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Zuccolini P, Gavazzo P, Pusch M. BK Channel in the Physiology and in the Cancer of Pancreatic Duct: Impact and Reliability of BK Openers. Front Pharmacol 2022; 13:906608. [PMID: 35685628 PMCID: PMC9171006 DOI: 10.3389/fphar.2022.906608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Accepted: 05/10/2022] [Indexed: 11/13/2022] Open
Abstract
BK (KCa 1.1, Slo-1) is a K+ channel characterized by an allosteric regulation of the gating mechanism by Ca2+ binding and voltage, and a high unitary conductance. The channel is expressed in many different tissues, where it is involved in the regulation or the fine-tuning of many physiological processes. Among other organs, BK is expressed in the pancreatic duct, a part of the gland important for the correct ionic composition of the pancreatic juice. Unfortunately, the pancreatic duct is also the site where one of the deadliest cancer types, the pancreatic duct adenocarcinoma (PDAC), develops. In the past years, it has been reported that continuous exposure of cancer cells to BK openers can have a significant impact on cell viability as well as on the ability to proliferate and migrate. Here, we first summarize the main BK channel properties and its roles in pancreatic duct physiology. Then we focus on the potential role of BK as a pharmacological target in PDAC. Moreover, we discuss how results obtained when employing BK activators on cancer cells can, in some cases, be misleading.
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Schnipper J, Dhennin-Duthille I, Ahidouch A, Ouadid-Ahidouch H. Ion Channel Signature in Healthy Pancreas and Pancreatic Ductal Adenocarcinoma. Front Pharmacol 2020; 11:568993. [PMID: 33178018 PMCID: PMC7596276 DOI: 10.3389/fphar.2020.568993] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 09/16/2020] [Indexed: 12/11/2022] Open
Abstract
Pancreatic ductal adenocarcinoma (PDAC) is the fourth most common cause of cancer-related deaths in United States and Europe. It is predicted that PDAC will become the second leading cause of cancer-related deaths during the next decades. The development of PDAC is not well understood, however, studies have shown that dysregulated exocrine pancreatic fluid secretion can contribute to pathologies of exocrine pancreas, including PDAC. The major roles of healthy exocrine pancreatic tissue are secretion of enzymes and bicarbonate rich fluid, where ion channels participate to fine-tune these biological processes. It is well known that ion channels located in the plasma membrane regulate multiple cellular functions and are involved in the communication between extracellular events and intracellular signaling pathways and can function as signal transducers themselves. Hereby, they contribute to maintain resting membrane potential, electrical signaling in excitable cells, and ion homeostasis. Despite their contribution to basic cellular processes, ion channels are also involved in the malignant transformation from a normal to a malignant phenotype. Aberrant expression and activity of ion channels have an impact on essentially all hallmarks of cancer defined as; uncontrolled proliferation, evasion of apoptosis, sustained angiogenesis and promotion of invasion and migration. Research indicates that certain ion channels are involved in the aberrant tumor growth and metastatic processes of PDAC. The purpose of this review is to summarize the important expression, localization, and function of ion channels in normal exocrine pancreatic tissue and how they are involved in PDAC progression and development. As ion channels are suggested to be potential targets of treatment they are furthermore suggested to be biomarkers of different cancers. Therefore, we describe the importance of ion channels in PDAC as markers of diagnosis and clinical factors.
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Affiliation(s)
- Julie Schnipper
- Laboratory of Cellular and Molecular Physiology, UR-4667, University of Picardie Jules Verne, Amiens, France
| | - Isabelle Dhennin-Duthille
- Laboratory of Cellular and Molecular Physiology, UR-4667, University of Picardie Jules Verne, Amiens, France
| | - Ahmed Ahidouch
- Laboratory of Cellular and Molecular Physiology, UR-4667, University of Picardie Jules Verne, Amiens, France.,Department of Biology, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco
| | - Halima Ouadid-Ahidouch
- Laboratory of Cellular and Molecular Physiology, UR-4667, University of Picardie Jules Verne, Amiens, France
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Khalafalla MG, Woods LT, Jasmer KJ, Forti KM, Camden JM, Jensen JL, Limesand KH, Galtung HK, Weisman GA. P2 Receptors as Therapeutic Targets in the Salivary Gland: From Physiology to Dysfunction. Front Pharmacol 2020; 11:222. [PMID: 32231563 PMCID: PMC7082426 DOI: 10.3389/fphar.2020.00222] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 02/18/2020] [Indexed: 12/12/2022] Open
Abstract
Although often overlooked in our daily lives, saliva performs a host of necessary physiological functions, including lubricating and protecting the oral cavity, facilitating taste sensation and digestion and maintaining tooth enamel. Therefore, salivary gland dysfunction and hyposalivation, often resulting from pathogenesis of the autoimmune disease Sjögren's syndrome or from radiotherapy of the head and neck region during cancer treatment, severely reduce the quality of life of afflicted patients and can lead to dental caries, periodontitis, digestive disorders, loss of taste and difficulty speaking. Since their initial discovery in the 1970s, P2 purinergic receptors for extracellular nucleotides, including ATP-gated ion channel P2X and G protein-coupled P2Y receptors, have been shown to mediate physiological processes in numerous tissues, including the salivary glands where P2 receptors represent a link between canonical and non-canonical saliva secretion. Additionally, extracellular nucleotides released during periods of cellular stress and inflammation act as a tissue alarmin to coordinate immunological and tissue repair responses through P2 receptor activation. Accordingly, P2 receptors have gained widespread clinical interest with agonists and antagonists either currently undergoing clinical trials or already approved for human use. Here, we review the contributions of P2 receptors to salivary gland function and describe their role in salivary gland dysfunction. We further consider their potential as therapeutic targets to promote physiological saliva flow, prevent salivary gland inflammation and enhance tissue regeneration.
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Affiliation(s)
- Mahmoud G. Khalafalla
- Department of Biochemistry, University of Missouri, Columbia, MO, United States
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, United States
- Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Lucas T. Woods
- Department of Biochemistry, University of Missouri, Columbia, MO, United States
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, United States
| | - Kimberly J. Jasmer
- Department of Biochemistry, University of Missouri, Columbia, MO, United States
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, United States
| | - Kevin Muñoz Forti
- Department of Biochemistry, University of Missouri, Columbia, MO, United States
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, United States
| | - Jean M. Camden
- Department of Biochemistry, University of Missouri, Columbia, MO, United States
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, United States
| | - Janicke L. Jensen
- Institute of Clinical Dentistry, Section of Oral Surgery and Oral Medicine, University of Oslo, Oslo, Norway
| | - Kirsten H. Limesand
- Department of Nutritional Sciences, University of Arizona, Tucson, AZ, United States
| | - Hilde K. Galtung
- Institute of Oral Biology, Faculty of Dentistry, University of Oslo, Oslo, Norway
| | - Gary A. Weisman
- Department of Biochemistry, University of Missouri, Columbia, MO, United States
- Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, United States
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4
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Lin JP, Chen CQ, Huang LE, Li NN, Yang Y, Zhu SM, Yao YX. Dexmedetomidine Attenuates Neuropathic Pain by Inhibiting P2X7R Expression and ERK Phosphorylation in Rats. Exp Neurobiol 2018; 27:267-276. [PMID: 30181689 PMCID: PMC6120967 DOI: 10.5607/en.2018.27.4.267] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Revised: 08/21/2018] [Accepted: 08/23/2018] [Indexed: 01/24/2023] Open
Abstract
α2-Adrenoceptor agonists attenuate hypersensitivity under neuropathic conditions. However, the mechanisms underlying this attenuation remain largely unknown. In the present study, we explored the potential roles of purinergic receptor 7 (P2X7R)/extracellular signal-regulated kinase (ERK) signaling in the anti-nociceptive effect of dexmedetomidine in a rat model of neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve. An animal model of CCI was adopted to mimic the clinical neuropathic pain state. Behavioral hypersensitivity to mechanical and thermal stimuli was determined by von Frey filament and Hargreaves' tests, and the spinal P2X7R expression level and ERK phosphorylation were analyzed using western blot analysis and immunohistochemistry. In parallel with the development of mechanical and thermal hyperalgesia, a significant increase in P2X7R expression was noted in the ipsilateral spinal cord on day 7 after CCI. Intrathecal administration of dexmedetomidine (2.5 µg) for 3 days not only attenuated neuropathic pain but also inhibited the CCI-induced P2X7R upregulation and ERK phosphorylation. Intrathecal dexmedetomidine administration did not produce obvious effects on locomotor function. The present study demonstrated that dexmedetomidine attenuates the neuropathic pain induced by CCI of the sciatic nerve in rats by inhibiting spinal P2X7R expression and ERK phosphorylation, indicating the potential therapeutic implications of dexmedetomidine administration for the treatment of neuropathic pain.
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Affiliation(s)
- Jia-Piao Lin
- Department of Anesthesia, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, P.R. China
| | - Chao-Qin Chen
- Department of Anesthesia, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, P.R. China
| | - Ling-Er Huang
- Department of Anesthesia, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, P.R. China
| | - Na-Na Li
- Department of Anesthesia, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, P.R. China
| | - Yan Yang
- Centre for Neuroscience, Zhejiang University School of Medicine, Hangzhou 310016, P.R. China
| | - Sheng-Mei Zhu
- Department of Anesthesia, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, P.R. China
| | - Yong-Xing Yao
- Department of Anesthesia, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, P.R. China
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KCa3.1 (IK) modulates pancreatic cancer cell migration, invasion and proliferation: anomalous effects on TRAM-34. Pflugers Arch 2016; 468:1865-1875. [DOI: 10.1007/s00424-016-1891-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Revised: 10/05/2016] [Accepted: 10/06/2016] [Indexed: 12/30/2022]
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Bhattacharya S, Imbery JF, Ampem PT, Giovannucci DR. Crosstalk between purinergic receptors and canonical signaling pathways in the mouse salivary gland. Cell Calcium 2015; 58:589-97. [PMID: 26443524 DOI: 10.1016/j.ceca.2015.09.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Revised: 09/22/2015] [Accepted: 09/25/2015] [Indexed: 01/21/2023]
Abstract
Isolated clusters of mouse parotid acinar cells in combination with live cell imaging were used to explore the crosstalk in molecular signaling between purinergic, cholinergic and adrenergic pathways that integrate to control fluid and protein secretion. This crosstalk was manifested by (1) β-adrenergic receptor activation and amplification of P2X4R evoked Ca(2+) signals, (2) β-adrenergic-induced amplification of P2X7R-evoked Ca(2+) signals and (3) muscarinic receptor induced activation of P2X7Rs via exocytotic activity. The findings from our study reveal that purinoceptor-mediated Ca(2+) signaling is modulated by crosstalk with canonical signaling pathways in parotid acinar cells. Integration of these signals are likely important for dynamic control of saliva secretion to match physiological demand in the parotid gland.
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Affiliation(s)
- Sumit Bhattacharya
- Department of Neurosciences, University of Toledo Medical Center, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - John F Imbery
- Department of Neurosciences, University of Toledo Medical Center, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - Prince Tuffour Ampem
- Department of Neurosciences, University of Toledo Medical Center, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - David R Giovannucci
- Department of Neurosciences, University of Toledo Medical Center, 3000 Arlington Avenue, Toledo, OH 43614, USA.
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Ferreira MJ, McKenna LB, Zhang J, Reichert M, Bakir B, Buza EL, Furth EE, Bogue CW, Rustgi AK, Kaestner KH. Spontaneous Pancreatitis Caused by Tissue-Specific Gene Ablation of Hhex in Mice. Cell Mol Gastroenterol Hepatol 2015; 1:550-569. [PMID: 26740970 PMCID: PMC4698881 DOI: 10.1016/j.jcmgh.2015.06.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
BACKGROUND & AIMS Perturbations in pancreatic ductal bicarbonate secretion cause chronic pancreatitis. The physiologic mechanism of ductal secretion is known, but its transcriptional control is not. We determine the role of the transcription factor hematopoietically expressed homeobox protein (Hhex) in ductal secretion and pancreatitis. METHODS We derived mice with pancreas-specific, Cremediated Hhex gene ablation to determine the requirement of Hhex in the pancreatic duct in early life and in adult stages. Histologic and immunostaining analyses were used to detect the presence of pathology. Pancreatic primary ductal cells were isolated to discover differentially expressed transcripts upon acute Hhex ablation on a cell autonomous level. RESULTS Hhex protein was detected throughout the embryonic and adult ductal trees. Ablation of Hhex in pancreatic progenitors resulted in postnatal ductal ectasia associated with acinar-to-ductal metaplasia, a progressive phenotype that ultimately resulted in chronic pancreatitis. Hhex ablation in adult mice, however, did not cause any detectable pathology. Ductal ectasia in young mice did not result from perturbation of expression of Hnf6, Hnf1β, or the primary cilia genes. RNA-seq analysis of Hhex-ablated pancreatic primary ductal cells showed mRNA levels of the G-protein coupled receptor natriuretic peptide receptor 3 (Npr3), implicated in paracrine signaling, up-regulated by 4.70-fold. CONCLUSIONS Although Hhex is dispensable for ductal cell function in the adult, ablation of Hhex in pancreatic progenitors results in pancreatitis. Our data highlight the critical role of Hhex in maintaining ductal homeostasis in early life and support ductal hypersecretion as a novel etiology of pediatric chronic pancreatitis.
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Affiliation(s)
- Mark J. Ferreira
- Department of Genetics and Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Lindsay B. McKenna
- Department of Genetics and Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Jia Zhang
- Department of Genetics and Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Maximilian Reichert
- Division of Gastroenterology, Department of Medicine, Abramson Cancer Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Basil Bakir
- Division of Gastroenterology, Department of Medicine, Abramson Cancer Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Elizabeth L. Buza
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Emma E. Furth
- Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Clifford W. Bogue
- Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut
| | - Anil K. Rustgi
- Division of Gastroenterology, Department of Medicine, Abramson Cancer Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Klaus H. Kaestner
- Department of Genetics and Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania,Correspondence Address correspondence to: Klaus H. Kaestner, PhD, Department of Genetics, Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, 12–126 Translational Research Center, 3400 Civic Center Boulevard, Philadelphia, Pennsylvania 19104. fax: 215-573-5892.
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Burnstock G. Purinergic signalling in the gastrointestinal tract and related organs in health and disease. Purinergic Signal 2014; 10:3-50. [PMID: 24307520 PMCID: PMC3944042 DOI: 10.1007/s11302-013-9397-9] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 10/24/2013] [Indexed: 01/04/2023] Open
Abstract
Purinergic signalling plays major roles in the physiology and pathophysiology of digestive organs. Adenosine 5'-triphosphate (ATP), together with nitric oxide and vasoactive intestinal peptide, is a cotransmitter in non-adrenergic, non-cholinergic inhibitory neuromuscular transmission. P2X and P2Y receptors are widely expressed in myenteric and submucous enteric plexuses and participate in sympathetic transmission and neuromodulation involved in enteric reflex activities, as well as influencing gastric and intestinal epithelial secretion and vascular activities. Involvement of purinergic signalling has been identified in a variety of diseases, including inflammatory bowel disease, ischaemia, diabetes and cancer. Purinergic mechanosensory transduction forms the basis of enteric nociception, where ATP released from mucosal epithelial cells by distension activates nociceptive subepithelial primary afferent sensory fibres expressing P2X3 receptors to send messages to the pain centres in the central nervous system via interneurons in the spinal cord. Purinergic signalling is also involved in salivary gland and bile duct secretion.
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Affiliation(s)
- Geoffrey Burnstock
- Autonomic Neuroscience Centre, University College Medical School, Rowland Hill Street, London, NW3 2PF, UK,
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Novak I, Haanes KA, Wang J. Acid-base transport in pancreas-new challenges. Front Physiol 2013; 4:380. [PMID: 24391597 PMCID: PMC3868914 DOI: 10.3389/fphys.2013.00380] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Accepted: 12/04/2013] [Indexed: 12/11/2022] Open
Abstract
Along the gastrointestinal tract a number of epithelia contribute with acid or basic secretions in order to aid digestive processes. The stomach and pancreas are the most extreme examples of acid (H(+)) and base (HCO(-) 3) transporters, respectively. Nevertheless, they share the same challenges of transporting acid and bases across epithelia and effectively regulating their intracellular pH. In this review, we will make use of comparative physiology to enlighten the cellular mechanisms of pancreatic HCO(-) 3 and fluid secretion, which is still challenging physiologists. Some of the novel transporters to consider in pancreas are the proton pumps (H(+)-K(+)-ATPases), as well as the calcium-activated K(+) and Cl(-) channels, such as KCa3.1 and TMEM16A/ANO1. Local regulators, such as purinergic signaling, fine-tune, and coordinate pancreatic secretion. Lastly, we speculate whether dys-regulation of acid-base transport contributes to pancreatic diseases including cystic fibrosis, pancreatitis, and cancer.
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Affiliation(s)
- Ivana Novak
- Department of Biology, University of Copenhagen Copenhagen, Denmark
| | | | - Jing Wang
- Department of Biology, University of Copenhagen Copenhagen, Denmark
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Hayashi M, Novak I. Molecular basis of potassium channels in pancreatic duct epithelial cells. Channels (Austin) 2013; 7:432-41. [PMID: 23962792 PMCID: PMC4042478 DOI: 10.4161/chan.26100] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Potassium channels regulate excitability, epithelial ion transport, proliferation, and apoptosis. In pancreatic ducts, K+ channels hyperpolarize the membrane potential and provide the driving force for anion secretion. This review focuses on the molecular candidates of functional K+ channels in pancreatic duct cells, including KCNN4 (KCa3.1), KCNMA1 (KCa1.1), KCNQ1 (Kv7.1), KCNH2 (Kv11.1), KCNH5 (Kv10.2), KCNT1 (KCa4.1), KCNT2 (KCa4.2), and KCNK5 (K2P5.1). We will give an overview of K+ channels with respect to their electrophysiological and pharmacological characteristics and regulation, which we know from other cell types, preferably in epithelia, and, where known, their identification and functions in pancreatic ducts and in adenocarcinoma cells. We conclude by pointing out some outstanding questions and future directions in pancreatic K+ channel research with respect to the physiology of secretion and pancreatic pathologies, including pancreatitis, cystic fibrosis, and cancer, in which the dysregulation or altered expression of K+ channels may be of importance.
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Affiliation(s)
- Mikio Hayashi
- Department of Biology; University of Copenhagen; Copenhagen, Denmark
| | - Ivana Novak
- Department of Biology; University of Copenhagen; Copenhagen, Denmark
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Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) protein is highly expressed in the pancreatic duct epithelia and permits anions and water to enter the ductal lumen. This results in an increased volume of alkaline fluid allowing the highly concentrated proteins secreted by the acinar cells to remain in a soluble state. This work will expound on the pathophysiology and pathology caused by the malfunctioning CFTR protein with special reference to ion transport and acid-base abnormalities both in humans and animal models. We will also discuss the relationship between cystic fibrosis (CF) and pancreatitis, and outline present and potential therapeutic approaches in CF treatment relevant to the pancreas.
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Affiliation(s)
- Michael Wilschanski
- Pediatric Gastroenterology, Hadassah University Hospital, Jerusalem 91240, Israel
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Uridine triphosphate increases proliferation of human cancerous pancreatic duct epithelial cells by activating P2Y2 receptor. Pancreas 2013; 42:680-6. [PMID: 23462325 DOI: 10.1097/mpa.0b013e318271bb4b] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
OBJECTIVES The aim of this study was to investigate the effect of uridine triphosphate (UTP) on the proliferation of human cancerous pancreatic duct epithelial cells. METHODS Proliferation was measured by immunoassay for bromodeoxyuridine incorporation into the pancreatic cell line PANC-1. Effect of UTP was assayed using selective P2 agonist and antagonist, small interfering RNA, intracellular signal inhibitors, and Western blot. RESULTS Incubation of PANC-1 cells with UTP or MRS2768, a selective P2Y2 receptor agonist, resulted in a dose- and time-dependent increase of proliferation. The messenger RNA transcript and protein of P2Y2 receptor were expressed in PANC-1 cells. P2 receptor antagonist suramin and small interfering RNA against P2Y2 receptor significantly decreased the proliferative effect of UTP and MRS2768. Activation of P2Y2 receptor by UTP transduced to phospholipase C, inositol 1,4,5-triphosphate (IP3), and protein kinase C. Uridine triphosphate-induced proliferation was mediated by protein kinase D, Src-family tyrosine kinase, Ca/calmodulin-dependent protein kinase II, phosphatidylinositol 3-kinase (PI3K), Akt, and phospholipase D. Uridine triphosphate increased phosphorylation of Akt through protein kinase C, Src-family tyrosine kinase, Ca/calmodulin-dependent protein kinase II, and PI3K. CONCLUSIONS Uridine triphosphate increases proliferation of human pancreatic duct epithelial cells by activation of P2Y2 receptor and PI3K/Akt pathway. This could be helpful for discovering the long-term roles of P2Y2 receptor in pancreatic cells.
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Ion transport in human pancreatic duct epithelium, Capan-1 cells, is regulated by secretin, VIP, acetylcholine, and purinergic receptors. Pancreas 2013; 42:452-60. [PMID: 22982819 DOI: 10.1097/mpa.0b013e318264c302] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
OBJECTIVES The objective of the study was to establish a solid model of polarized epithelium for human pancreatic ducts, where electrical parameters could be measured as indicators of ion transport. Further, we aimed to determine functional expression of several receptors, in particular, purinergic receptors, and determine their effects on ion transport. METHODS Human adenocarcinoma cell line Capan-1 cells were grown on permeable supports and set in Ussing chambers for electrophysiological recordings. Transepithelial voltage (Vte), resistance, and short-circuit currents (Isc) were measured in response to agonists. RESULTS Secretin, vasoactive intestinal peptide (VIP), acetylcholine, forskolin, ionomycin, adenosine 5'-triphosphate (ATP), uridine 5'-triphosphate (UTP), 3'-O-(4-benzoyl)benzoyl ATP, and adenosine induced lumen negative Vte and Isc. These changes were consistent with anion secretion, as verified in forskolin-stimulated preparations. Extracellular nucleotides, ATP, and UTP, applied from luminal and basolateral sides, caused largest responses: Vte increased up to -5 mV, Isc increased to 20 to 30 μA/cm, and resistance decreased by up to 200 Ω·cm. CONCLUSIONS Transepithelial transport in human pancreatic duct epithelium, Capan-1 cells, is regulated by secretin, VIP, acetylcholine, adenosine, and purinergic P2 receptors; and this human model has a good potential for studies of physiology and pathophysiology of pancreatic duct ion transport.
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Hammami S, Willumsen NJ, Meinild AK, Klaerke DA, Novak I. Purinergic signalling - a possible mechanism for KCNQ1 channel response to cell volume challenges. Acta Physiol (Oxf) 2013; 207:503-15. [PMID: 22805606 DOI: 10.1111/j.1748-1716.2012.02460.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2012] [Revised: 03/11/2012] [Accepted: 05/28/2012] [Indexed: 11/27/2022]
Abstract
AIM A number of K(+) channels are regulated by small, fast changes in cell volume. The mechanisms underlying cell volume sensitivity are not known, but one possible mechanism could be purinergic signalling. Volume activated ATP release could trigger signalling pathways that subsequently lead to ion channel stimulation and cell volume back-regulation. Our aim was to investigate whether volume sensitivity of the voltage-gated K(+) channel, KCNQ1, is dependent on ATP release and regulation by purinergic signalling. METHODS We used Xenopus oocytes heterologously expressing human KCNQ1, KCNE1, water channels (AQP1) and P2Y2 receptors. ATP release was monitored by a luciferin-luciferase assay and ion channel conductance was recorded by two-electrode voltage clamp. RESULTS The luminescence assay showed that oocytes released ATP in response to mechanical, hypoosmotic stimuli and hyperosmotic stimuli. Basal ATP release was approx. three times higher in the KCNQ1 + AQP1 and KCNQ1 injected oocytes compared to the non-injected ones. Exogenously added ATP (0.1 mm) did not have any substantial effect on volume-induced KCNQ1 currents. Nevertheless, apyrase decreased all currents by about 50%. Suramin inhibited about 23% of the KCNQ1 volume sensitivity. Expression of P2Y2 receptors stimulated endogenous Cl(-) channels, but it also led to 68% inhibition of the KCNQ1 currents. Adenosine (0.1 mm) also inhibited the KCNQ1 currents by about 56%. CONCLUSION Xenopus oocytes release ATP in response to mechanical stimuli and cell volume changes. Purinergic P2 and P1 receptors confer some of the KCNQ1 channel volume sensitivity, although endogenous adenosine receptors and expressed P2Y2 receptors do so in the negative direction.
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Affiliation(s)
- S. Hammami
- Department of Biology; University of Copenhagen; Copenhagen; Denmark
| | - N. J. Willumsen
- Department of Biology; University of Copenhagen; Copenhagen; Denmark
| | - A.-K. Meinild
- Department of Biology; University of Copenhagen; Copenhagen; Denmark
| | - D. A. Klaerke
- Department of Physiology and Biochemistry; IBHV, University of Copenhagen; Copenhagen; Denmark
| | - I. Novak
- Department of Biology; University of Copenhagen; Copenhagen; Denmark
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15
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Wang J, Haanes KA, Novak I. Purinergic regulation of CFTR and Ca(2+)-activated Cl(-) channels and K(+) channels in human pancreatic duct epithelium. Am J Physiol Cell Physiol 2013; 304:C673-84. [PMID: 23364268 DOI: 10.1152/ajpcell.00196.2012] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Purinergic agonists have been considered for the treatment of respiratory epithelia in cystic fibrosis (CF) patients. The pancreas, one of the most seriously affected organs in CF, expresses various purinergic receptors. Studies on the rodent pancreas show that purinergic signaling regulates pancreatic secretion. In the present study we aim to identify Cl(-) and K(+) channels in human pancreatic ducts and their regulation by purinergic receptors. Human pancreatic duct epithelia formed by Capan-1 or CFPAC-1 cells were studied in open-circuit Ussing chambers. In Capan-1 cells, ATP/UTP effects were dependent on intracellular Ca(2+). Apically applied ATP/UTP stimulated CF transmembrane conductance regulator (CFTR) and Ca(2+)-activated Cl(-) (CaCC) channels, which were inhibited by CFTRinh-172 and niflumic acid, respectively. The basolaterally applied ATP stimulated CFTR. In CFPAC-1 cells, which have mutated CFTR, basolateral ATP and UTP had negligible effects. In addition to Cl(-) transport in Capan-1 cells, the effects of 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (DC-EBIO) and clotrimazole indicated functional expression of the intermediate conductance K(+) channels (IK, KCa3.1). The apical effects of ATP/UTP were greatly potentiated by the IK channel opener DC-EBIO. Determination of RNA and protein levels revealed that Capan-1 cells have high expression of TMEM16A (ANO1), a likely CaCC candidate. We conclude that in human pancreatic duct cells ATP/UTP regulates via purinergic receptors both Cl(-) channels (TMEM16A/ANO1 and CFTR) and K(+) channels (IK). The K(+) channels provide the driving force for Cl(-)-channel-dependent secretion, and luminal ATP provided locally or secreted from acini may potentiate secretory processes. Future strategies in augmenting pancreatic duct function should consider sidedness of purinergic signaling and the essential role of K(+) channels.
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Affiliation(s)
- Jing Wang
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
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Larsen CK, Leipziger J. P2Y receptors in the gastrointestinal epithelium. ACTA ACUST UNITED AC 2012. [DOI: 10.1002/wmts.74] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Abstract
OBJECTIVES The aim of this study was to investigate the effect of P2Y receptor activation on proliferation of human pancreatic duct epithelial cells. METHODS Proliferation was measured by immunoassay for bromodeoxyuridine incorporation into a pancreatic duct epithelial cell line, PANC-1. Expression of P2Y receptors was examined using quantitative reverse transcription-polymerase chain reaction and Western blot. RESULTS Extracellular nucleotides, adenosine diphosphate (ADP) and uridine diphosphate (UDP), stimulated proliferation of pancreatic duct cells in a concentration-dependent manner. The nucleotide efficacy order was ADP > UDP > uridine triphosphate (UTP) > adenosine triphosphate. P2Y(1) and P2Y(6) receptor blockers, MRS2500 and MRS2578, blocked the effect of ADP and UDP. The signal that transmitted the proliferative activity of ADP and UDP was transducted to phospholipase C, inositol 1,4,5-triphosphate receptor, and protein kinase C. These results indicate involvement of P2Y(1) and P2Y(6) receptors in ADP- and UDP-stimulated proliferation. Pancreatic duct cells expressed the messenger RNA transcripts of P2Y receptors, P2Y(1) , P2Y(2), and P2Y(6), and P2Y(1) and P2Y(6) receptor protein. CONCLUSIONS Extracellular nucleotides increase proliferation of human pancreatic duct epithelial cells by activation of P2Y(1) and P2Y(6) receptors. This provides the basic model for the effect of P2Y receptors on the proliferation of pancreatic duct epithelial cells.
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Hayashi M, Wang J, Hede SE, Novak I. An intermediate-conductance Ca2+-activated K+ channel is important for secretion in pancreatic duct cells. Am J Physiol Cell Physiol 2012; 303:C151-9. [PMID: 22555847 DOI: 10.1152/ajpcell.00089.2012] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Potassium channels play a vital role in maintaining the membrane potential and the driving force for anion secretion in epithelia. In pancreatic ducts, which secrete bicarbonate-rich fluid, the identity of K(+) channels has not been extensively investigated. In this study, we investigated the molecular basis of functional K(+) channels in rodent and human pancreatic ducts (Capan-1, PANC-1, and CFPAC-1) using molecular and electrophysiological techniques. RT-PCR analysis revealed mRNAs for KCNQ1, KCNH2, KCNH5, KCNT1, and KCNT2, as well as KCNN4 coding for the following channels: KVLQT1; HERG; EAG2; Slack; Slick; and an intermediate-conductance Ca(2+)-activated K(+) (IK) channel (K(Ca)3.1). The following functional studies were focused on the IK channel. 5,6-Dichloro-1-ethyl-1,3-dihydro-2H-benzimidazole-2-one (DC-EBIO), an activator of IK channel, increased equivalent short-circuit current (I(sc)) in Capan-1 monolayer, consistent with a secretory response. Clotrimazole, a blocker of IK channel, inhibited I(sc). IK channel blockers depolarized the membrane potential of cells in microperfused ducts dissected from rodent pancreas. Cell-attached patch-clamp single-channel recordings revealed IK channels with an average conductance of 80 pS in freshly isolated rodent duct cells. These results indicated that the IK channels may, at least in part, be involved in setting the resting membrane potential. Furthermore, the IK channels are involved in anion and potassium transport in stimulated pancreatic ducts.
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Affiliation(s)
- Mikio Hayashi
- Department of Biology, August Krogh Building, University of Copenhagen, Denmark.
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Abstract
Pancreatic cells contain specialised stores for ATP. Purinergic receptors (P2 and P1) and ecto-nucleotidases are expressed in both endocrine and exocrine calls, as well as in stromal cells. The pancreas, especially the endocrine cells, were an early target for the actions of ATP. After the historical perspective of purinergic signalling in the pancreas, the focus of this review will be the physiological functions of purinergic signalling in the regulation of both endocrine and exocrine pancreas. Next, we will consider possible interaction between purinergic signalling and other regulatory systems and their relation to nutrient homeostasis and cell survival. The pancreas is an organ exhibiting several serious diseases - cystic fibrosis, pancreatitis, pancreatic cancer and diabetes - and some are associated with changes in life-style and are increasing in incidence. There is upcoming evidence for the role of purinergic signalling in the pathophysiology of the pancreas, and the new challenge is to understand how it is integrated with other pathological processes.
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Affiliation(s)
- G Burnstock
- University College Medical School, Autonomic Neuroscience Centre, Rowland Hill Street, London NW3 2PF, UK.
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Lee MG, Ohana E, Park HW, Yang D, Muallem S. Molecular mechanism of pancreatic and salivary gland fluid and HCO3 secretion. Physiol Rev 2012; 92:39-74. [PMID: 22298651 DOI: 10.1152/physrev.00011.2011] [Citation(s) in RCA: 275] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Fluid and HCO(3)(-) secretion is a vital function of all epithelia and is required for the survival of the tissue. Aberrant fluid and HCO(3)(-) secretion is associated with many epithelial diseases, such as cystic fibrosis, pancreatitis, Sjögren's syndrome, and other epithelial inflammatory and autoimmune diseases. Significant progress has been made over the last 20 years in our understanding of epithelial fluid and HCO(3)(-) secretion, in particular by secretory glands. Fluid and HCO(3)(-) secretion by secretory glands is a two-step process. Acinar cells secrete isotonic fluid in which the major salt is NaCl. Subsequently, the duct modifies the volume and electrolyte composition of the fluid to absorb the Cl(-) and secrete HCO(3)(-). The relative volume secreted by acinar and duct cells and modification of electrolyte composition of the secreted fluids varies among secretory glands to meet their physiological functions. In the pancreas, acinar cells secrete a small amount of NaCl-rich fluid, while the duct absorbs the Cl(-) and secretes HCO(3)(-) and the bulk of the fluid in the pancreatic juice. Fluid secretion appears to be driven by active HCO(3)(-) secretion. In the salivary glands, acinar cells secrete the bulk of the fluid in the saliva that is driven by active Cl(-) secretion and contains high concentrations of Na(+) and Cl(-). The salivary glands duct absorbs both the Na(+) and Cl(-) and secretes K(+) and HCO(3)(-). In this review, we focus on the molecular mechanism of fluid and HCO(3)(-) secretion by the pancreas and salivary glands, to highlight the similarities of the fundamental mechanisms of acinar and duct cell functions, and to point out the differences to meet gland-specific secretions.
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Affiliation(s)
- Min Goo Lee
- Department of Pharmacology, Yonsei University College of Medicine, Seoul, Korea
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21
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Novak I. Purinergic signalling in epithelial ion transport: regulation of secretion and absorption. Acta Physiol (Oxf) 2011; 202:501-22. [PMID: 21073662 DOI: 10.1111/j.1748-1716.2010.02225.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intracellular ATP, the energy source for many reactions, is crucial for the activity of plasma membrane pumps and, thus, for the maintenance of transmembrane ion gradients. Nevertheless, ATP and other nucleotides/nucleosides are also extracellular molecules that regulate diverse cellular functions, including ion transport. In this review, I will first introduce the main components of the extracellular ATP signalling, which have become known as the purinergic signalling system. With more than 50 components or processes, just at cell membranes, it ranks as one of the most versatile signalling systems. This multitude of system components may enable differentiated regulation of diverse epithelial functions. As epithelia probably face the widest variety of potential ATP-releasing stimuli, a special attention will be given to stimuli and mechanisms of ATP release with a focus on exocytosis. Subsequently, I will consider membrane transport of major ions (Cl(-) , HCO(3)(-) , K(+) and Na(+) ) and integrate possible regulatory functions of P2Y2, P2Y4, P2Y6, P2Y11, P2X4, P2X7 and adenosine receptors in some selected epithelia at the cellular level. Some purinergic receptors have noteworthy roles. For example, many studies to date indicate that the P2Y2 receptor is one common denominator in regulating ion channels on both the luminal and basolateral membranes of both secretory and absorptive epithelia. In exocrine glands though, P2X4 and P2X7 receptors act as cation channels and, possibly, as co-regulators of secretion. On an organ level, both receptor types can exert physiological functions and together with other partners in the purinergic signalling, integrated models for epithelial secretion and absorption are emerging.
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Affiliation(s)
- I Novak
- Department of Biology, August Krogh Building, University of Copenhagen, Denmark.
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Novak I, Wang J, Henriksen KL, Haanes KA, Krabbe S, Nitschke R, Hede SE. Pancreatic bicarbonate secretion involves two proton pumps. J Biol Chem 2010; 286:280-9. [PMID: 20978133 DOI: 10.1074/jbc.m110.136382] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Pancreas secretes fluid rich in digestive enzymes and bicarbonate. The alkaline secretion is important in buffering of acid chyme entering duodenum and for activation of enzymes. This secretion is formed in pancreatic ducts, and studies to date show that plasma membranes of duct epithelium express H(+)/HCO(3)(-) transporters, which depend on gradients created by the Na(+)/K(+)-ATPase. However, the model cannot fully account for high-bicarbonate concentrations, and other active transporters, i.e. pumps, have not been explored. Here we show that pancreatic ducts express functional gastric and non-gastric H(+)-K(+)-ATPases. We measured intracellular pH and secretion in small ducts isolated from rat pancreas and showed their sensitivity to H(+)-K(+) pump inhibitors and ion substitutions. Gastric and non-gastric H(+)-K(+) pumps were demonstrated on RNA and protein levels, and pumps were localized to the plasma membranes of pancreatic ducts. Quantitative analysis of H(+)/HCO(3)(-) and fluid transport shows that the H(+)-K(+) pumps can contribute to pancreatic secretion in several species. Our results call for revision of the bicarbonate transport physiology in pancreas, and most likely other epithelia. Furthermore, because pancreatic ducts play a central role in several pancreatic diseases, it is of high relevance to understand the role of H(+)-K(+) pumps in pathophysiology.
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Affiliation(s)
- Ivana Novak
- Department of Biology, August Krogh Building, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen, Denmark.
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23
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Novak I, Jans IM, Wohlfahrt L. Effect of P2X(7) receptor knockout on exocrine secretion of pancreas, salivary glands and lacrimal glands. J Physiol 2010; 588:3615-27. [PMID: 20643770 DOI: 10.1113/jphysiol.2010.190017] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The purinergic P2X(7) receptors are expressed in different cell types where they have varied functions, including regulation of cell survival. The P2X(7) receptors are also expressed in exocrine glands, but their integrated role in secretion is unclear. The aim of our study was to determine whether the P2X(7) receptors affect fluid secretion in pancreas, salivary glands and tear glands. We monitored gland secretions in in vivo preparations of wild-type and P2X(7)(-/-) (Pfizer) mice stimulated with pilocarpine. In cell preparations from pancreas, parotid and lacrimal glands we measured ATP release and intracellular Ca(2+) activity using Fura-2. The data showed that pancreatic secretion and salivary secretions were reduced in P2X(7)(-/-) mice, and in contrast, tear secretion was increased in P2X(7)(-/-) mice. The secretory phenotype was also dependent on the sex of the animal, such that males were more dependent on the P2X(7) receptor expression. ATP release in all cell preparations could be elicited by carbachol and other agonists, and this was independent of the P2X(7) receptor expression. ATP and carbachol increased intracellular Ca(2+) activity, but responses depended on the gland type, presence of the P2X(7) receptor and the sex of the animal. Together, these results demonstrate that cholinergic stimulation leads to release of ATP that can via P2X(7) receptors up-regulate pancreatic and salivary secretion but down-regulate tear secretion. Our data also indicate that there is an interaction between purinergic and cholinergic receptor signalling and that function of the P2X(7) receptor is suppressed in females. We conclude that the P2X(7) receptors are important in short-term physiological regulation of exocrine gland secretion.
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Affiliation(s)
- Ivana Novak
- Department of Biology, August Krogh Building, Universitetsparken 13, University of Copenhagen, DK 2100 Copenhagen Ø, Denmark.
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24
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Abstract
ATP is released from pancreatic acini in response to cholinergic and hormonal stimulation. The same stimuli cause exocytosis of ZG (zymogen granules) and release of digestive enzymes. The aim of the present study was to determine whether ZG stored ATP and to characterize the uptake mechanism for ATP transport into the ZG. ZG were isolated and the ATP content was measured using luciferin/luciferase assays and was related to protein in the sample. The estimate of ATP concentration in freshly isolated granules was 40-120 microM. The ATP uptake had an apparent Km value of 4.9+/-2.1 mM when granules were incubated without Mg2+ and a Km value of 0.47+/-0.05 mM in the presence of Mg2+, both in pH 6.0 buffers. The uptake of ATP was significantly higher at pH 7.2 compared with pH 6.0 solutions. The anion transport blockers DIDS (4,4'-di-isothiocyanostilbene-2,2'-disulfonate) and Evans Blue inhibited ATP transport. Western blot analysis on the ZG showed the presence of VNUT (vesicular nucleotide transporter). Together, these findings indicate that VNUT may be responsible for the ATP uptake into ZG. Furthermore, the present study shows the presence of ATP together with digestive enzymes in ZG. This indicates that co-released ATP would regulate P2 receptors in pancreatic ducts and, thus, ductal secretion, and this would aid delivery of enzymes to the duodenum.
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Burnstock G, Fredholm BB, North RA, Verkhratsky A. The birth and postnatal development of purinergic signalling. Acta Physiol (Oxf) 2010; 199:93-147. [PMID: 20345419 DOI: 10.1111/j.1748-1716.2010.02114.x] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The purinergic signalling system is one of the most ancient and arguably the most widespread intercellular signalling system in living tissues. In this review we present a detailed account of the early developments and current status of purinergic signalling. We summarize the current knowledge on purinoceptors, their distribution and role in signal transduction in various tissues in physiological and pathophysiological conditions.
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Affiliation(s)
- G Burnstock
- Autonomic Neuroscience Centre, Royal Free and University College Medical School, London, UK.
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Yang C, Su L, Wang Y, Liu L. UTP regulation of ion transport in alveolar epithelial cells involves distinct mechanisms. Am J Physiol Lung Cell Mol Physiol 2009; 297:L439-54. [PMID: 19542245 DOI: 10.1152/ajplung.90268.2008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
UTP is known to regulate alveolar fluid clearance. However, the relative contribution of alveolar type I cells and type II cells to this process is unknown. In this study, we investigated the effects of UTP on ion transport in type I-like cell (AEC I) and type II-like cell (AEC II) monolayers. Luminal treatment of cell monolayers with UTP increased short-circuit current (I(sc)) of AEC II but decreased I(sc) of AEC I. The Cl(-) channel blockers NPPB and DIDS inhibited the UTP-induced changes in I(sc) (DeltaIsc) in both types of cells. Amiloride, an inhibitor of epithelial Na(+) channels (ENaC), abolished the UTP-induced DeltaI(sc) in AEC I, but not in AEC II. The general blocker of K(+) channels, BaCl(2), eliminated the UTP-induced DeltaI(sc) in AEC II, but not in AEC I. The intermediate conductance (IK(Ca)) blocker, clofilium, also blocked the UTP effect in AEC II. The signal transduction pathways mediated by UTP were the same in AEC I and AEC II. Furthermore, UTP increased Cl(-) secretion in AEC II and Cl(-) absorption in AEC I. Our results suggest that UTP induces opposite changes in I(sc) in AEC I and AEC II, likely due to the reversed Cl(-) flux and different contributions of ENaC and IK(Ca). Our results further imply a new concept that type II cells contribute to UTP-induced fluid secretion and type I cells contribute to UTP-induced fluid absorption in alveoli.
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Affiliation(s)
- Chuanxiu Yang
- Lundberg-Kienlen Lung Biology and Toxicology Laboratory, Department of Physiological Sciences, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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Heitzmann D, Warth R. Physiology and pathophysiology of potassium channels in gastrointestinal epithelia. Physiol Rev 2008; 88:1119-82. [PMID: 18626068 DOI: 10.1152/physrev.00020.2007] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Epithelial cells of the gastrointestinal tract are an important barrier between the "milieu interne" and the luminal content of the gut. They perform transport of nutrients, salts, and water, which is essential for the maintenance of body homeostasis. In these epithelia, a variety of K(+) channels are expressed, allowing adaptation to different needs. This review provides an overview of the current literature that has led to a better understanding of the multifaceted function of gastrointestinal K(+) channels, thereby shedding light on pathophysiological implications of impaired channel function. For instance, in gastric mucosa, K(+) channel function is a prerequisite for acid secretion of parietal cells. In epithelial cells of small intestine, K(+) channels provide the driving force for electrogenic transport processes across the plasma membrane, and they are involved in cell volume regulation. Fine tuning of salt and water transport and of K(+) homeostasis occurs in colonic epithelia cells, where K(+) channels are involved in secretory and reabsorptive processes. Furthermore, there is growing evidence for changes in epithelial K(+) channel expression during cell proliferation, differentiation, apoptosis, and, under pathological conditions, carcinogenesis. In the future, integrative approaches using functional and postgenomic/proteomic techniques will help us to gain comprehensive insights into the role of K(+) channels of the gastrointestinal tract.
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Affiliation(s)
- Dirk Heitzmann
- Institute of Physiology and Clinic and Policlinic for Internal Medicine II, Regensburg, Germany
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Purinergic receptors and gastrointestinal secretomotor function. Purinergic Signal 2008; 4:213-36. [PMID: 18604596 DOI: 10.1007/s11302-008-9104-4] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2007] [Accepted: 04/07/2008] [Indexed: 02/06/2023] Open
Abstract
Secretomotor reflexes in the gastrointestinal (GI) tract are important in the lubrication and movement of digested products, absorption of nutrients, or the diarrhea that occurs in diseases to flush out unwanted microbes. Mechanical or chemical stimulation of mucosal sensory enterochromaffin (EC) cells triggers release of serotonin (5-HT) (among other mediators) and initiates local reflexes by activating intrinsic primary afferent neurons of the submucous plexus. Signals are conveyed to interneurons or secretomotor neurons to stimulate chloride and fluid secretion. Inputs from myenteric neurons modulate secretory rates and reflexes, and special neural circuits exist to coordinate secretion with motility. Cellular components of secretomotor reflexes variably express purinergic receptors for adenosine (A1, A2a, A2b, or A3 receptors) or the nucleotides adenosine 5'-triphosphate (ATP), adenosine diphosphate (ADP), uridine 5'-triphosphate (UTP), or uridine diphosphate (UDP) (P2X(1-7), P2Y(2), P2Y(4), P2Y(6), P2Y(12) receptors). This review focuses on the emerging concepts in our understanding of purinergic regulation at these receptors, and in particular of mechanosensory reflexes. Purinergic inhibitory (A(1), A(3), P2Y(12)) or excitatory (A(2), P2Y(1)) receptors modulate mechanosensitive 5-HT release. Excitatory (P2Y(1), other P2Y, P2X) or inhibitory (A(1), A(3)) receptors are involved in mechanically evoked secretory reflexes or "neurogenic diarrhea." Distinct neural (pre- or postsynaptic) and non-neural distribution profiles of P2X(2), P2X(3), P2X(5), P2Y(1), P2Y(2), P2Y(4), P2Y(6), or P2Y(12) receptors, and for some their effects on neurotransmission, suggests their role in GI secretomotor function. Luminal A(2b), P2Y(2), P2Y(4), and P2Y(6) receptors are involved in fluid and Cl(-), HCO(3) (-), K(+), or mucin secretion. Abnormal receptor expression in GI diseases may be of clinical relevance. Adenosine A(2a) or A(3) receptors are emerging as therapeutic targets in inflammatory bowel diseases (IBD) and gastroprotection; they can also prevent purinergic receptor abnormalities and diarrhea. Purines are emerging as fundamental regulators of enteric secretomotor reflexes in health and disease.
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Novak I. Purinergic receptors in the endocrine and exocrine pancreas. Purinergic Signal 2007; 4:237-53. [PMID: 18368520 DOI: 10.1007/s11302-007-9087-6] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Accepted: 11/06/2007] [Indexed: 11/28/2022] Open
Abstract
The pancreas is a complex gland performing both endocrine and exocrine functions. In recent years there has been increasing evidence that both endocrine and exocrine cells possess purinergic receptors, which influence processes such as insulin secretion and epithelial ion transport. Most commonly, these processes have been viewed separately. In beta cells, stimulation of P2Y(1) receptors amplifies secretion of insulin in the presence of glucose. Nucleotides released from secretory granules could also contribute to autocrine/paracrine regulation in pancreatic islets. In addition to P2Y(1) receptors, there is also evidence for other P2 and adenosine receptors in beta cells (P2Y(2), P2Y(4), P2Y(6), P2X subtypes and A(1) receptors) and in glucagon-secreting alpha cells (P2X(7), A(2) receptors). In the exocrine pancreas, acini release ATP and ATP-hydrolysing and ATP-generating enzymes. P2 receptors are prominent in pancreatic ducts, and several studies indicate that P2Y(2), P2Y(4), P2Y(11), P2X(4) and P2X(7) receptors could regulate secretion, primarily by affecting Cl(-) and K(+) channels and intracellular Ca(2+) signalling. In order to understand the physiology of the whole organ, it is necessary to consider the full complement of purinergic receptors on different cells as well as the structural and functional relation between various cells within the whole organ. In addition to the possible physiological function of purinergic receptors, this review analyses whether the receptors could be potential therapeutic targets for drug design aimed at treatment of pancreatic diseases.
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Affiliation(s)
- I Novak
- Department of Biosciences, University of Copenhagen, August Krogh Building, Universitetsparken 13, 2100, Copenhagen Ø, Denmark,
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Novak I, Hede SE, Hansen MR. Adenosine receptors in rat and human pancreatic ducts stimulate chloride transport. Pflugers Arch 2007; 456:437-47. [PMID: 18057956 DOI: 10.1007/s00424-007-0403-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2007] [Accepted: 11/15/2007] [Indexed: 11/26/2022]
Abstract
Previously, we have shown that pancreatic acini release adenosine triphosphate (ATP) and ATP-handling enzymes, and pancreatic ducts express various purinergic P2 receptors. The aim of the present study was to establish whether pancreatic ducts also express adenosine receptors and whether these could be involved in secretory processes, which involve cystic fibrosis transmembrane regulator (CFTR) Cl- channels or Ca2+-activated Cl- channels and H(+)/HCO(-)(3) transporters. Reverse transcriptase polymerase chain reaction analysis on rat pancreatic ducts and human duct cell adenocarcinoma lines showed that they express A1, A2A, A2B, and A3 receptors. Real-time PCR revealed relatively low messenger RNA levels of adenosine receptors compared to beta-actin; the rank order for the receptors was A2A>A2B>or=A3>>A1 for rat pancreas and A2B>A2A>>A3>or=A1 for duct cell lines. Whole-cell patch-clamp recordings on rat pancreatic ducts showed that, in about half of the recordings, adenosine depolarized the membrane voltage, and this was because of the opening of Cl- channels. Using a Cl--sensitive fluorophore and single-cell imaging on duct cell lines, it was found that 58% of PANC-1 cells responded to adenosine, whereas only 9% of CFPAC-1 cells responded. Adenosine elicited Ca2+ signals only in a few rat and human duct cells, which did not seem to correlate with Cl- signals. A2A receptors were localized in the luminal membranes of rat pancreatic ducts, plasma membrane of many PANC-1 cells, but only a few CFPAC-1 cells. Taken together, our data indicate that A2A receptors open Cl- channels in pancreatic ducts cells with functional CFTR. We propose that adenosine can stimulate pancreatic secretion and, thereby, is an active player in the acini-to-duct signaling.
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Affiliation(s)
- Ivana Novak
- Department of Biosciences, August Krogh Building, University of Copenhagen, Universitetsparken 13, 2100 Copenhagen, Denmark.
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Dubyak GR. Go it alone no more--P2X7 joins the society of heteromeric ATP-gated receptor channels. Mol Pharmacol 2007; 72:1402-5. [PMID: 17895406 DOI: 10.1124/mol.107.042077] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
P2X receptors (P2XR) function as ATP-gated nonselective ion channels permeable to Na+, K+, and Ca2+, and they are expressed in a wide range of excitable, epithelial/endothelial, and immune effector cell types. The channels are trimeric complexes composed of protein subunits encoded by seven different P2XR genes expressed in mammalian and other vertebrate genomes. Current genetic, biochemical, and/or physiological evidence indicates that the extended family of functional P2X receptors includes six homomeric channels composed of P2X1, P2X2, P2X3, P2X4, P2X5, or P2X7 subunits and six heteromeric channels that involve subunit pairings of P2X1/P2X2, P2X1/P2X4, P2X1/P2X5, P2X2/P2X3, P2X2/P2X6, or P2X4/P2X6. Thus, all P2XR subtypes--with the salient exception of P2X7R--have previously been implicated in the assembly of heteromeric ATP-gated ion channels that can comprise unique pharmacological targets in different tissues. The assumed "go-it alone" function of the P2X7R has important implications because agents that target this particular receptor have been proposed as useful therapeutics in various autoinflammatory diseases or amelioration of inflammatory pain. However, this assumption and the interpretations based on it now require reevaluation in light of a new report in this issue of Molecular Pharmacology (p. 1447) that provides convincing biochemical and electrophysiological evidence for the existence of P2X4/P2X7 heteromeric receptors.
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Affiliation(s)
- George R Dubyak
- Department of Physiology and Biophysics, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA.
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Szucs A, Demeter I, Burghardt B, Ovári G, Case RM, Steward MC, Varga G. Vectorial bicarbonate transport by Capan-1 cells: a model for human pancreatic ductal secretion. Cell Physiol Biochem 2007; 18:253-64. [PMID: 17167230 DOI: 10.1159/000097672] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/11/2006] [Indexed: 11/19/2022] Open
Abstract
Human pancreatic ducts secrete a bicarbonate-rich fluid but our knowledge of the secretory process is based mainly on studies of animal models. Our aim was to determine whether the HCO(3)(-) transport mechanisms in a human ductal cell line are similar to those previously identified in guinea-pig pancreatic ducts. Intracellular pH was measured by microfluorometry in Capan-1 cell monolayers grown on permeable filters and loaded with BCECF. Epithelial polarization was assessed by immunolocalization of occludin. Expression of mRNA for key electrolyte transporters and receptors was evaluated by RT-PCR. Capan-1 cells grown on permeable supports formed confluent, polarized monolayers with well developed tight junctions. The recovery of pH(i) from an acid load, induced by a short NH(4)(+) pulse, was mediated by Na(+)-dependent transporters located exclusively at the basolateral membrane. One was independent of HCO(3)(-) and blocked by EIPA (probably NHE1) while the other was HCO(3)(-)-dependent and blocked by H(2)DIDS (probably pNBC1). Changes in pH(i) following blockade of basolateral HCO(3)(-) accumulation confirmed that the cells achieve vectorial HCO(3)(-) secretion. Dose-dependent increases in HCO(3)(-) secretion were observed in response to stimulation of both secretin and VPAC receptors. ATP and UTP applied to the apical membrane stimulated HCO(3)(-) secretion but were inhibitory when applied to the basolateral membrane. HCO(3)(-) secretion in guinea-pig ducts and Capan-1 cell monolayers share many common features, suggesting that the latter is an excellent model for studies of human pancreatic HCO(3)(-) secretion.
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Affiliation(s)
- Akos Szucs
- Molecular Oral Biology Research Group, Department of Oral Biology, Semmelweis University and Hungarian Academy of Sciences, Budapest, Hungary
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Garcia-Marcos M, Pochet S, Marino A, Dehaye JP. P2X7 and phospholipid signalling: The search of the “missing link” in epithelial cells. Cell Signal 2006; 18:2098-104. [PMID: 16815675 DOI: 10.1016/j.cellsig.2006.05.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2006] [Accepted: 05/11/2006] [Indexed: 11/22/2022]
Abstract
The purinergic receptor P2X(7) is widely expressed in epithelial cells. This receptor shares in common with the other P2X receptors the ability to form a non-selective cation channel. On the other hand, the COOH terminus of P2X(7) seems to allow this receptor to couple to a spectrum of downstream effectors responsible for the regulation of cell death and pore formation among other functions. However, the coupling of P2X(7) to these downstream effectors, as well as the identity of possible adapters directly interacting with the receptor, remains poorly understood. Here we review the ability of P2X(7) to activate phospholipid signalling pathways in epithelial cells and propose this step as a possible link between the receptor and other downstream effectors. The P2X(7) ability to control the cellular levels of several lipid messengers (PA, AA, DAG, ceramide, etc.) through the modulation of phospholipases (C, A(2), D) and neutral sphingomyelinase is described. These pathways are sometimes regulated independently of the channel function of the receptor. Recent data concerning P2X(7) localization in lipid rafts is also discussed in relation to the coupling to these pathways and dissociation from channel function.
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Affiliation(s)
- Mikel Garcia-Marcos
- Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias, Universidad del Pais Vasco, Barrio Sarriena S/N, Leioa, 48080 Bilbao, Spain
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34
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Hegyi P, Rakonczay Z. The inhibitory pathways of pancreatic ductal bicarbonate secretion. Int J Biochem Cell Biol 2006; 39:25-30. [PMID: 16996776 DOI: 10.1016/j.biocel.2006.07.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2006] [Revised: 06/26/2006] [Accepted: 07/31/2006] [Indexed: 10/24/2022]
Abstract
Pancreatic duct cells secrete the HCO(3)(-) ions found in pancreatic juice. While the regulatory pathways that stimulate pancreatic ductal HCO(3)(-) secretion are well described, little is known about inhibitory pathways, apart from the fact that they exist. Nevertheless, such inhibitory pathways may be physiologically important in terms of limiting the hydrostatic pressure within the lumen of the duct, and in terms switching off pancreatic secretion after a meal. Methionine encephalin, insulin, somatostatin, peptide YY, substance P, basolaterally applied adenosine triphosphate, arginine vasopressin, 5-hydroxytryptamine and epidermal growth factor have all been shown to inhibit fluid and/or HCO(3)(-) secretion from pancreatic ducts. Importantly, most of these inhibitors have been shown to reduce secretion in isolated pancreatic ducts, so they must act directly on the ductal epithelium. This brief review provides an overview of our current knowledge of the inhibitors, and inhibitory pathways of pancreatic ductal secretion. SIGNALLING NETWORK FACTS: Methionine encephalin, insulin, somatostatin, peptide YY, substance P, basolaterally applied adenosine triphosphate, arginine vasopressin, 5-hydroxytryptamine and epidermal growth factor have all been shown to inhibit fluid and/or HCO(3)(-) secretion from pancreatic ducts. The inhibition of pancreatic secretion can be mediated by indirect (decreased cholinergic or increased adrenergic stimulation, decreased release of stimulatory hormones) and direct (inhibitory hormone or neurotransmitter acting on the duct cells) mechanisms.
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Affiliation(s)
- Péter Hegyi
- First Department of Medicine, Faculty of Medicine, University of Szeged, Koranyi fasor 8-10, Szeged H6720, Hungary.
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35
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Yegutkin GG, Samburski SS, Jalkanen S, Novak I. ATP-consuming and ATP-generating enzymes secreted by pancreas. J Biol Chem 2006; 281:29441-7. [PMID: 16885159 DOI: 10.1074/jbc.m602480200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Pancreatic acini release ATP in response to various stimuli, including cholecystokinin octapeptide (CCK-8), as we show in the present study. There were indications that pancreatic juice also contains enzymes that could hydrolyze ATP during its passage through the ductal system. The aim of this study was to determine which ATP-degrading and possibly ATP-generating enzymes were present in pancreatic secretion. For this purpose, pancreatic juice was collected from anesthetized rats stimulated with infusion of CCK-8. Purine-converting activities in juice samples were assayed by TLC using either [gamma-(32)P]ATP or (14)C/(3)H-labeled and unlabeled nucleotides as appropriate substrates. Data show that the juice contains the enzyme ecto-nucleoside triphosphate diphosphohydrolase that can hydrolyze both [(14)C]ATP and [(3)H]ADP about equally well, i.e. CD39. Reverse-phase high-performance liquid chromatography analysis additionally shows that this enzyme has broad substrate specificity toward other nucleotides, UTP, UDP, ITP, and IDP. In addition, secretion contains ecto-5'-nucleotidase, CD73, further converting [(3)H]AMP to adenosine. Along with highly active hydrolytic enzymes, there were also ATP-generating enzymes in pancreatic juice, adenylate kinase, and NDP kinase, capable of sequentially phosphorylating AMP via ADP to ATP. Activities of nonspecific phosphatases, nucleotide pyrophosphatase/phosphodiesterases, and adenosine deaminase were negligible. Taken together, CCK-8 stimulation of pancreas causes release of both ATP-consuming and ATP-generating enzymes into pancreatic juice. This newly discovered richness of secreted enzymes underscores the importance of purine signaling between acini and pancreatic ducts lumen and implies regulation of the purine-converting enzymes release.
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Affiliation(s)
- Gennady G Yegutkin
- MediCity Research Laboratory and Department of Medical Microbiology, Turku University and National Public Health Institute, FIN-2050 Turku, Finland
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Invited Lectures : Overviews Purinergic signalling: past, present and future. Purinergic Signal 2006; 2:1-324. [PMID: 18404494 PMCID: PMC2096525 DOI: 10.1007/s11302-006-9006-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/02/2006] [Indexed: 12/11/2022] Open
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Palmer ML, Lee SY, Carlson D, Fahrenkrug S, O'Grady SM. Stable knockdown of CFTR establishes a role for the channel in P2Y receptor-stimulated anion secretion. J Cell Physiol 2006; 206:759-70. [PMID: 16245306 DOI: 10.1002/jcp.20519] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
P2Y receptor regulation of anion secretion was investigated in porcine endometrial gland (PEG) epithelial cells. P2Y2, P2Y4, and P2Y6 receptors were detected in monolayers of PEG cells and immunocytochemistry indicated that P2Y4 receptors were located in the apical membrane. Apical membrane current measurements showed that Ca2+-dependent and PKC-dependent Cl- channels were activated following treatment with uridine triphosphate (UTP) (5 microM). Current-voltage relationships comparing calcium-dependent and PKC-dependent UTP responses under biionic conditions showed significant differences in selectivity between Cl-)and I- for the PKC-dependent conductance (P(I)/P(Cl) = 0.76), but not for Ca2+-dependent conductance (PI/P(Cl) = 1.02). The I-/Cl- permeability ratio for the PKC-dependent conductance was identical to that measured for 8-cpt cAMP. Furthermore, PKC stimulation using phorbol 12-myristate 13-acetate (PMA) activated an apical membrane Cl- conductance that was blocked by the CFTR selective inhibitor, CFTRinh-172. CFTR silencing, accomplished by stable expression of small hairpin RNAs (shRNA), blocked the PKC-activated conductance associated with UTP stimulation and provided definitive evidence of a role for CFTR in anion secretion. CFTR activation increased the initial magnitude of Cl- secretion, and provided a more sustained secretory response compared to conditions where only Ca2+-activated Cl- channels were activated by UTP. Measurements of [cAMP]i following UTP and PMA stimulation were not significantly different than untreated controls. Thus, these results demonstrate that UTP and PMA activation of CFTR occurs independently of increases in intracellular cAMP and extend the findings of earlier studies of CFTR regulation by PKC in Xenopus oocytes to a mammalian anion secreting epithelium.
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Affiliation(s)
- Melissa L Palmer
- Department of Physiology, University of Minnesota, St. Paul, Minnesota 55108, USA
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Zhao LF, Iwasaki Y, Oki Y, Tsugita M, Taguchi T, Nishiyama M, Takao T, Kambayashi M, Hashimoto K. Purinergic receptor ligands stimulate pro-opiomelanocortin gene expression in AtT-20 pituitary corticotroph cells. J Neuroendocrinol 2006; 18:273-8. [PMID: 16503922 DOI: 10.1111/j.1365-2826.2006.01416.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Although recent studies have suggested that purinergic receptors are expressed in the anterior pituitary gland, their involvement in the regulation of pituitary hormone gene expression is not completely understood. In the present study, we examined the expression of purinergic receptors and the effects of purinergic receptor ligands on pro-opiomelanocortin (POMC) gene expression, in AtT20 mouse corticotroph cells. We identified the expression of most of the purinergic receptor subtypes (A1, A2, P2X1, 3-7, P2Y1, 2, 4) mRNAs, analysed by the reverse transcriptase-polymerase chain reaction. We also found that adenosine and ATP, two representative and endogenous agonists of A1-3 and P2X/P2Y receptors, respectively, stimulated the 5'-promoter activity of the POMC gene in a dose- and time-related manner. When these ligands were simultaneously used with corticotrophin-releasing hormone (CRH), effects that were more than additive were observed, suggesting an enhancing role of these compounds in CRH-mediated adrenocorticotrophic hormone (ACTH) synthesis. These ligands also stimulated the expression of transcription factors involved in the regulation of the POMC gene, but did not enhance ACTH secretion. Finally, the positive effect of adenosine as well as CRH was completely inhibited by the protein kinase A inhibitor H89, whereas that of ATP was not influenced, indicating that different intracellular signalling pathways mediate these effects. Altogether, our results suggest a stimulatory role for these purinergic receptor ligands in the regulation of POMC gene expression in corticotroph cells. Because adenosine and ATP are known to be produced within the pituitary gland, it is possible they may be acting in an autocrine/paracrine fashion.
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Affiliation(s)
- L-F Zhao
- Department of Endocrinology, Metabolism and Nephrology, Kochi Medical School, Kochi University, Nankoku, Japan
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39
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Hede SE, Amstrup J, Klaerke DA, Novak I. P2Y2 and P2Y4 receptors regulate pancreatic Ca(2+)-activated K+ channels differently. Pflugers Arch 2005; 450:429-36. [PMID: 16075244 DOI: 10.1007/s00424-005-1433-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Accepted: 04/04/2005] [Indexed: 10/25/2022]
Abstract
Extracellular ATP is an important regulator of transepithelial transport in a number of tissues. In pancreatic ducts, we have shown that ATP modulates epithelial K+ channels via purinergic receptors, most likely the P2Y2 and P2Y4 receptors, but the identity of the involved K+ channels was not clear. In this study, we show by RT-PCR analysis that rat pancreatic ducts express Ca(2+)-activated K+ channels of intermediate conductance (IK) and big conductance (BK), but not small conductance (SK). Possible interactions between P2Y receptors and these Ca(2+)-activated K+ channels were examined in co-expression experiments in Xenopus laevis oocytes. K+ channel activity was measured electrophysiologically in oocytes stimulated with UTP (0.1 mM). UTP stimulation of oocytes expressing P2Y4 receptors and BK channels resulted in a 30% increase in the current through the expressed channels. In contrast, stimulation of P2Y2 receptors led to a 20% inhibition of co-expressed BK channel activity, a response that was sensitive to TEA. Furthermore, co-expression of IK channels with P2Y4 and P2Y2 receptors resulted in a large hyperpolarization and 22-fold and 5-fold activation of currents by UTP, respectively. Taken together, this study shows that there are different interactions between the subtypes of P2Y purinergic receptors and different Ca(2+)-activated K+ channels.
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Affiliation(s)
- Susanne E Hede
- Institute of Molecular Biology and Physiology, The August Krogh Building, University of Copenhagen, Universitetsparken 13, 2100, Copenhagen Ø, Denmark
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40
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Abstract
In many species the pancreatic duct epithelium secretes HCO3- ions at a concentration of around 140 mM by a mechanism that is only partially understood. We know that HCO3- uptake at the basolateral membrane is achieved by Na+-HCO3- cotransport and also by a H+-ATPase and Na+/H+ exchanger operating together with carbonic anhydrase. At the apical membrane, the secretion of moderate concentrations of HCO3- can be explained by the parallel activity of a Cl-/HCO3- exchanger and a Cl- conductance, either the cystic fibrosis transmembrane conductance regulator (CFTR) or a Ca2+-activated Cl- channel (CaCC). However, the sustained secretion of HCO3- into a HCO- -rich luminal fluid cannot be explained by conventional Cl-/HCO3- exchange. HCO3- efflux across the apical membrane is an electrogenic process that is facilitated by the depletion of intracellular Cl-, but it remains to be seen whether it is mediated predominantly by CFTR or by an electrogenic SLC26 anion exchanger.
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Affiliation(s)
- Martin C Steward
- Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom.
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Kittel A, Pelletier J, Bigonnesse F, Guckelberger O, Kordás K, Braun N, Robson SC, Sévigny J. Localization of nucleoside triphosphate diphosphohydrolase-1 (NTPDase1) and NTPDase2 in pancreas and salivary gland. J Histochem Cytochem 2004; 52:861-71. [PMID: 15208353 DOI: 10.1369/jhc.3a6167.2004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ectonucleoside triphosphate diphosphohydrolases (NTPDases) are membrane-bound ectoenzymes that hydrolyze extracellular nucleotides. We investigated the distribution of NTPDase1 and NTPDase2 in murine salivary gland and pancreas. Histochemistry and immunostaining (by both light and electron microscopy), combined with functional assays, were used to describe the localization patterns and enzyme activities in the organs of wild-type and NTPDase1/cd39-null mice. Pancreatic acinar cells and salivary gland acinar/myoepithelial cells were positive for NTPDase1 and NTPDase2. Ecto-ATPase activity was slightly higher in salivary glands. Ductal epithelial cells expressed ecto-ATPase activity but NTPDase1 and NTPDase2 expression were weak at best. ATPase activity was found in blood vessels of both tissues and its localization pattern overlapped with NTPDase1 staining. In these structures, NTPDase2 antibodies stained the basolateral aspect of endothelial cells and the supporting cells. Biochemical assays and histochemical staining showed relatively high levels of ATPase activity in both glands of cd39(-/-) mice. Our data therefore support a physiological role for NTPDase2 and other ectonucleotidases in the pancreas and salivary glands. Because NTPDase1 is expressed in non-vascular cell types, this finding suggests that NTPDase1 may have functions in the gastrointestinal tract that differ from those demonstrated in the vascular system.
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Affiliation(s)
- Agnes Kittel
- Department of Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, PO Box 67, 1450 Budapest, Hungary.
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Kordás KS, Sperlágh B, Tihanyi T, Topa L, Steward MC, Varga G, Kittel A. ATP and ATPase secretion by exocrine pancreas in rat, guinea pig, and human. Pancreas 2004; 29:53-60. [PMID: 15211112 DOI: 10.1097/00006676-200407000-00056] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
ATP is an extracellular regulator in numerous physiological and pathologic processes. Recently, 7 different subtypes of purinoceptors were identified on either the basolateral or the luminal membrane of pancreatic duct cells. However, the in vivo regulatory role of ATP in pancreatic function has not been established. We investigated the possible regulatory role of endogenous ATP in pancreatic function by measuring ATP concentrations and ATPase activity in pancreatic juice obtained from anesthetized rats and guinea pigs and from human patients undergoing endoscopy. Juice was collected from the main pancreatic duct in rats and guinea pigs under basal conditions or during stimulation with CCK, bombesin, or secretin. In guinea pigs, CCK, bombesin, and secretin did not affect ATP output, although they did stimulate fluid secretion. ATPase activity in the juice was evaluated by measuring the rate of hydrolysis of added ATP. Consistent with the low ATP concentrations in rat pancreatic juice, we found high levels of ATPase activity in this species. This was confirmed by HPLC, which also showed the metabolites of ATP hydrolysis. Ecto-ATPase activity was demonstrated by enzyme histochemistry in both the pancreatic acini and ducts in rats, but it was not detectable in guinea pigs and humans. These differences in ATP levels and ATPase expression may indicate significant species differences in the purinergic regulation of pancreatic secretion.
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Affiliation(s)
- Krisztina Sz Kordás
- Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary
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43
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Ryten M, Yang SY, Dunn PM, Goldspink G, Burnstock G. Purinoceptor expression in regenerating skeletal muscle in the mdx mouse model of muscular dystrophy and in satellite cell cultures. FASEB J 2004; 18:1404-6. [PMID: 15231720 DOI: 10.1096/fj.03-1175fje] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
ATP is an important extracellular signaling molecule mediating its effects by activation of P2X and P2Y receptors. P2 receptors are expressed during muscle development, and recent findings demonstrate that ATP can regulate myoblast proliferation and differentiation in vitro. However, the role of purinergic signaling during regeneration of injured skeletal muscle has not been investigated. To examine this process in a clinically relevant system, we used the mouse model of muscular dystrophy (mdx), in which muscle degeneration is rapidly followed by regeneration. The latter process, in vivo muscle regeneration, was the focus of this study, and to study the cellular mechanisms involved in it, a parallel study on normal rat skeletal myoblast cultures was conducted. Using immunohistochemistry, RT-PCR, and electrophysiology, we investigated the expression of the P2X1-7 receptor subtypes and the P2Y1,2,4,6 receptors. Experiments in vitro and in vivo demonstrated the sequential expression of the P2X5, P2Y1, and P2X2 receptors during the process of muscle regeneration. The P2X5 and P2Y1 receptors were expressed first on activated satellite cells, and the P2Y1 receptor was also expressed on infiltrating immune cells. Subsequent P2X2 receptor expression on newly formed myotubes showed significant colocalization with AChRs, suggesting a role in regulation of muscle innervation. Thus, this study provides the first evidence for a role for purinergic signaling in muscle regeneration and raises the possibility of new therapeutic strategies in the treatment of muscle disease.
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MESH Headings
- Adenosine Triphosphate/metabolism
- Animals
- Cells, Cultured
- Disease Models, Animal
- Mice
- Mice, Inbred mdx
- Muscle, Skeletal/growth & development
- Muscle, Skeletal/metabolism
- Muscular Dystrophies/metabolism
- Myoblasts/metabolism
- Rats
- Receptors, Cholinergic/metabolism
- Receptors, Purinergic P2/metabolism
- Receptors, Purinergic P2X2
- Receptors, Purinergic P2X5
- Receptors, Purinergic P2Y1
- Regeneration
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Affiliation(s)
- Mina Ryten
- Autonomic Neuroscience Institute, Royal Free & University College Medical School, Royal Free Campus, London, UK
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44
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Fronius M, Berk A, Clauss W, Schnizler M. Ion transport across Xenopus alveolar epithelium is regulated by extracellular ATP, UTP and adenosine. Respir Physiol Neurobiol 2004; 139:133-44. [PMID: 15122997 DOI: 10.1016/j.resp.2003.09.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/23/2003] [Indexed: 11/26/2022]
Abstract
Native alveolar epithelium from Xenopus lung was used for electrophysiological Ussing chamber experiments to investigate ion transport regulation. The tissue exhibits a considerable absorption of Na(+) ions and this transepithelial transport is largely up-regulated after treatment of donor animals with ACTH. Extracellular ATP, UTP and adenosine were tested for their regulating effects and all three increased I(sc), which was mainly due to a stimulation of amiloride sensitive Na(+) transport (increase of I(ami) 32% for ATP, 21% for UTP, 25% for adenosine). Solely the effect of UTP was completely abolished in the presence of amiloride. In contrast, the effects of ATP or adenosine disappeared under Cl(-)-free conditions. ATP and UTP proved to have additive effects and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), an antagonist of purinergic receptors, inhibited selectively the effect of UTP on I(sc). Further, I(sc) was increased by the P2X selective agonist beta,gamma-meATP. We were able to demonstrate, that extracellular purines and pyrimidines play a possible role as auto/paracrine messengers for alveolar ion transport regulation in Xenopus lung.
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Affiliation(s)
- Martin Fronius
- Institute of Animal Physiology, Justus-Liebig-University Giessen, Wartweg 95, D-35392 Giessen, Germany.
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45
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Bucheimer RE, Linden J. Purinergic regulation of epithelial transport. J Physiol 2004; 555:311-21. [PMID: 14694149 PMCID: PMC1664845 DOI: 10.1113/jphysiol.2003.056697] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2003] [Accepted: 12/23/2003] [Indexed: 01/12/2023] Open
Abstract
Purinergic receptors are a family of ubiquitous transmembrane receptors comprising two classes, P1 and P2 receptors, which are activated by adenosine and extracellular nucleotides (i.e. ATP, ADP, UTP and UDP), respectively. These receptors play a significant role in regulating ion transport in epithelial tissues through a variety of intracellular signalling pathways. Activation of these receptors is partially dependent on ATP (or UTP) release from cells and its subsequent metabolism, and this release can be triggered by a number of stimuli, often in the setting of cellular damage. The function of P2Y receptor stimulation is primarily via signalling through the G(q)/PLC-beta pathway and subsequent activation of Ca(2+)-dependent ion channels. P1 signalling is complex, with each of the four P1 receptors A(1), A(2A), A(2B), and A(3) having a unique role in different epithelial tissue types. In colonic epithelium the A(2B) receptor plays a prominent role in regulating Cl(-) and water secretion. In airway epithelium, A(2B) and A(1) receptors are implicated in the control of Cl(-) and other currents. In the renal tubular epithelium, A(1), A(2A), and A(3) receptors have all been identified as playing a role in controlling the ionic composition of the lumenal fluid. Here we discuss the intracellular signalling pathways for each of these receptors in various epithelial tissues and their roles in pathophysiological conditions such as cystic fibrosis.
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Affiliation(s)
- R Elaine Bucheimer
- Cardiovascular Research Center, University of Virginia, PO Box 801394, MR5 Room 1214, Charlottesville, VA 22908, USA
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46
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Burnstock G, Knight GE. Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 240:31-304. [PMID: 15548415 DOI: 10.1016/s0074-7696(04)40002-3] [Citation(s) in RCA: 581] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.
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Affiliation(s)
- Geoffrey Burnstock
- Autonomic Neuroscience Institute, Royal Free and University College Medical School, London NW3 2PF, United Kingdom
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Li Q, Luo X, Zeng W, Muallem S. Cell-specific behavior of P2X7 receptors in mouse parotid acinar and duct cells. J Biol Chem 2003; 278:47554-61. [PMID: 12968021 DOI: 10.1074/jbc.m308306200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
P2X7 receptors (P2X7Rs) affect many epithelial cell functions including transcellular ion transport, secretion, and cell death. Here we used parotid acinar and duct cells to reveal the unique cell-specific assembly and gating of the P2X7R channels. Immunolocalization indicated expression of P2X7Rs in the luminal membrane of both cell types. Stimulation with 5 mm ATP raised [Ca2+]i levels in a cell-specific manner and activated multiple currents. The current mediated by P2X7R was isolated by infusing the cells with high [EGTA]. The initial activation of acinar cell P2X7Rs by ATP was slow requiring approximately 2.5 min. Subsequent removal and addition of ATP, however, resulted in rapid inhibition and activation (gating) of the P2X7Rs. By contrast, P2X7Rs in duct cells displayed only rapid gating by ATP. Activation of P2X7Rs in both cell types was verified by (a) low Km for ATP, (b) sensitivity to external divalent ions, (c) lack of desensitization/inactivation, (d) permeability to Na+, and (e) inhibition by Brilliant Blue G, Cu2+, and pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid tetrasodium. The slow P2X7R activation in acinar cells was not affected by manipulation of exo-/endocytosis. Rather, disassembly or solidification of the actin cytoskeleton prior to incubation with ATP prevented channel assembly. Remarkably, after completion of the slow activation, manipulation of the actin cytoskeleton no longer affected gating by ATP. Accordingly, manipulation of the actin cytoskeleton had no effect on P2X7R gating by ATP in duct cells. We concluded that P2X7Rs are not active in resting acinar cells. On exposure to ATP, P2X7Rs are assembled into functional channels with the aid of the actin cytoskeleton. Once assembled, P2X7Rs are subject to rapid gating by ATP. Duct cell P2X7Rs are preassembled and therefore continually subject to rapid gating by ATP. This cell-specific behavior may reflect the specific function of P2X7Rs in the two cell types.
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Affiliation(s)
- Qin Li
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA
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Sørensen CE, Amstrup J, Rasmussen HN, Ankorina-Stark I, Novak I. Rat pancreas secretes particulate ecto-nucleotidase CD39. J Physiol 2003; 551:881-92. [PMID: 12832497 PMCID: PMC2343304 DOI: 10.1113/jphysiol.2003.049411] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 06/17/2003] [Accepted: 06/26/2003] [Indexed: 11/08/2022] Open
Abstract
In exocrine pancreas, acini release ATP and the excurrent ducts express several types of purinergic P2 receptors. Thereby, ATP, or its hydrolytic products, might play a role as a paracrine regulator between acini and ducts. The aim of the present study was to elucidate whether this acinar-ductal signalling is regulated by nucleotidase(s), and to characterize and localize one of the nucleotidases within the rat pancreas. Using RT-PCR and Western blotting we show that pancreas expresses the full length ecto-nucleoside triphosphate diphosphohydrolase, CD39. Immunofluorescence shows CD39 localization on basolateral membranes of acini and intracellularly. In small intercalated/ interlobular ducts, CD39 immunofluorescence was localized on the luminal membranes, while in larger ducts it was localized on the basolateral membranes. Upon stimulation with cholecystokinin-octapeptide-8 (CCK-8), acinar CD39 relocalizes in clusters towards the lumen and is secreted. As a result, pancreatic juice collected from intact pancreas stimulated with CCK-8 contained nucleotidase activity, including that of CD39, and no detectable amounts of ATP. Anti-CD39 antibodies detected the full length (78 kDa) CD39 in pancreatic juice. This CD39 was confined only to the particulate and not to the soluble fraction of CCK-8-stimulated secretion. No CD39 activity was detected in secretion stimulated by secretin. The role of secreted particulate, possibly microsomal, CD39 would be to regulate intraluminal ATP concentrations within the ductal tree. In conclusion, we show a novel inducible release of full length particulate CD39, and propose its role in the physiological context of pancreatic secretion.
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Affiliation(s)
- Christiane E Sørensen
- August Krogh Institute, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark
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Amstrup J, Novak I. P2X7 receptor activates extracellular signal-regulated kinases ERK1 and ERK2 independently of Ca2+ influx. Biochem J 2003; 374:51-61. [PMID: 12747800 PMCID: PMC1223572 DOI: 10.1042/bj20030585] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2003] [Accepted: 05/15/2003] [Indexed: 12/24/2022]
Abstract
P2X7 nucleotide receptors modulate a spectrum of cellular events in various cells including epithelia, such as exocrine pancreas. Although the pharmacology and channel properties of the P2X7 receptors have been studied intensively, signal transduction pathways are relatively unknown. In this study we applied a heterologous expression system of rat P2X7 receptors in HEK-293 cells. We followed the receptor expression and function using the enhanced green fluorescent protein (EGFP) tag, activation of intracellular proteins and increases in cellular Ca2+. EGFP-P2X7 receptors localized to the plasma membrane, clusters within the membrane and intracellularly. Stimulation of P2X7 receptors in HEK-293 cells led to an activation of extracellular signal-regulated kinases ERK1 and ERK2 and this activation was seen after just 1 min of stimulation with ATP. Using C- and N-terminal P2X7-receptor mutants we show that the N-terminus is important in activation of ERKs, whereas deletion of the last 230 amino acids in the C-terminus did not effect ERK activation. On the other hand, Ca2+ entry was impaired in C-terminal but not in N-terminal mutants. In cell suspensions prepared from rat pancreas we show that P2X7 receptors also activate ERK1 and ERK2, indicating that these signalling pathways are also turned on in native epithelium.
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Affiliation(s)
- Jan Amstrup
- August Krogh Institute, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen, Denmark.
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Coutinho-Silva R, Parsons M, Robson T, Lincoln J, Burnstock G. P2X and P2Y purinoceptor expression in pancreas from streptozotocin-diabetic rats. Mol Cell Endocrinol 2003; 204:141-54. [PMID: 12850289 DOI: 10.1016/s0303-7207(03)00003-0] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The expression of the nucleotide receptors P2X1, P2X2, P2X7, P2Y1, P2Y2 and P2Y4, in the pancreas of the streptozotocin-induced diabetic rat was investigated using immunohistochemistry. In diabetic animals, P2X7 receptor expression, normally located in the outer periphery of the islet, was increased and located inside the islet. Double-labelling experiments, using antibodies raised against insulin, somatostatin and glucagon, showed, for the first time, an increase in immunostaining for P2X7 receptors on islet glucagon-containing alpha cells (which had migrated to the interior), while no P2X7 receptors were found in beta and delta cells. P2Y1 receptors were present in intra-islet capillaries, while P2Y4 receptors were found on both alpha and beta cells. P2Y1 and P2Y2 receptor expression was also found in pancreatic duct cells and P2X1, P2X2, P2Y1 and P2Y2 receptors were identified in small blood vessels.
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Affiliation(s)
- Robson Coutinho-Silva
- Autonomic Neuroscience Institute, Royal Free and University College London Medical School, Rowland Hill Street, London NW3 2PF, UK.
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