, University of Michigan, Ann Arbor 48105, USA
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29
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Watson JA, Elliott AC, Brown PD. Serotonin elevates intracellular Ca2+ in rat choroid plexus epithelial cells by acting on 5-HT2C receptors. Cell Calcium 1995; 17:120-8. [PMID: 7736561 DOI: 10.1016/0143-4160(95)90081-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The effects of serotonin (5-HT) on intracellular calcium activity ([Ca2+]i) in epithelial cells from rat choroid plexuses were examined. Experiments were performed on isolated cells which had been maintained in primary culture. ([Ca2+]i) was measured using micro-spectrofluorimetric techniques and the fluorescent indicator Fura-2. 5-HT was found to increase [Ca2+]i in a dose dependent manner. The [Ca2+]i response was biphasic, with an initial peak of [Ca2+]i (due to release from intracellular stores), followed by an elevated plateau phase (the result of calcium influx). The effect of 1 microM 5-HT was inhibited by mesulergine and mianserin (50 nM), which are antagonists of the 5-HT2C receptor. Spiperone and ketanserin (200 nM), less specific 5-HT2 receptor blockers, caused only a slight reduction in the response to 1 microM 5-HT. The [Ca2+]i response decreased upon repeated challenges with 1 microM 5-HT, probably as a result of receptor desensitisation. Taken together, the data suggest that 5-HT acts at 5-HT2C receptors to increase [Ca2+]i in choroid plexus epithelial cells, both by liberating Ca2+ from intracellular stores and by activating a Ca2+ influx pathway.
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Affiliation(s)
- J A Watson
- School of Biological Sciences, University of Manchester, UK
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