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Kashlan OB, Wang XP, Sheng S, Kleyman TR. Epithelial Na + Channels Function as Extracellular Sensors. Compr Physiol 2024; 14:1-41. [PMID: 39109974 PMCID: PMC11309579 DOI: 10.1002/cphy.c230015] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2024]
Abstract
The epithelial Na + channel (ENaC) resides on the apical surfaces of specific epithelia in vertebrates and plays a critical role in extracellular fluid homeostasis. Evidence that ENaC senses the external environment emerged well before the molecular identity of the channel was reported three decades ago. This article discusses progress toward elucidating the mechanisms through which specific external factors regulate ENaC function, highlighting insights gained from structural studies of ENaC and related family members. It also reviews our understanding of the role of ENaC regulation by the extracellular environment in physiology and disease. After familiarizing the reader with the channel's physiological roles and structure, we describe the central role protein allostery plays in ENaC's sensitivity to the external environment. We then discuss each of the extracellular factors that directly regulate the channel: proteases, cations and anions, shear stress, and other regulators specific to particular extracellular compartments. For each regulator, we discuss the initial observations that led to discovery, studies investigating molecular mechanism, and the physiological and pathophysiological implications of regulation. © 2024 American Physiological Society. Compr Physiol 14:5407-5447, 2024.
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Affiliation(s)
- Ossama B. Kashlan
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Computational and Systems Biology, University
of Pittsburgh, Pittsburgh, Pennsylvania
| | - Xue-Ping Wang
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Shaohu Sheng
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Thomas R. Kleyman
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Cell Biology, University of Pittsburgh,
Pittsburgh, Pennsylvania
- Department of Pharmacology and Chemical Biology, University
of Pittsburgh, Pittsburgh, Pennsylvania
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2
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Palmer LG. Directing two-way traffic in the kidney: A tale of two ions. J Gen Physiol 2022; 154:213433. [PMID: 36048011 PMCID: PMC9437110 DOI: 10.1085/jgp.202213179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The kidneys regulate levels of Na+ and K+ in the body by varying urinary excretion of the electrolytes. Since transport of each of the two ions can affect the other, controlling both at the same time is a complex task. The kidneys meet this challenge in two ways. Some tubular segments change the coupling between Na+ and K+ transport. In addition, transport of Na+ can shift between segments where it is coupled to K+ reabsorption and segments where it is coupled to K+ secretion. This permits the kidney to maintain electrolyte balance with large variations in dietary intake.
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Affiliation(s)
- Lawrence G. Palmer
- Department of Physiology and Biophysics, Weill-Cornell Medical College, New York, NY,Correspondence to Lawrence G. Palmer:
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3
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Abstract
The Epithelial Na+ Channel, ENaC, comprised of 3 subunits (αβγ, or sometimes δβγENaC), plays a critical role in regulating salt and fluid homeostasis in the body. It regulates fluid reabsorption into the blood stream from the kidney to control blood volume and pressure, fluid absorption in the lung to control alveolar fluid clearance at birth and maintenance of normal airway surface liquid throughout life, and fluid absorption in the distal colon and other epithelial tissues. Moreover, recent studies have also revealed a role for sodium movement via ENaC in nonepithelial cells/tissues, such as endothelial cells in blood vessels and neurons. Over the past 25 years, major advances have been made in our understanding of ENaC structure, function, regulation, and role in human disease. These include the recently solved three-dimensional structure of ENaC, ENaC function in various tissues, and mutations in ENaC that cause a hereditary form of hypertension (Liddle syndrome), salt-wasting hypotension (PHA1), or polymorphism in ENaC that contributes to other diseases (such as cystic fibrosis). Moreover, great strides have been made in deciphering the regulation of ENaC by hormones (e.g., the mineralocorticoid aldosterone, glucocorticoids, vasopressin), ions (e.g., Na+ ), proteins (e.g., the ubiquitin-protein ligase NEDD4-2, the kinases SGK1, AKT, AMPK, WNKs & mTORC2, and proteases), and posttranslational modifications [e.g., (de)ubiquitylation, glycosylation, phosphorylation, acetylation, palmitoylation]. Characterization of ENaC structure, function, regulation, and role in human disease, including using animal models, are described in this article, with a special emphasis on recent advances in the field. © 2021 American Physiological Society. Compr Physiol 11:1-29, 2021.
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Affiliation(s)
- Daniela Rotin
- The Hospital for Sick Children, and The University of Toronto, Toronto, Canada
| | - Olivier Staub
- Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
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4
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Okada A, Yamana H, Morita K, Sato Y, Yamaguchi S, Kurakawa KI, Michihata N, Matsui H, Fushimi K, Nangaku M, Yamauchi T, Yasunaga H, Kadowaki T. Potassium Concentration in Initial Fluid Therapy and In-Hospital Mortality of Patients with Diabetic Ketoacidosis. J Clin Endocrinol Metab 2021; 106:e2162-e2175. [PMID: 33493293 DOI: 10.1210/clinem/dgab029] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/07/2020] [Indexed: 11/19/2022]
Abstract
CONTEXT Guidelines worldwide recommend potassium replacement of 10 to 40 mmol/L in the initial fluid therapy for patients with diabetic ketoacidosis. However, evidence is lacking as to the association between infused potassium concentration and mortality. OBJECTIVE We aimed to determine the association between infused potassium concentration and in-hospital mortality. METHODS Using the Japanese Diagnosis Procedure Combination database, we retrospectively identified inpatients admitted for treatment of diabetic ketoacidosis from July 2010 to March 2018. Patients with kidney dysfunction or serum potassium abnormalities were excluded. We evaluated the association of the potassium concentration in the total infused solutions in the first 2 days of hospitalization with 28-day in-hospital mortality using multivariable regression analysis with a cubic spline model. We also assessed the association between potassium concentration and occurrence of hyperkalemia. RESULTS We identified 14 216 patients with diabetic ketoacidosis and observed 261 deaths. The quartile cut-points for potassium concentration were 7.7, 11.4, and 16.1 mmol/L. Within the range of approximately 10 to 40 mmol/L, potassium concentration was not associated with occurrence of hyperkalemia or death. Lower potassium concentrations were associated with higher 28-day in-hospital mortality; the odds ratio for patients receiving 8 mmol/L was 1.69 (95% CI, 1.03 to 2.78; reference: 20 mmol/L), and the odds ratio increased monotonically as potassium concentration decreased further. CONCLUSION Patients receiving potassium replacement at concentrations of 10 to 40 mmol/L had similar in-hospital mortality rates, whereas lower concentrations were associated with higher mortality.
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Affiliation(s)
- Akira Okada
- Department of Prevention of Diabetes and Lifestyle-Related Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Hayato Yamana
- Department of Health Services Research, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Kojiro Morita
- Department of Health Services Research, University of Tsukuba, Tsukuba, Japan
| | - Yukihito Sato
- Department of Clinical Epidemiology and Health Economics, The University of Tokyo, Tokyo, Japan
| | - Satoko Yamaguchi
- Department of Prevention of Diabetes and Lifestyle-Related Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Kayo Ikeda Kurakawa
- Department of Prevention of Diabetes and Lifestyle-Related Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Nobuaki Michihata
- Department of Health Services Research, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Hiroki Matsui
- Department of Clinical Epidemiology and Health Economics, The University of Tokyo, Tokyo, Japan
| | - Kiyohide Fushimi
- Department of Health Policy and Informatics, Tokyo Medical and Dental University, Tokyo, Japan
| | - Masaomi Nangaku
- Division of Nephrology and Endocrinology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Toshimasa Yamauchi
- Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Hideo Yasunaga
- Department of Clinical Epidemiology and Health Economics, The University of Tokyo, Tokyo, Japan
| | - Takashi Kadowaki
- Department of Prevention of Diabetes and Lifestyle-Related Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
- Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
- Toranomon Hospital, Tokyo, Japan
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5
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Ware AW, Rasulov SR, Cheung TT, Lott JS, McDonald FJ. Membrane trafficking pathways regulating the epithelial Na + channel. Am J Physiol Renal Physiol 2019; 318:F1-F13. [PMID: 31657249 DOI: 10.1152/ajprenal.00277.2019] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Renal Na+ reabsorption, facilitated by the epithelial Na+ channel (ENaC), is subject to multiple forms of control to ensure optimal body blood volume and pressure through altering both the ENaC population and activity at the cell surface. Here, the focus is on regulating the number of ENaCs present in the apical membrane domain through pathways of ENaC synthesis and targeting to the apical membrane as well as ENaC removal, recycling, and degradation. Finally, the mechanisms by which ENaC trafficking pathways are regulated are summarized.
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Affiliation(s)
- Adam W Ware
- Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Sahib R Rasulov
- Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Tanya T Cheung
- Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - J Shaun Lott
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Fiona J McDonald
- Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
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6
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Abstract
Recent studies have suggested that postprandial increases in insulin directly contribute to reduced urinary sodium excretion. An abundance of research supports the ability of insulin to augment epithelial sodium channel (ENaC) transport. This study hypothesized that ENaC contributes to the increase in renal sodium reabsorption following a meal. To test this, we used fasted or 4 hour postprandial Sprague Dawley rats to analyze ENaC expression and activity. We also assessed total expression of additional sodium transporters (Na+-Cl− cotransporter (NCC), Na+-K+-2Cl− cotransporter (NKCC2), and Na+-K+-ATPase (NKA)) and circulating hormones involved in the renin-angiotensin-aldosterone system (RAAS). We found that after carbohydrate stimulus, ENaC open probability increased in split-open isolated collecting duct tubules, while ENaC protein levels remained unchanged. This was supported by a lack of change in phosphorylated Nedd4-2, an E3 ubiquitin ligase protein which regulates the number of ENaCs at the plasma membrane. Additionally, we found no differences in total expression of NCC, NKCC2, or NKA in the postprandial rats. Lastly, there were no significant changes in RAAS signaling between the stimulated and fasted rats, suggesting that acute hyperinsulinemia increases ENaC activity independent of the RAAS signaling cascade. These results demonstrate that insulin regulation of ENaC is a potential mechanism to preserve sodium and volume loss following a meal, and that this regulation is distinct from classical ENaC regulation by RAAS.
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7
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Wolfsdorf JI, Glaser N, Agus M, Fritsch M, Hanas R, Rewers A, Sperling MA, Codner E. ISPAD Clinical Practice Consensus Guidelines 2018: Diabetic ketoacidosis and the hyperglycemic hyperosmolar state. Pediatr Diabetes 2018; 19 Suppl 27:155-177. [PMID: 29900641 DOI: 10.1111/pedi.12701] [Citation(s) in RCA: 364] [Impact Index Per Article: 60.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Accepted: 05/31/2018] [Indexed: 12/22/2022] Open
Affiliation(s)
- Joseph I Wolfsdorf
- Division of Endocrinology, Boston Children's Hospital, Boston, Massachusetts
| | - Nicole Glaser
- Department of Pediatrics, Section of Endocrinology, University of California, Davis School of Medicine, Sacramento, California
| | - Michael Agus
- Division of Endocrinology, Boston Children's Hospital, Boston, Massachusetts.,Division of Critical Care Medicine, Boston Children's Hospital, Boston, Massachusetts
| | - Maria Fritsch
- Department of Pediatric and Adolescent Medicine, Medical University of Vienna, Vienna, Austria
| | - Ragnar Hanas
- Department of Pediatrics, NU Hospital Group, Uddevalla and Sahlgrenska Academy, Gothenburg University, Uddevalla, Sweden
| | - Arleta Rewers
- Department of Pediatrics, School of Medicine, University of Colorado, Aurora, Colorado
| | - Mark A Sperling
- Division of Endocrinology, Diabetes and Metabolism, Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Ethel Codner
- Institute of Maternal and Child Research, School of Medicine, University of Chile, Santiago, Chile
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8
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Irsik DL, Brands MW. Physiological hyperinsulinemia caused by acute hyperglycemia minimizes renal sodium loss by direct action on kidneys. Am J Physiol Regul Integr Comp Physiol 2018; 315:R547-R552. [PMID: 29791205 DOI: 10.1152/ajpregu.00016.2018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study used acute, renal artery insulin infusion in conscious rats to test the hypothesis that hyperinsulinemia attenuates glucose-induced natriuresis by a direct renal mechanism. We reported previously that hyperinsulinemia was required to prevent ad libitum eating or an acute glucose bolus from causing excessive renal sodium loss. Rats were instrumented with renal artery, aortic, and femoral vein catheters and Data Sciences International blood pressure telemeters and were housed in metabolic cages. Insulin was clamped chronically at normal levels in two groups [vehicle infused (irV) and insulin infused (irI)] by administering streptozotocin and then infusing insulin intravenously 24 h/day to maintain normal blood glucose. Bolus glucose administration was used as a meal substitute to produce hyperglycemia that was not different between groups, and urinary sodium excretion (UNaV) was measured over the next 4 h. In the irV and control (C) rats, vehicle was infused in the renal artery during that period, whereas insulin was infused in the renal artery of the irI rats. Plasma insulin increased significantly in C rats but not in either of the clamped groups. UNaV in the irV rats, which could not increase circulating insulin levels, was approximately threefold greater than in C rats, similar to our previous report. However, allowing the kidney of irI rats to experience hyperinsulinemia via the renal artery insulin infusion completely prevented this, with no blood pressure differences. These data support our hypothesis that meal-induced increases in plasma insulin are a major component of normal sodium homeostasis, and that this occurs by direct action of insulin on the kidney.
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Affiliation(s)
- Debra L Irsik
- Department of Physiology, Medical College of Georgia, Augusta University , Augusta, Georgia
| | - Michael W Brands
- Department of Physiology, Medical College of Georgia, Augusta University , Augusta, Georgia
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9
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Nizar JM, Bouby N, Bankir L, Bhalla V. Improved protocols for the study of urinary electrolyte excretion and blood pressure in rodents: use of gel food and stepwise changes in diet composition. Am J Physiol Renal Physiol 2018; 314:F1129-F1137. [PMID: 29357416 PMCID: PMC6032076 DOI: 10.1152/ajprenal.00474.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Revised: 12/28/2017] [Accepted: 12/31/2017] [Indexed: 11/22/2022] Open
Abstract
Many experimental protocols in rodents require the comparison of groups that are fed different diets. Changes in dietary electrolyte and/or fat content can influence food intake, which can potentially introduce bias or confound the results. Unpalatable diets slow growth or cause weight loss, which is exacerbated by housing the animals in individual metabolic cages or by surgery. For balance studies in mice, small changes in body weight and food intake and low urinary flow can amplify these challenges. Powder food can be administered as gel with the addition of a desired amount of water, electrolytes, drugs (if any), and a small amount of agar. We describe here how the use of gel food to vary water, Na, K, and fat content can reduce weight loss and improve reproducibility of intake, urinary excretion, and blood pressure in rodents. In addition, mild food restriction reduces the interindividual variability and intergroup differences in food intake and associated variables, thus improving the statistical power of an experiment. Finally, we also demonstrate the advantages of using gel food for weight-based drug dosing. These protocols can improve the accuracy and reproducibility of experimental data where dietary manipulations are needed and are especially advisable in rodent studies related to water balance, obesity, and blood pressure.
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Affiliation(s)
- Jonathan M Nizar
- Department of Medicine, Division of Nephrology, Stanford University School of Medicine , Palo Alto, California
| | - Nadine Bouby
- Institut National de la Santé et de la Recherche Médicale, UMRS 1138, Centre de Recherché des Cordeliers , Paris , France
- Université Pierre et Marie Curie , Paris , France
| | - Lise Bankir
- Institut National de la Santé et de la Recherche Médicale, UMRS 1138, Centre de Recherché des Cordeliers , Paris , France
- Université Pierre et Marie Curie , Paris , France
| | - Vivek Bhalla
- Department of Medicine, Division of Nephrology, Stanford University School of Medicine , Palo Alto, California
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10
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Harvey BJ, Thomas W. Aldosterone-induced protein kinase signalling and the control of electrolyte balance. Steroids 2018; 133:67-74. [PMID: 29079406 DOI: 10.1016/j.steroids.2017.10.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Revised: 10/18/2017] [Accepted: 10/21/2017] [Indexed: 01/20/2023]
Abstract
Aldosterone acts through the mineralocorticoid receptor (MR) to modulate gene expression in target tissues. In the kidney, the principal action of aldosterone is to promote sodium conservation in the distal nephron and so indirectly enhance water conservation under conditions of hypotension. Over the last twenty years the rapid activation of protein kinase signalling cascades by aldosterone has been described in various tissues. This review describes the integration of rapid protein kinase D signalling responses with the non-genomic actions of aldosterone and transcriptional effects of MR activation.
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Affiliation(s)
- Brian J Harvey
- Molecular Medicine Laboratories, Royal College of Surgeons in Ireland, Education Centre, Beaumont Hospital, Dublin, Ireland
| | - Warren Thomas
- Molecular Medicine Laboratories, Royal College of Surgeons in Ireland, Education Centre, Beaumont Hospital, Dublin, Ireland; Perdana University - Royal College of Surgeons in Ireland School of Medicine, Serdang, Selangor, Malaysia.
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11
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Irsik DL, Chen JK, Brands MW. Chronic renal artery insulin infusion increases mean arterial pressure in male Sprague-Dawley rats. Am J Physiol Renal Physiol 2018; 314:F81-F88. [PMID: 28971990 PMCID: PMC6048445 DOI: 10.1152/ajprenal.00374.2017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Revised: 09/13/2017] [Accepted: 09/26/2017] [Indexed: 12/31/2022] Open
Abstract
Hyperinsulinemia has been hypothesized to cause hypertension in obesity, type 2 diabetes, and metabolic syndrome through a renal mechanism. However, it has been challenging to isolate renal mechanisms in chronic experimental models due, in part, to technical difficulties. In this study, we tested the hypothesis that a renal mechanism underlies insulin hypertension. We developed a novel technique to permit continuous insulin infusion through the renal artery in conscious rats for 7 days. Mean arterial pressure increased by ~10 mmHg in rats that were infused intravenously (IV) with insulin and glucose. Renal artery doses were 20% of the intravenous doses and did not raise systemic insulin levels or cause differences in blood glucose. The increase in blood pressure was not different from the IV group. Mean arterial pressure did not change in vehicle-infused rats, and there were no differences in renal injury scoring due to the renal artery catheter. Glomerular filtration rate, plasma renin activity, and urinary sodium excretion did not differ between groups at baseline and did not change significantly with insulin infusion. Thus, by developing a novel approach for chronic, continuous renal artery insulin infusion, we provided new evidence that insulin causes hypertension in rats through actions initiated within the kidney.
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Affiliation(s)
- Debra L Irsik
- Department of Physiology, Medical College of Georgia at Augusta University , Augusta, Georgia
| | - Jian-Kang Chen
- Department of Cellular Biology & Anatomy, Medical College of Georgia at Augusta University , Augusta, Georgia
| | - Michael W Brands
- Department of Physiology, Medical College of Georgia at Augusta University , Augusta, Georgia
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12
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Irsik DL, Blazer-Yost BL, Staruschenko A, Brands MW. The normal increase in insulin after a meal may be required to prevent postprandial renal sodium and volume losses. Am J Physiol Regul Integr Comp Physiol 2017; 312:R965-R972. [PMID: 28330966 DOI: 10.1152/ajpregu.00354.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Revised: 03/15/2017] [Accepted: 03/15/2017] [Indexed: 12/22/2022]
Abstract
Despite the effects of insulinopenia in type 1 diabetes and evidence that insulin stimulates multiple renal sodium transporters, it is not known whether normal variation in plasma insulin regulates sodium homeostasis physiologically. This study tested whether the normal postprandial increase in plasma insulin significantly attenuates renal sodium and volume losses. Rats were instrumented with chronic artery and vein catheters, housed in metabolic cages, and connected to hydraulic swivels. Measurements of urine volume and sodium excretion (UNaV) over 24 h and the 4-h postprandial period were made in control (C) rats and insulin-clamped (IC) rats in which the postprandial increase in insulin was prevented. Twenty-four-hour urine volume (36 ± 3 vs. 15 ± 2 ml/day) and UNaV (3.0 ± 0.2 vs. 2.5 ± 0.2 mmol/day) were greater in the IC compared with C rats, respectively. Four hours after rats were given a gel meal, blood glucose and urine volume were greater in IC rats, but UNaV decreased. To simulate a meal while controlling blood glucose, C and IC rats received a glucose bolus that yielded peak increases in blood glucose that were not different between groups. Urine volume (9.7 ± 0.7 vs. 6.0 ± 0.8 ml/4 h) and UNaV (0.50 ± 0.08 vs. 0.20 ± 0.06 mmol/4 h) were greater in the IC vs. C rats, respectively, over the 4-h test. These data demonstrate that the normal increase in circulating insulin in response to hyperglycemia may be required to prevent excessive renal sodium and volume losses and suggest that insulin may be a physiological regulator of sodium balance.
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Affiliation(s)
- Debra L Irsik
- Department of Physiology, Medical College of Georgia, Augusta, Georgia
| | - Bonnie L Blazer-Yost
- Department of Biology, Indiana University-Purdue University Indianapolis, Indianapolis, Indiana; and
| | | | - Michael W Brands
- Department of Physiology, Medical College of Georgia, Augusta, Georgia;
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13
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Palygin O, Pochynyuk O, Staruschenko A. Role and mechanisms of regulation of the basolateral K ir 4.1/K ir 5.1K + channels in the distal tubules. Acta Physiol (Oxf) 2017; 219:260-273. [PMID: 27129733 PMCID: PMC5086442 DOI: 10.1111/apha.12703] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Revised: 01/28/2016] [Accepted: 04/28/2016] [Indexed: 12/11/2022]
Abstract
Epithelial K+ channels are essential for maintaining electrolyte and fluid homeostasis in the kidney. It is recognized that basolateral inward-rectifying K+ (Kir ) channels play an important role in the control of resting membrane potential and transepithelial voltage, thereby modulating water and electrolyte transport in the distal part of nephron and collecting duct. Monomeric Kir 4.1 (encoded by Kcnj10 gene) and heteromeric Kir 4.1/Kir 5.1 (Kir 4.1 together with Kir 5.1 (Kcnj16)) channels are abundantly expressed at the basolateral membranes of the distal convoluted tubule and the cortical collecting duct cells. Loss-of-function mutations in KCNJ10 cause EAST/SeSAME tubulopathy in humans associated with salt wasting, hypomagnesaemia, metabolic alkalosis and hypokalaemia. In contrast, mice lacking Kir 5.1 have severe renal phenotype that, apart from hypokalaemia, is the opposite of the phenotype seen in EAST/SeSAME syndrome. Experimental advances using genetic animal models provided critical insights into the physiological role of these channels in electrolyte homeostasis and the control of kidney function. Here, we discuss current knowledge about K+ channels at the basolateral membrane of the distal tubules with specific focus on the homomeric Kir 4.1 and heteromeric Kir 4.1/Kir 5.1 channels. Recently identified molecular mechanisms regulating expression and activity of these channels, such as cell acidification, dopamine, insulin and insulin-like growth factor-1, Src family protein tyrosine kinases, as well as the role of these channels in NCC-mediated transport in the distal convoluted tubules, are also described.
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Affiliation(s)
- Oleg Palygin
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
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14
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Pao AC. There and back again: insulin, ENaC, and the cortical collecting duct. Physiol Rep 2016; 4:4/10/e12809. [PMID: 27233302 PMCID: PMC4886174 DOI: 10.14814/phy2.12809] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 05/03/2016] [Indexed: 01/02/2023] Open
Abstract
Cell culture models suggest mechanisms by which insulin stimulates ENaC in the cortical collecting duct. These mechanisms still need to be tested for physiological significance in animal models of insulin resistance.![]()
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Affiliation(s)
- Alan C Pao
- Department of Medicine Stanford University, Stanford, California
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15
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Bankir L, Bouby N, Blondeau B, Crambert G. Glucagon actions on the kidney revisited: possible role in potassium homeostasis. Am J Physiol Renal Physiol 2016; 311:F469-86. [DOI: 10.1152/ajprenal.00560.2015] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 03/31/2016] [Indexed: 12/25/2022] Open
Abstract
It is now recognized that the metabolic disorders observed in diabetes are not, or not only due to the lack of insulin or insulin resistance, but also to elevated glucagon secretion. Accordingly, selective glucagon receptor antagonists are now proposed as a novel strategy for the treatment of diabetes. However, besides its metabolic actions, glucagon also influences kidney function. The glucagon receptor is expressed in the thick ascending limb, distal tubule, and collecting duct, and glucagon regulates the transepithelial transport of several solutes in these nephron segments. Moreover, it also influences solute transport in the proximal tubule, possibly by an indirect mechanism. This review summarizes the knowledge accumulated over the last 30 years about the influence of glucagon on the renal handling of electrolytes and urea. It also describes a possible novel role of glucagon in the short-term regulation of potassium homeostasis. Several original findings suggest that pancreatic α-cells may express a “potassium sensor” sensitive to changes in plasma K concentration and could respond by adapting glucagon secretion that, in turn, would regulate urinary K excretion. By their combined actions, glucagon and insulin, working in a combinatory mode, could ensure an independent regulation of both plasma glucose and plasma K concentrations. The results and hypotheses reviewed here suggest that the use of glucagon receptor antagonists for the treatment of diabetes should take into account their potential consequences on electrolyte handling by the kidney.
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Affiliation(s)
- Lise Bankir
- INSERM UMRS 1138, Centre de Recherche des Cordeliers, Paris, France
- Université Pierre et Marie Curie, Paris, France; and
| | - Nadine Bouby
- INSERM UMRS 1138, Centre de Recherche des Cordeliers, Paris, France
- Université Pierre et Marie Curie, Paris, France; and
- Université Paris-Descartes, Paris, France
| | - Bertrand Blondeau
- INSERM UMRS 1138, Centre de Recherche des Cordeliers, Paris, France
- Université Pierre et Marie Curie, Paris, France; and
| | - Gilles Crambert
- INSERM UMRS 1138, Centre de Recherche des Cordeliers, Paris, France
- Université Pierre et Marie Curie, Paris, France; and
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Briffa JF, Grinfeld E, Jenkin KA, Mathai ML, Poronnik P, McAinch AJ, Hryciw DH. Diet induced obesity in rats reduces NHE3 and Na(+) /K(+) -ATPase expression in the kidney. Clin Exp Pharmacol Physiol 2016; 42:1118-26. [PMID: 26173747 DOI: 10.1111/1440-1681.12452] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Revised: 06/25/2015] [Accepted: 07/01/2015] [Indexed: 01/25/2023]
Abstract
The consumption of a high fat diet (HFD) is associated with proteinuria and altered sodium handling and excretion, which can lead to kidney disease. In the proximal tubule, the Na(+) /H(+) Exchanger 3 (NHE3) is responsible for normal protein reabsorption and the reabsorption of approximately 70% of the renal sodium load. It is the Na(+) /K(+) -ATPase that provides the driving force for the reabsorption of sodium and its exit across the basolateral membrane. This study investigates the effects that consumption of a HFD for 12 weeks has on NHE3 and Na(+) /K(+) -ATPase expression in the kidney. Western blot analysis identified a significant reduction in NHE3 and its modulator, phosphorylated protein kinase B, in renal lysate from obese rats. In the obese rats, a reduction in NHE3 expression in the proximal tubule may impact on the acidification of endosomes which are responsible for albumin uptake, suggesting a key role for the exchanger in protein endocytosis in obesity. Western blot analysis identified a reduction in Na(+) /K(+) -ATPase which could also potentially impact on albumin uptake and sodium reabsorption. This study demonstrates that consumption of a HFD for 12 weeks reduces renal NHE3 and Na(+) /K(+) -ATPase expression, an effect that may contribute to the albuminuria associated with obesity. Furthermore the reduction in these transporters is not likely to contribute to the reduced sodium excretion in obesity. These data highlight a potential link between NHE3 and Na(+) /K(+) -ATPase in the pathophysiological changes in renal protein handling observed in obesity.
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Affiliation(s)
- J F Briffa
- Centre for Chronic Disease Prevention and Management, College of Health and Biomedicine, Victoria University, St Albans, Victoria, Australia.,Department of Physiology, The University of Melbourne, Parkville, Victoria, Australia
| | - E Grinfeld
- Centre for Chronic Disease Prevention and Management, College of Health and Biomedicine, Victoria University, St Albans, Victoria, Australia
| | - K A Jenkin
- Centre for Chronic Disease Prevention and Management, College of Health and Biomedicine, Victoria University, St Albans, Victoria, Australia
| | - M L Mathai
- Centre for Chronic Disease Prevention and Management, College of Health and Biomedicine, Victoria University, St Albans, Victoria, Australia
| | - P Poronnik
- Department of Physiology, School of Medical Sciences, The University of Sydney, Sydney, New South Wales, Australia
| | - A J McAinch
- Centre for Chronic Disease Prevention and Management, College of Health and Biomedicine, Victoria University, St Albans, Victoria, Australia
| | - D H Hryciw
- Department of Physiology, The University of Melbourne, Parkville, Victoria, Australia
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17
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Ueda Y, Ookawara S, Ito K, Miyazawa H, Kaku Y, Hoshino T, Tabei K, Morishita Y. Changes in urinary potassium excretion in patients with chronic kidney disease. Kidney Res Clin Pract 2016; 35:78-83. [PMID: 27366661 PMCID: PMC4919657 DOI: 10.1016/j.krcp.2016.02.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 01/09/2016] [Accepted: 02/03/2016] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Hyperkalemia is one of the more serious complications of chronic kidney disease (CKD), and the cause of potassium retention is a reduction in urinary potassium excretion. However, few studies have examined the extent of the decrease of urinary potassium excretion in detail with respect to decreased renal function. METHODS Nine hundred eighty-nine patients with CKD (CKD stages G1 and G2 combined: 135; G3a: 107; G3b: 170; G4: 289; and G5: 288) were evaluated retrospectively. Values for urinary potassium excretion were compared between CKD stages, and the associations between urinary potassium excretion and clinical parameters, including diabetes mellitus status and use of renin-angiotensin-aldosterone system inhibitors, were analyzed using a multivariable linear regression analysis. RESULTS Urinary potassium excretion gradually decreased with worsening of CKD (G5: 24.8 ± 0.8 mEq/d, P < 0.001 vs. earlier CKD stages). In contrast, the value of fractional excretion of potassium at CKD G5 was significantly higher than that at the other stages (30.63 ± 0.93%, P < 0.001). Multivariable linear regression analysis revealed that urinary potassium excretion was independently associated with urinary sodium excretion (standardized coefficient, 0.499), the estimated glomerular filtration rate (0.281), and serum chloride concentration (-0.086). CONCLUSION This study demonstrated that urinary potassium excretion decreased with reductions in renal function. Furthermore, urinary potassium excretion was mainly affected by urinary sodium excretion and estimated glomerular filtration rate in patients with CKD, whereas the presence of diabetes mellitus and use of renin-angiotensin-aldosterone system inhibitors were not associated with urinary potassium excretion in this study.
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Affiliation(s)
| | - Susumu Ookawara
- Division of Nephrology, First Department of Integrated Medicine, Saitama Medical Center, Jichi Medical University, Saitama, Japan
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18
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Zaika O, Tomilin V, Mamenko M, Bhalla V, Pochynyuk O. New perspective of ClC-Kb/2 Cl- channel physiology in the distal renal tubule. Am J Physiol Renal Physiol 2016; 310:F923-30. [PMID: 26792067 PMCID: PMC5002062 DOI: 10.1152/ajprenal.00577.2015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 01/14/2016] [Indexed: 12/17/2022] Open
Abstract
Since its identification as the underlying molecular cause of Bartter's syndrome type 3, ClC-Kb (ClC-K2 in rodents, henceforth it will be referred as ClC-Kb/2) is proposed to play an important role in systemic electrolyte balance and blood pressure regulation by controlling basolateral Cl(-) exit in the distal renal tubular segments from the cortical thick ascending limb to the outer medullary collecting duct. Considerable experimental and clinical effort has been devoted to the identification and characterization of disease-causing mutations as well as control of the channel by its cofactor, barttin. However, we have only begun to unravel the role of ClC-Kb/2 in different tubular segments and to reveal the regulators of its expression and function, e.g., insulin and IGF-1. In this review we discuss recent experimental evidence in this regard and highlight unexplored questions critical to understanding ClC-Kb/2 physiology in the kidney.
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Affiliation(s)
- Oleg Zaika
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas; and
| | - Viktor Tomilin
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas; and
| | - Mykola Mamenko
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas; and
| | - Vivek Bhalla
- Division of Nephrology, Department of Medicine, Stanford University, Stanford, California
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, Texas; and
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19
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Nizar JM, Dong W, McClellan RB, Labarca M, Zhou Y, Wong J, Goens DG, Zhao M, Velarde N, Bernstein D, Pellizzon M, Satlin LM, Bhalla V. Na+-sensitive elevation in blood pressure is ENaC independent in diet-induced obesity and insulin resistance. Am J Physiol Renal Physiol 2016; 310:F812-20. [PMID: 26841823 PMCID: PMC4867314 DOI: 10.1152/ajprenal.00265.2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 01/28/2016] [Indexed: 02/08/2023] Open
Abstract
The majority of patients with obesity, insulin resistance, and metabolic syndrome have hypertension, but the mechanisms of hypertension are poorly understood. In these patients, impaired sodium excretion is critical for the genesis of Na(+)-sensitive hypertension, and prior studies have proposed a role for the epithelial Na(+) channel (ENaC) in this syndrome. We characterized high fat-fed mice as a model in which to study the contribution of ENaC-mediated Na(+) reabsorption in obesity and insulin resistance. High fat-fed mice demonstrated impaired Na(+) excretion and elevated blood pressure, which was significantly higher on a high-Na(+) diet compared with low fat-fed control mice. However, high fat-fed mice had no increase in ENaC activity as measured by Na(+) transport across microperfused cortical collecting ducts, electrolyte excretion, or blood pressure. In addition, we found no difference in endogenous urinary aldosterone excretion between groups on a normal or high-Na(+) diet. High fat-fed mice provide a model of metabolic syndrome, recapitulating obesity, insulin resistance, impaired natriuresis, and a Na(+)-sensitive elevation in blood pressure. Surprisingly, in contrast to previous studies, our data demonstrate that high fat feeding of mice impairs natriuresis and produces elevated blood pressure that is independent of ENaC activity and likely caused by increased Na(+) reabsorption upstream of the aldosterone-sensitive distal nephron.
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Affiliation(s)
- Jonathan M Nizar
- Division of Nephrology, Department of Medicine, Stanford University, Palo Alto, California
| | - Wuxing Dong
- Division of Nephrology, Department of Medicine, Stanford University, Palo Alto, California
| | - Robert B McClellan
- Division of Nephrology, Department of Medicine, Stanford University, Palo Alto, California
| | - Mariana Labarca
- Division of Nephrology, Department of Medicine, Stanford University, Palo Alto, California
| | - Yuehan Zhou
- Division of Pediatric Nephrology, Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Jared Wong
- Division of Nephrology, Department of Medicine, Stanford University, Palo Alto, California
| | - Donald G Goens
- Division of Nephrology, Department of Medicine, Stanford University, Palo Alto, California
| | - Mingming Zhao
- Division of Pediatric Cardiology, Department of Pediatrics, Stanford University, Stanford, California; and
| | - Nona Velarde
- Division of Nephrology, Department of Medicine, Stanford University, Palo Alto, California
| | - Daniel Bernstein
- Division of Pediatric Cardiology, Department of Pediatrics, Stanford University, Stanford, California; and
| | | | - Lisa M Satlin
- Division of Pediatric Nephrology, Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Vivek Bhalla
- Division of Nephrology, Department of Medicine, Stanford University, Palo Alto, California;
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20
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Ecelbarger CM. Metabolic syndrome, hypertension, and the frontier between. Am J Physiol Renal Physiol 2016; 310:F1175-7. [PMID: 26911845 DOI: 10.1152/ajprenal.00095.2016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 02/22/2016] [Indexed: 12/20/2022] Open
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21
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Zaika O, Palygin O, Tomilin V, Mamenko M, Staruschenko A, Pochynyuk O. Insulin and IGF-1 activate Kir4.1/5.1 channels in cortical collecting duct principal cells to control basolateral membrane voltage. Am J Physiol Renal Physiol 2016; 310:F311-21. [PMID: 26632606 PMCID: PMC4839479 DOI: 10.1152/ajprenal.00436.2015] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 11/30/2015] [Indexed: 01/12/2023] Open
Abstract
Potassium Kir4.1/5.1 channels are abundantly expressed at the basolateral membrane of principal cells in the cortical collecting duct (CCD), where they are thought to modulate transport rates by controlling transepithelial voltage. Insulin and insulin-like growth factor-1 (IGF-1) stimulate apically localized epithelial sodium channels (ENaC) to augment sodium reabsorption in the CCD. However, little is known about their actions on potassium channels localized at the basolateral membrane. In this study, we implemented patch-clamp analysis in freshly isolated murine CCD to assess the effect of these hormones on Kir4.1/5.1 at both single channel and cellular levels. We demonstrated that K(+)-selective conductance via Kir4.1/5.1 is the major contributor to the macroscopic current recorded from the basolateral side in principal cells. Acute treatment with 10 μM amiloride (ENaC blocker), 100 nM tertiapin-Q (TPNQ; ROMK inhibitor), and 100 μM ouabain (Na(+)-K(+)-ATPase blocker) failed to produce a measurable effect on the macroscopic current. In contrast, Kir4.1 inhibitor nortriptyline (100 μM), but not fluoxetine (100 μM), virtually abolished whole cell K(+)-selective conductance. Insulin (100 nM) markedly increased the open probability of Kir4.1/5.1 and nortriptyline-sensitive whole cell current, leading to significant hyperpolarization of the basolateral membrane. Inhibition of the phosphatidylinositol 3-kinase cascade with LY294002 (20 μM) abolished action of insulin on Kir4.1/5.1. IGF-1 had similar stimulatory actions on Kir4.1/5.1-mediated conductance only when applied at a higher (500 nM) concentration and was ineffective at 100 nM. We concluded that both insulin and, to a lesser extent, IGF-1 activate Kir4.1/5.1 channel activity and open probability to hyperpolarize the basolateral membrane, thereby facilitating Na(+) reabsorption in the CCD.
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Affiliation(s)
- Oleg Zaika
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
| | - Oleg Palygin
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; and
| | - Viktor Tomilin
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas; Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russian Federation
| | - Mykola Mamenko
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
| | | | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas;
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22
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Prevalence and potential risk factors of hypokalemia in pediatric patients with diabetic ketoacidosis. INTERNATIONAL JOURNAL OF PEDIATRIC ENDOCRINOLOGY 2015. [PMCID: PMC4429100 DOI: 10.1186/1687-9856-2015-s1-p8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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23
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P2C-Type ATPases and Their Regulation. Mol Neurobiol 2015; 53:1343-1354. [DOI: 10.1007/s12035-014-9076-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Accepted: 12/29/2014] [Indexed: 12/12/2022]
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24
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Ilatovskaya DV, Levchenko V, Brands MW, Pavlov TS, Staruschenko A. Cross-talk between insulin and IGF-1 receptors in the cortical collecting duct principal cells: implication for ENaC-mediated Na+ reabsorption. Am J Physiol Renal Physiol 2015; 308:F713-9. [PMID: 25651558 DOI: 10.1152/ajprenal.00081.2014] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Accepted: 01/20/2015] [Indexed: 12/17/2022] Open
Abstract
Insulin and IGF-1 are recognized as powerful regulators of the epithelial Na+ channel (ENaC) in the aldosterone-sensitive distal nephron. As previously described, these hormones both acutely increase ENaC activity in freshly isolated split open tubules and cultured principal cortical collecting duct cells. The present study was aimed at differentiating the effects of insulin and IGF-1 on Na+ transport in immortalized mpkCCDcl4 cells and defining their interrelations. We have shown that both insulin and IGF-1 applied basolaterally, but not apically, enhanced transepithelial Na+ transport in the mpkCCDcl4 cell line with EC50 values of 8.8 and 14.5 nM, respectively. Insulin treatment evoked phosphorylation of both insulin and IGF-1 receptors, whereas the effects of IGF-1 were more profound on its own receptor rather than the insulin receptor. AG-1024 and PPP, inhibitors of IGF-1 and insulin receptor tyrosine kinase activity, diminished insulin- and IGF-1-stimulated Na+ transport in mpkCCDcl4 cells. The effects of insulin and IGF-1 on ENaC-mediated currents were found to be additive, with insulin likely stimulating both IGF-1 and insulin receptors. We hypothesize that insulin activates IGF-1 receptors in addition to its own receptors, making the effects of these hormones interconnected.
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Affiliation(s)
- Daria V Ilatovskaya
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; and
| | - Vladislav Levchenko
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; and
| | - Michael W Brands
- Department of Physiology, Georgia Regents University, Augusta, Georgia
| | - Tengis S Pavlov
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; and
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25
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Zaika O, Mamenko M, Boukelmoune N, Pochynyuk O. IGF-1 and insulin exert opposite actions on ClC-K2 activity in the cortical collecting ducts. Am J Physiol Renal Physiol 2014; 308:F39-48. [PMID: 25339702 DOI: 10.1152/ajprenal.00545.2014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Despite similar stimulatory actions on the epithelial sodium channel (ENaC)-mediated sodium reabsorption in the distal tubule, insulin promotes kaliuresis, whereas insulin-like growth factor-1 (IGF-1) causes a reduction in urinary potassium levels. The factors contributing to this phenomenon remain elusive. Electrogenic distal nephron ENaC-mediated Na(+) transport establishes driving force for Cl(-) reabsorption and K(+) secretion. Using patch-clamp electrophysiology, we document that a Cl(-) channel is highly abundant on the basolateral plasma membrane of intercalated cells in freshly isolated mouse cortical collecting duct (CCD) cells. The channel has characteristics attributable to the ClC-K2: slow gating kinetics, conductance ∼10 pS, voltage independence, Cl(-)>NO3 (-) anion selectivity, and inhibition/activation by low/high pH, respectively. IGF-1 (100 and 500 nM) acutely stimulates ClC-K2 activity in a reversible manner. Inhibition of PI3-kinase (PI3-K) with LY294002 (20 μM) abrogates activation of ClC-K2 by IGF-1. Interestingly, insulin (100 nM) reversibly decreases ClC-K2 activity in CCD cells. This inhibitory action is independent of PI3-K and is mediated by stimulation of a mitogen-activated protein kinase-dependent cascade. We propose that IGF-1, by stimulating ClC-K2 channels, promotes net Na(+) and Cl(-) reabsorption, thus reducing driving force for potassium secretion by the CCD. In contrast, inhibition of ClC-K2 by insulin favors coupling of Na(+) reabsorption with K(+) secretion at the apical membrane contributing to kaliuresis.
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Affiliation(s)
- Oleg Zaika
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
| | - Mykola Mamenko
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
| | - Nabila Boukelmoune
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
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26
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Wolfsdorf JI, Allgrove J, Craig ME, Edge J, Glaser N, Jain V, Lee WWR, Mungai LNW, Rosenbloom AL, Sperling MA, Hanas R. ISPAD Clinical Practice Consensus Guidelines 2014. Diabetic ketoacidosis and hyperglycemic hyperosmolar state. Pediatr Diabetes 2014; 15 Suppl 20:154-79. [PMID: 25041509 DOI: 10.1111/pedi.12165] [Citation(s) in RCA: 214] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Accepted: 05/21/2014] [Indexed: 12/16/2022] Open
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Roles of renal proximal tubule transport in acid/base balance and blood pressure regulation. BIOMED RESEARCH INTERNATIONAL 2014; 2014:504808. [PMID: 24982885 PMCID: PMC4058521 DOI: 10.1155/2014/504808] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 05/16/2014] [Indexed: 02/06/2023]
Abstract
Sodium-coupled bicarbonate absorption from renal proximal tubules (PTs) plays a pivotal role in the maintenance of systemic acid/base balance. Indeed, mutations in the Na+-HCO3− cotransporter NBCe1, which mediates a majority of bicarbonate exit from PTs, cause severe proximal renal tubular acidosis associated with ocular and other extrarenal abnormalities. Sodium transport in PTs also plays an important role in the regulation of blood pressure. For example, PT transport stimulation by insulin may be involved in the pathogenesis of hypertension associated with insulin resistance. Type 1 angiotensin (Ang) II receptors in PT are critical for blood pressure homeostasis. Paradoxically, the effects of Ang II on PT transport are known to be biphasic. Unlike in other species, however, Ang II is recently shown to dose-dependently stimulate human PT transport via nitric oxide/cGMP/ERK pathway, which may represent a novel therapeutic target in human hypertension. In this paper, we will review the physiological and pathophysiological roles of PT transport.
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28
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Rossier BC. Epithelial sodium channel (ENaC) and the control of blood pressure. Curr Opin Pharmacol 2014; 15:33-46. [DOI: 10.1016/j.coph.2013.11.010] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 11/18/2013] [Accepted: 11/18/2013] [Indexed: 11/29/2022]
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Abstract
A new understanding of renal potassium balance has emerged as the molecular underpinnings of potassium secretion have become illuminated, highlighting the key roles of apical potassium channels, renal outer medullary potassium channel (ROMK) and Big Potassium (BK), in the aldosterone-sensitive distal nephron and collecting duct. These channels act as the final-regulated components of the renal potassium secretory machinery. Their activity, number, and driving forces are precisely modulated to ensure potassium excretion matches dietary potassium intake. Recent identification of the underlying regulatory mechanisms at the molecular level provides a new appreciation of the physiology and reveals a molecular insight to explain the paradoxic actions of aldosterone on potassium secretion. Here, we review the current state of knowledge in the field.
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Affiliation(s)
- Paul A Welling
- Department of Physiology, University of Maryland Medical School, Baltimore, MD, USA.
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30
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Carlotti APDCP, St George-Hyslop C, Bohn D, Halperin ML. Hypokalemia during treatment of diabetic ketoacidosis: clinical evidence for an aldosterone-like action of insulin. J Pediatr 2013; 163:207-12.e1. [PMID: 23410602 DOI: 10.1016/j.jpeds.2013.01.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Revised: 12/11/2012] [Accepted: 01/03/2013] [Indexed: 10/27/2022]
Abstract
OBJECTIVES To investigate whether the development of hypokalemia in patients with diabetic ketoacidosis (DKA) treated in the pediatric critical care unit (PCCU) could be caused by increased potassium (K(+)) excretion and its association with insulin treatment. STUDY DESIGN In this prospective observational study of patients with DKA admitted to the PCCU, blood and timed urine samples were collected for measurement of sodium (Na(+)), K(+), and creatinine concentrations and for calculations of Na(+) and K(+) balances. K(+) excretion rate was expressed as urine K(+)-to-creatinine ratio and fractional excretion of K(+). RESULTS Of 31 patients, 25 (81%) developed hypokalemia (plasma K(+) concentration <3.5 mmol/L) in the PCCU at a median time of 24 hours after therapy began. At nadir plasma K(+) concentration, urine K(+)-to-creatinine ratio and fractional excretion of K(+) were greater in patients who developed hypokalemia compared with those without hypokalemia (19.8 vs 6.7, P = .04; and 31.3% vs 9.4%, P = .004, respectively). Patients in the hypokalemia group received a continuous infusion of intravenous insulin for a longer time (36.5 vs 20 hours, P = .015) and greater amount of Na(+) (19.4 vs 12.8 mmol/kg, P = .02). At peak kaliuresis, insulin dose was higher in the hypokalemia group (median 0.07, range 0-0.24 vs median 0.025, range 0-0.05 IU/kg; P = .01), and there was a significant correlation between K(+) and Na(+) excretion (r = 0.67, P < .0001). CONCLUSIONS Hypokalemia was a delayed complication of DKA treatment in the PCCU, associated with high K(+) and Na(+) excretion rates and a prolonged infusion of high doses of insulin.
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31
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Pavlov TS, Ilatovskaya DV, Levchenko V, Li L, Ecelbarger CM, Staruschenko A. Regulation of ENaC in mice lacking renal insulin receptors in the collecting duct. FASEB J 2013; 27:2723-32. [PMID: 23558339 DOI: 10.1096/fj.12-223792] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The epithelial sodium channel (ENaC) is one of the central effectors involved in regulation of salt and water homeostasis in the kidney. To study mechanisms of ENaC regulation, we generated knockout mice lacking the insulin receptor (InsR KO) specifically in the collecting duct principal cells. Single-channel analysis in freshly isolated split-open tubules demonstrated that the InsR-KO mice have significantly lower ENaC activity compared to their wild-type (C57BL/6J) littermates when animals were fed either normal or sodium-deficient diets. Immunohistochemical and Western blot assays demonstrated no significant changes in expression of ENaC subunits in InsR-KO mice compared to wild-type littermates. Insulin treatment caused greater ENaC activity in split-open tubules isolated from wild-type mice but did not have this effect in the InsR-KO mice. Thus, these results suggest that insulin increases ENaC activity via its own receptor affecting the channel open probability. To further determine the mechanism of the action of insulin on ENaC, we used mouse mpkCCDc14 principal cells. Insulin significantly augmented amiloride-sensitive transepithelial flux in these cells. Pretreatment of the mpkCCDc14 cells with phosphatidylinositol 3-kinase (LY294002; 10 μM) or mTOR (PP242; 100 nM) inhibitors precluded this effect. This study provides new information about the importance of insulin receptors expressed in collecting duct principal cells for ENaC activity.
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Affiliation(s)
- Tengis S Pavlov
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA
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32
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Li L, Garikepati RM, Tsukerman S, Kohan D, Wade JB, Tiwari S, Ecelbarger CM. Reduced ENaC activity and blood pressure in mice with genetic knockout of the insulin receptor in the renal collecting duct. Am J Physiol Renal Physiol 2012. [PMID: 23195676 DOI: 10.1152/ajprenal.00161.2012] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
To elucidate the role of the insulin receptor (IR) in collecting duct (CD), we bred mice with IR selectively deleted from CD principal cells using an aquaporin-2 promoter to drive Cre-recombinase expression. Young, adult male knockout (KO) mice had altered plasma and electrolyte homeostasis under high- (HS) and low-sodium (LS) diets, relative to wild-type (WT) littermates. One week of LS feeding led to a significant reduction in urine potassium (K(+)) and sodium (Na(+)) excretion in KO, and a reduction in the ratio of Na(+) to chloride (Cl(-)) in plasma, relative to WT. HS diet (1 wk) increased plasma K(+) and reduced urine Na(+) to Cl(-) ratio in the KO. Furthermore, KO mice had a significantly (P = 0.025) blunted natriuretic response to benzamil, an epithelial sodium channel (ENaC) antagonist. Western blotting of cortex homogenates revealed modestly, but significantly (∼15%), lower band density for the β-subunit of ENaC in the KO vs. WT mice, with no differences for the α- or γ-subunits. Moreover, blood pressure (BP), measured by radiotelemetry, was significantly lower in KO vs. WT mice under basal conditions (mmHg): 112 ± 5 (WT), 104 ± 2 (KO), P = 0.023. Chronic insulin infusion reduced heart rate in the WT, but not in the KO, and modestly reduced BP in the WT only. Overall, these results support a fundamental role for insulin through its classic receptor in the modulation of electrolyte homeostasis and BP.
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Affiliation(s)
- Lijun Li
- Department of Medicine, Georgetown University, Washington, DC 20007, USA
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