1
|
Passaglia P, Ceron CS, Mecawi AS, Antunes-Rodrigues J, Coelho EB, Tirapelli CR. Angiotensin type 1 receptor mediates chronic ethanol consumption-induced hypertension and vascular oxidative stress. Vascul Pharmacol 2015; 74:49-59. [PMID: 25872164 DOI: 10.1016/j.vph.2015.04.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 03/09/2015] [Accepted: 04/04/2015] [Indexed: 02/06/2023]
Abstract
OBJECTIVES We hypothesized that chronic ethanol intake enhances vascular oxidative stress and induces hypertension through renin-angiotensin system (RAS) activation. METHODS AND RESULTS Male Wistar rats were treated with ethanol (20% v/v). The increase in blood pressure induced by ethanol was prevented by losartan (10mg/kg/day; p.o. gavage), a selective AT1 receptor antagonist. Chronic ethanol intake increased plasma renin activity (PRA), angiotensin converting enzyme (ACE) activity, plasma angiotensin I (ANG I) and angiotensin II (ANG II) levels and serum aldosterone levels. No differences on plasma osmolality and sodium or potassium levels were detected after treatment with ethanol. Ethanol consumption did not alter ACE activity, as well as the levels of ANG I and ANG II in the rat aorta or mesenteric arterial bed (MAB). Ethanol induced systemic and vascular oxidative stress (aorta and MAB) and these effects were prevented by losartan. The decrease on plasma and vascular nitrate/nitrite (NOx) levels induced by ethanol was prevented by losartan. Ethanol intake did not alter protein expression of ACE, AT1 or AT2 receptors in both aorta and MAB. Aortas from ethanol-treated rats displayed decreased ERK1/2 phosphorylation and increased protein expression of SAPK/JNK. These responses were prevented by losartan. MAB from ethanol-treated rats displayed reduced phosphorylation of p38MAPK and ERK1/2 and losartan did not prevent these responses. CONCLUSIONS Our study provides novel evidence that chronic ethanol intake increases blood pressure, induces vascular oxidative stress and decreases nitric oxide (NO) bioavailability through AT1-dependent mechanisms.
Collapse
Affiliation(s)
- Patrícia Passaglia
- Programa de pós-graduação em Toxicologia, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo (USP), Ribeirão Preto, São Paulo, Brazil; Escola de Enfermagem de Ribeirão Preto, Laboratório de Farmacologia, USP, Ribeirão Preto, São Paulo, Brazil
| | - Carla S Ceron
- Escola de Enfermagem de Ribeirão Preto, Laboratório de Farmacologia, USP, Ribeirão Preto, São Paulo, Brazil
| | - André S Mecawi
- Faculdade de Medicina de Ribeirão Preto, USP, Ribeirão Preto, São Paulo, Brazil
| | | | - Eduardo B Coelho
- Faculdade de Medicina de Ribeirão Preto, USP, Ribeirão Preto, São Paulo, Brazil
| | - Carlos R Tirapelli
- Escola de Enfermagem de Ribeirão Preto, Laboratório de Farmacologia, USP, Ribeirão Preto, São Paulo, Brazil.
| |
Collapse
|
2
|
Salyer SA, Parks J, Barati MT, Lederer ED, Clark BJ, Klein JD, Khundmiri SJ. Aldosterone regulates Na(+), K(+) ATPase activity in human renal proximal tubule cells through mineralocorticoid receptor. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2143-52. [PMID: 23684706 DOI: 10.1016/j.bbamcr.2013.05.009] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Revised: 04/15/2013] [Accepted: 05/08/2013] [Indexed: 12/21/2022]
Abstract
The mechanisms by which aldosterone increases Na(+), K(+) ATPase and sodium channel activity in cortical collecting duct and distal nephron have been extensively studied. Recent investigations demonstrate that aldosterone increases Na-H exchanger-3 (NHE-3) activity, bicarbonate transport, and H(+) ATPase in proximal tubules. However, the role of aldosterone in regulation of Na(+), K(+) ATPase in proximal tubules is unknown. We hypothesize that aldosterone increases Na(+), K(+) ATPase activity in proximal tubules through activation of the mineralocorticoid receptor (MR). Immunohistochemistry of kidney sections from human, rat, and mouse kidneys revealed that the MR is expressed in the cytosol of tubules staining positively for Lotus tetragonolobus agglutinin and type IIa sodium-phosphate cotransporter (NpT2a), confirming proximal tubule localization. Adrenalectomy in Sprague-Dawley rats decreased expression of MR, ENaC α, Na(+), K(+) ATPase α1, and NHE-1 in all tubules, while supplementation with aldosterone restored expression of above proteins. In human kidney proximal tubule (HKC11) cells, treatment with aldosterone resulted in translocation of MR to the nucleus and phosphorylation of SGK-1. Treatment with aldosterone also increased Na(+), K(+) ATPase-mediated (86)Rb uptake and expression of Na(+), K(+) ATPase α1 subunits in HKC11 cells. The effects of aldosterone on Na(+), K(+) ATPase-mediated (86)Rb uptake were prevented by spironolactone, a competitive inhibitor of aldosterone for the MR, and partially by Mifepristone, a glucocorticoid receptor (GR) inhibitor. These results suggest that aldosterone regulates Na(+), K(+) ATPase in renal proximal tubule cells through an MR-dependent mechanism.
Collapse
Affiliation(s)
- Sarah A Salyer
- Department of Medicine, Kidney Disease Program, University of Louisville, Louisville, KY, USA
| | | | | | | | | | | | | |
Collapse
|
3
|
Sun P, Antoun J, Lin DH, Yue P, Gotlinger KH, Capdevila J, Wang WH. Cyp2c44 epoxygenase is essential for preventing the renal sodium absorption during increasing dietary potassium intake. Hypertension 2011; 59:339-47. [PMID: 22184322 DOI: 10.1161/hypertensionaha.111.178475] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The aim of this study is to test whether the Cyp2c44 epoxygenase-dependent metabolism of arachidonic acid prevents the hypertensive effect of a high K (HK) intake by inhibiting the epithelial sodium channel (ENaC) activity. A HK intake elevated Cyp2c44 mRNA expression and 11,12-epoxyeicosatrienoic acid levels in the cortical collecting duct in Cyp2c44(+/+) mice (wild-type [wt]). However, an HK intake failed to increase 11,12-epoxyeicosatrienoic acid formation in the cortical collecting ducts of Cyp2c44(-/-) mice. Moreover, increasing K intake enhanced arachidonic acid-induced inhibition of ENaC in the wt but not in Cyp2c44(-/-) mice. In contrast, 11,12-epoxyeicosatrienoic acid, a Cyp2c44 metabolite, inhibited ENaC in the wt and Cyp2c44(-/-) mice. The notion that Cyp2c44 is the epoxygenase responsible for mediating the inhibitory effects of arachidonic acid on ENaC is further suggested by the observation that inhibiting Cyp-epoxygenase increased the whole-cell Na currents in principal cells of wt but not in Cyp2c44(-/-) mice. Feeding mice with an HK diet raised the systemic blood pressures of Cyp2c44(-/-) mice but was without an effect on wt mice. Moreover, application of amiloride abolished the HK-induced hypertension in Cyp2c44(-/-) mice. The HK-induced hypertension of Cyp2c44(-/-) mice was accompanied by decreasing 24-hour urinary Na excretion and increasing the plasma Na concentration, and the effects were absent in wt mice. In contrast, disruption of the Cyp2c44 gene did not alter K excretion. We conclude that Cyp2c44 epoxygenase mediates the inhibitory effect of arachidonic acid on ENaC and that Cyp2c44 functions as an HK-inducible antihypertensive enzyme responsible for inhibiting ENaC activity and Na absorption in the aldosterone-sensitive distal nephron.
Collapse
Affiliation(s)
- Peng Sun
- Department of Pharmacology, New York Medical College, 15 Dana Rd, Valhalla, NY 10595, USA
| | | | | | | | | | | | | |
Collapse
|
4
|
Wade JB, Stanton BA, Brown D. Structural Correlates of Transport in Distal Tubule and Collecting Duct Segments. Compr Physiol 2011. [DOI: 10.1002/cphy.cp080104] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
5
|
|
6
|
Kaissling B, Kriz W. Morphology of the Loop of Henle, Distal Tubule, and Collecting Duct. Compr Physiol 2011. [DOI: 10.1002/cphy.cp080103] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
7
|
Trune DR, Kempton JB, Gross ND. Mineralocorticoid receptor mediates glucocorticoid treatment effects in the autoimmune mouse ear. Hear Res 2005; 212:22-32. [PMID: 16307853 DOI: 10.1016/j.heares.2005.10.006] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2005] [Accepted: 10/07/2005] [Indexed: 11/24/2022]
Abstract
The standard treatment for many hearing disorders is glucocorticoid therapy, although the cochlear mechanisms involved in steroid-responsive hearing loss are poorly understood. Cochlear dysfunction in autoimmune mice has recently been shown to be controlled with the mineralocorticoid aldosterone as effectively as with the glucocorticoid prednisolone. Because aldosterone regulates sodium, potassium, and other electrolyte homeostasis, this implied the restoration of hearing with the mineralocorticoid was due to its impact on cochlear ion transport, particularly in the stria vascularis. This also suggested glucocorticoids may be controlling hearing recovery in part through their binding to the mineralocorticoid receptor in addition to their glucocorticoid receptor-mediated anti-inflammatory and immunosuppressive functions. Therefore, the aim of the present study was to better delineate the role of the mineralocorticoid receptor in steroid control of hearing in the autoimmune mouse. Spironolactone, a mineralocorticoid receptor antagonist, was administered to MRL/MpJ-Fas(lpr) autoimmune mice in combination with either aldosterone or prednisolone to compare their hearing and systemic disease with mice that received either steroid alone. ABR thresholds showed either aldosterone or prednisolone alone preserved hearing in the mice, but spironolactone prevented both steroids from maintaining normal cochlear function. This suggested both steroids are preserving hearing through the mineralocorticoid receptor within the ear to regulate endolymph homeostasis. The spironolactone treatment did not block normal glucocorticoid receptor-mediated immune-suppression functions because mice receiving prednisolone, either with or without spironolactone, maintained normal body weights, hematocrits, and serum immune complexes. Thus, reducing systemic autoimmune disease was not sufficient to control hearing if mineralocorticoid receptor-mediated functions were blocked. It was concluded the inner ear mineralocorticoid receptor is a significant target of glucocorticoids and a factor that should be considered in therapeutic treatments for steroid-responsive hearing loss.
Collapse
Affiliation(s)
- Dennis R Trune
- Oregon Hearing Research Center, Department of Otolaryngology-Head and Neck Surgery; Oregon Health and Science University, Mail Code NRC04, 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA.
| | | | | |
Collapse
|
8
|
Abstract
The mammalian collecting duct plays a dominant role in regulating K(+) excretion by the nephron. The collecting duct exhibits axial and intrasegmental cell heterogeneity and is composed of at least two cell types: collecting duct cells (principal cells) and intercalated cells. Under normal circumstances, the collecting duct cell in the cortical collecting duct secretes K(+), whereas under K(+) depletion, the intercalated cell reabsorbs K(+). Assessment of the electrochemical driving forces and of membrane conductances for transcellular and paracellular electrolyte movement, the characterization of several ATPases, patch-clamp investigation, and cloning of the K(+) channel have provided important insights into the role of pumps and channels in those tubule cells that regulate K(+) secretion and reabsorption. This review summarizes K(+) transport properties in the mammalian collecting duct. Special emphasis is given to the mechanisms of how K(+) transport is regulated in the collecting duct.
Collapse
Affiliation(s)
- S Muto
- Department of Nephrology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
| |
Collapse
|
9
|
Erichsen S, Stierna P, Bagger-Sjöbäck D, Curtis LM, Rarey KE, Schmid W, Hultcrantz M. Distribution of Na,K-ATPase is normal in the inner ear of a mouse with a null mutation of the glucocorticoid receptor. Hear Res 1998; 124:146-54. [PMID: 9822912 DOI: 10.1016/s0378-5955(98)00117-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
This study was performed in order to test the hypothesis that the glucocorticoid hormone stimulates the formation of Na,K-ATPase in the inner ear of the mouse. An immunohistochemical study with respect to the presence and distribution of glucocorticoid receptors (GR) and Na,K-ATPase in the vestibular and cochlear regions of the inner ear was performed on a C57BL mouse with a null mutation of the glucocorticoid receptor (GR mutant mouse). The wild type C57BL mouse and the CBA mouse served as normal controls. As expected, the homozygous GR mutant mouse showed no specific staining for GR in the inner ear. The heterozygous GR mutant mouse showed faint staining of GR in the spiral limbus, the spiral ganglion, the organ of Corti and the utricle. This staining was markedly less than in the wild type C57BL mouse. Antibody labelling of Na,K-ATPase in the inner ear showed no significant difference between the homozygous and the heterozygous GR mutant mouse as compared to the control wild type C57BL mouse or the CBA mouse. Although earlier studies have shown a positive correlation between levels of glucocorticoid hormone in serum and the concentration of Na,K-ATPase in the inner ear, the hypothesis that glucocorticoid hormones alone stimulate the formation of Na,K-ATPase in the inner ear could not be confirmed by this study. Thus other regulating substances must be considered.
Collapse
Affiliation(s)
- S Erichsen
- Department of Otorhinolaryngology, Karolinska Hospital, Stockholm, Sweden
| | | | | | | | | | | | | |
Collapse
|
10
|
Wald H, Garty H, Palmer LG, Popovtzer MM. Differential regulation of ROMK expression in kidney cortex and medulla by aldosterone and potassium. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:F239-45. [PMID: 9691014 DOI: 10.1152/ajprenal.1998.275.2.f239] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
This study explores the role of K+ and aldosterone in the regulation of mRNA of the ATP-sensitive, inwardly rectifying K+ channel, ROMK, in the rat kidney. K+ deficiency downregulated ROMK mRNA in cortex to 47.1 +/- 5.1% of control (P < 0.001) and in medulla to 56.1 +/- 3. 4% (P < 0.001). High-K+ diet slightly increased ROMK mRNA in medulla to 122 +/- 9% (P < 0.05 vs. control). Adrenalectomy (Adx) downregulated cortical ROMK mRNA to 30.7 +/- 6.8% (P < 0.001 vs. control), and increased it in medulla to 138 +/- 12.9% (P < 0.02 vs. control). In Adx rats, K+ deficiency decreased ROMK mRNA in cortex and medulla similar to intact rats. The alpha1- and beta1-Na-K-ATPase subunits were regulated in parallel to that of ROMK. In medulla, ROMK mRNA correlated with serum K+ concentration at R = 0.9406 (n = 6, P < 0.001) and alpha1-Na-K-ATPase mRNA at R = 0.9756 (n = 6, P < 0.001). ROMK2 also correlated with serum K+ concentration (R = 0.895; n = 6, P < 0.01). These results show that cortical ROMK expression is regulated by aldosterone and K+, whereas the medullary ROMK mRNA is regulated by serum K+.
Collapse
Affiliation(s)
- H Wald
- Nephrology and Hypertension Services, Hadassah University Hospital, Jerusalem 91120, Israel
| | | | | | | |
Collapse
|
11
|
Lyoussi B, Crabbé J. Effects of corticosteroids on parameters related to Na+ transport by amphibian renal distal cells (A6) in culture. J Steroid Biochem Mol Biol 1996; 59:323-31. [PMID: 9010324 DOI: 10.1016/s0960-0760(96)00123-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The present study addresses the effects of the hormones aldosterone and corticosterone, as well as those of dexamethasone, on cultured renal amphibian cells, focusing on parameters thought relevant for the further understanding of the regulation by these steroids of Na+ reabsorption along the renal tubule. Exposure to these steroids of A6 cell monolayers grown on a permeable support produced a motor, dose-dependent, increase in Na+ transport, reflected by the short-circuit current, Isc. (Na+ + K+)-ATPase activity and ouabain binding, both of which are linearly correlated with Isc in control tissue, also increased significantly after steroid treatment. Dexamethasone was consistently more active than corticosterone and aldosterone on the parameters studied. The increase in Isc and (Na+ + K+)-ATPase activity elicited by dexamethasone could be blocked by the glucocorticoid antagonist RU 486, whereas it was only slightly reduced by the mineralocorticoid antagonist, spironolactone. In contrast, the latter strikingly reduced the effects of aldosterone on these parameters, unlike RU 486. Furthermore, the effects of large doses of dexamethasone and aldosterone combined were not additive. Taken together, the data presented appear compatible with the view that the effects of aldosterone on Na+ transport by A6 cells are mediated by a fraction of the receptors involved in the response to dexamethasone; they furthermore raise the question of whether, in lower vertebrates, it is relevant to make a distinction between "gluco" and "mineralo"corticoids.
Collapse
Affiliation(s)
- B Lyoussi
- Departement de Physiologie, Université Catholique de Louvain, Bruxelles, Belgium
| | | |
Collapse
|
12
|
Escoubet B, Coureau C, Blot-Chabaud M, Bonvalet JP, Farman N. Corticosteroid receptor mRNA expression is unaffected by corticosteroids in rat kidney, heart, and colon. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 270:C1343-53. [PMID: 8967434 DOI: 10.1152/ajpcell.1996.270.5.c1343] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Hormones can regulate the expression of their own receptor. We have examined whether adrenalectomy (ADX) and hormone replacement by physiological doses of aldosterone or dexamethasone could modulate the expression of glucocorticoid receptor (GR) or mineralocorticoid receptor (MR) at the mRNA level in the rat kidney, distal colon, and heart. Adult rats were adrenalectomized and received or did not receive an infusion of aldosterone (5 micrograms.100 g-1.day-1) or dexamethasone (10 micrograms.100 g-1.day-1). No significant change in steady-state levels of both MR and GR mRNA was detectable by using ribonuclease (RNase) protection assay (RPA) after either ADX or hormone replacement. Because the kidney is heterogeneous with regard to MR expression, RPA was adapted for measurements on microdissected nephron segments. GR mRNA is expressed at comparable levels all along the nephron, whereas MR mRNA is restricted to the distal nephron. No effect of ADX or GR and MR mRNA levels was detected in any nephron segment that was either aldosterone sensitive or insensitive. In situ hybridization confirmed the absence of corticosteroid-dependent modulation of MR mRNA in all kidney cell types. We conclude that variations of corticosteroid status do not affect MR and GR mRNA steady-state levels in heart, colon, and kidney and thus do not participate to the functional adaptations that are known to depend on hormonal status.
Collapse
Affiliation(s)
- B Escoubet
- Institut National de la Santé et de la Recherche Médicale U246, Faculté de Médecine Xavier Bichat, Paris, France
| | | | | | | | | |
Collapse
|
13
|
Ma YL, Gerhardt KJ, Curtis LM, Rybak LP, Whitworth C, Rarey KE. Combined effects of adrenalectomy and noise exposure on compound action potentials, endocochlear potentials and endolymphatic potassium concentrations. Hear Res 1995; 91:79-86. [PMID: 8647728 DOI: 10.1016/0378-5955(95)00172-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The effects of removal of endogenous corticosteroids via bilateral adrenalectomy in combination with noise exposure (30 min at 100 dB) were determined by recording compound action potential (CAP) and endocochlear potentials (EP), and by measuring potassium concentrations (K+e) within the endolymph. Thirty-eight Long-Evans rats were divided into groups according to experimental treatments: adrenalectomy (ADX) or non-ADX and noise exposure or non-noise exposure. CAP thresholds, EP and K+e values were subjected to repeated-measures analysis of variance with group and time as factors classifying the measurements. Noise exposure resulted in significant elevations of CAP thresholds in both the ADX and non-ADX animals, but had no effect on either EP or endolymphatic K+e. Recovery was noted during all post-exposure measurement periods and was significantly faster for ADX animals. EP and K+e did not change during or after noise exposure. ADX animals showed a non-significant reduction of EP and a statistically significant increase of K+e during all measurement periods as compared to non-ADX animals.
Collapse
Affiliation(s)
- Y L Ma
- Department of Anatomy and Cell Biology, University of Florida, Gainesville 32610, USA
| | | | | | | | | | | |
Collapse
|
14
|
EIAM-ONG S, TUNGSANGA K, TOSUKHOWONG P, SITPRIJA V. Renal ATPase-associated disorders. Nephrology (Carlton) 1995. [DOI: 10.1111/j.1440-1797.1995.tb00026.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
15
|
Coutry N, Farman N, Bonvalet JP, Blot-Chabaud M. Synergistic action of vasopressin and aldosterone on basolateral Na(+)-K(+)-ATPase in the cortical collecting duct. J Membr Biol 1995; 145:99-106. [PMID: 7636889 DOI: 10.1007/bf00233310] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The respective effects of aldosterone and arginine vasopressin (AVP) were examined on the number of active Na(+)-K(+)-ATPase and their pumping activity in nonperfused microdissected mouse cortical collecting tubules (CCD) by measuring specific 3H-ouabain binding and ouabain-sensitive 86Rb uptake. In adrenalectomized (ADX) animals, incubation of CCD with AVP (10(-8) M for 5 min) had no effect on the number of pumps. In contrast, in ADX animals replete with aldosterone, AVP induced a approximately equal to 40% increase in the number of pumps. This was accompanied by a approximately equal to 60-65% increase in ouabain-sensitive Rb uptake. AVP effect was dose-dependent (10(-10)-10(-8) M) and was reproduced by dDAVP, forskolin and 8-Br cAMP, indicating a V2 pathway. It was inhibited by amiloride 10(-5) M, and did not occur in CCD incubated in hyperosmotic solution, suggesting that the signal was transmitted via apical sodium entry and cell swelling. Finally, the AVP-dependent increase in the number of pumps was rapid (within 5 min) and transient (< 25 min). These results demonstrate that, in the CCD, aldosterone and AVP act synergistically to increase not only the apical sodium entry but also the basolateral Na(+)-K(+)-ATPase transport capacity: AVP allows a rapid recruitment and/or activation of an aldosterone-dependent pool of latent Na(+)-K(+)-ATPase.
Collapse
Affiliation(s)
- N Coutry
- INSERM U426, IFR "Cellules Epithéliales", Faculté X. Bichat, Paris, France
| | | | | | | |
Collapse
|
16
|
Aldosterone-mediated Na/K-ATPase expression is alpha 1 isoform specific in the renal cortical collecting duct. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)49486-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
|
17
|
Eiam-Ong S, Kurtzman NA, Sabatini S. Regulation of collecting tubule adenosine triphosphatases by aldosterone and potassium. J Clin Invest 1993; 91:2385-92. [PMID: 8390478 PMCID: PMC443296 DOI: 10.1172/jci116471] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
To examine the precise role of potassium and aldosterone on acid-base composition and on collecting tubule ATPases, glucocorticoid-replete adrenalectomized rats were replaced with zero, physiological, or pharmacological doses of aldosterone and were fed varying potassium diets to produce hypokalemia, normokalemia, or hyperkalemia. Radiochemical measurement of ATPase activities showed that collecting tubule H/K-ATPase changed inversely with potassium and not with aldosterone whereas H-ATPase changed directly with aldosterone but not with potassium. When both enzymes changed in the same direction, alterations in acid-base composition were profound; however, when these two acidifying enzymes changed in opposite directions or when only one enzyme changed, the effect on acid-base balance was modest. Serum bicarbonate was approximately 45 meq/liter when aldosterone was high and potassium was low; it was only 29 meq/liter when aldosterone was high but potassium was normal or when aldosterone was normal and potassium was low. Our observations may help explain the metabolic alkalosis of primary aldosteronism in which aldosterone excess and hypokalemia are combined and the metabolic acidosis of aldosterone deficiency in which hypoaldosteronism and hyperkalemia are paired. The present study also demonstrated that aldosterone plays the major role in controlling Na/K-ATPase activity in cortical collecting tubule. Hypokalemia stimulates Na/K-ATPase activity in the medullary collecting tubule; this stimulatory effect of hypokalemia supports the hypothesis that the enzyme is present on the apical membrane at this site.
Collapse
Affiliation(s)
- S Eiam-Ong
- Department of Internal Medicine, Texas Tech University Health Sciences Center, Lubbock 79430
| | | | | |
Collapse
|
18
|
Eiam-Ong S, Kurtzman NA, Sabatini S. Effect of furosemide-induced hypokalemic metabolic alkalosis on renal transport enzymes. Kidney Int 1993; 43:1015-20. [PMID: 8389946 DOI: 10.1038/ki.1993.143] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Hypokalemic metabolic alkalosis is one of the most common complications of chronic furosemide administration. In this study we examined acid-base composition and ATPase enzyme activities in medullary thick ascending limb of Henle's loop (MTAL) and collecting tubule (CCT and MCT) after seven days of chronic furosemide therapy. All of the studies were conducted in adrenal intact (AI) rats or in adrenalectomized (ADX) glucocorticoid replete rats replaced with a physiological dose of aldosterone (Aldo). Furosemide (F) was administered to each rat by mini-osmotic pump. In the AI+F group, plasma Aldo was high and obvious metabolic alkalosis occurred (HCO3- = 37 +/- 2 mEq/liter vs. 22 +/- 2 mEq/liter in controls, P < 0.005); activities of H-K-ATPase, H-ATPase, and Na-K-ATPase were increased approximately twofold in both CCT and MCT. In the ADX+F group (HCO3- = 28 +/- 2 mEq/liter, P < 0.05 from control), H-ATPase activity was normal in CCT and it was slightly increased in MCT. CCT and MCT H-K-ATPase activities were markedly increased (approximately twofold). Na-K-ATPase activity was the same as control in CCT but it was increased in MCT. In ADX+F+Vanadate (V) group which also had normal Aldo levels, acid-base changes were modest (20 +/- 2 mEq/liter, NS from control); in CCT and MCT H-K-ATPase and Na-K-ATPase activities were markedly reduced, but H-ATPase activity in MCT was increased. In all three experimental groups Na-K-ATPase activity in MTAL was reduced fivefold. Hypokalemia developed in both intact and ADX animals receiving furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- S Eiam-Ong
- Department of Internal Medicine, Texas Tech University Health Sciences Center, Lubbock
| | | | | |
Collapse
|
19
|
|
20
|
Ebata S, Muto S, Asano Y. Effects of uninephrectomy on electrical properties of the cortical collecting duct from rabbit remnant kidneys. J Clin Invest 1992; 90:1547-57. [PMID: 1328301 PMCID: PMC443202 DOI: 10.1172/jci116023] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Microelectrode techniques were used to determine the Na+ and K+ transport properties of the collecting duct cell in the isolated cortical collecting duct (CCD) from rabbits 14 d after uninephrectomy (UNX); results were compared with those from sham-operated rabbits (control). UNX had no effects on plasma aldosterone levels. The CCDs from UNX rabbits exhibited structural hypertrophy. The lumen negative transepithelial voltage and the basolateral membrane voltage (VB) were elevated in the UNX group. Although the transepithelial conductance (GT) and the fractional apical membrane resistance (fRA) were not different between the two groups, the conductances of the apical and the basolateral membranes were increased, and the tight junction conductance was decreased in the UNX group. The amiloride-sensitive changes in apical membrane voltage (VA), fRA, and GT were greater in the UNX group. The changes in VA upon raising the perfusate K+ concentration and the changes in VA and GT upon addition of Ba2+ to the perfusate were elevated in the UNX group. Upon raising K+ in the bath, a large depolarization of VB was observed in the UNX group. Lowering the bath Cl- resulted in a small depolarization of VB in the UNX group. Addition of Ba2+ to the bath in the UNX group caused the VB to hyperpolarize in parallel with decreases in GT and fRA whereas in the control group it had no effect on VB. Addition of ouabain to the bath resulted in a large depolarization of VB in the UNX group. We conclude that (a) UNX stimulates conductances of Na+ and K+ in the apical membrane, active Na(+)-K+ pump activity, and K+ conductance in the basolateral membrane, independently of plasma aldosterone; (b) The basolateral membrane in the tubules of UNX rabbits is more selective to K+; and (c) the hyperpolarization of VB upon UNX may increase passive K+ entry into the cell across the basolateral membrane.
Collapse
Affiliation(s)
- S Ebata
- Department of Nephrology, Jichi Medical School, Tochigi, Japan
| | | | | |
Collapse
|
21
|
|
22
|
Hays SR. Mineralocorticoid modulation of apical and basolateral membrane H+/OH-/HCO3- transport processes in the rabbit inner stripe of outer medullary collecting duct. J Clin Invest 1992; 90:180-7. [PMID: 1321841 PMCID: PMC443079 DOI: 10.1172/jci115834] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
To examine the mechanism by which mineralocorticoids regulate HCO3- absorption in the rabbit inner stripe of the outer medullary collecting duct, we microfluorometrically measured intracellular pH (pHi) in in vitro perfused tubules using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) assaying the apical and basolateral membrane H+/OH-/HCO3- transport processes in three groups of animals: those receiving chronic in vivo DOCA treatment (5 mg/kg per d x 2 wk); those with surgical adrenalectomy (ADX, [chronic x 2 wk]) on glucocorticoid replacement; and controls. Baseline pHi was not different in the three groups. Cellular volume (vol/mm) was increased 38% in DOCA tubules versus controls, but unchanged in ADX tubules versus controls. Buffer capacities (BT) were not different in the three groups. Apical membrane H+ pump activity, assayed as the Na(+)-independent pHi recovery from an acid load (NH3/NH4+ prepulse) and expressed as JH (dpHi/dt.vol/mm.BT) was increased 76% in DOCA tubules versus controls, and decreased 56% in ADX tubules versus controls. Basolateral membrane Cl-/HCO3- exchange activity assayed as the pHi response to basolateral Cl- addition was increased 73% in DOCA tubules versus controls, and decreased 44% in ADX tubules versus controls. When examined as a function of varying [Cl-], the Vmax of Cl-/HCO3- exchange activity was significantly increased in DOCA tubules (control, 72.7 +/- 15.7 pmol.mm-1.min-1 vs DOCA, 132.3 +/- 22.5 pmol.mm-1.min-1, P less than 0.02), while the K1/2 for Cl- was unchanged. Basolateral membrane Na+/H+ antiporter activity assayed as the Na(+)-dependent pHi recovery from an acid load was not changed in chronic DOCA tubules versus controls. In conclusion, the apical membrane H+ pump and basolateral membrane Cl-/HCO3- exchanger of the rabbit OMCDi are regulated in parallel without chronic alterations in pHi under the conditions of mineralocorticoid excess and deficiency. The parallel changes in these transporters accounts for the alterations in OMCDi HCO3- absorption seen under these conditions.
Collapse
Affiliation(s)
- S R Hays
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235
| |
Collapse
|
23
|
Abstract
Mineralocorticoid hormones are a subset of steroid hormones that act primarily in epithelial tissues to regulate ion transport of Na+, K+ and H+. Cellular specificity is conferred by receptors which act in the nucleus to stimulate gene expression. Transcription and subsequent translation result in the production of new proteins which mediate the physiologic effects. The mechanisms involved in receptor specificity and localization, in regulation of gene activation, and in expression of transport effects are reviewed. The cellular actions of mineralocorticoids fit well with the general model of steroid hormone action but considerable questions remain at each step in the process.
Collapse
Affiliation(s)
- J P Johnson
- Department of Nephrology, Walter Reed Army Institute of Research, Washington D.C. 20307
| |
Collapse
|
24
|
Salem MM, Rosa RM, Batlle DC. Extrarenal potassium tolerance in chronic renal failure: implications for the treatment of acute hyperkalemia. Am J Kidney Dis 1991; 18:421-40. [PMID: 1928061 DOI: 10.1016/s0272-6386(12)80110-7] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The role of extrarenal potassium homeostasis is well recognized as a major mechanism for the acute defense against the development of hyperkalemia. The purpose of this report is to examine whether or not the various mechanisms of extrarenal potassium regulation are intact in patients with end-stage renal disease (ESRD). The available data suggest that with the development of ESRD and the uremic syndrome there is impaired extrarenal potassium metabolism that is related to a defect in the Na,K-adenosine triphosphatase (ATPase). The responsiveness of uremic patients to the various effector systems that regulate extrarenal potassium handling is discussed. Insulin is well positioned to play an important role in the regulation of plasma potassium concentration in patients with impaired renal function. The role of basal insulin may be even more important than previously appreciated, since somatostatin infusion causes a much greater increase in the fasting plasma potassium in rats with renal failure than in controls. Furthermore, stimulation of endogenous insulin by oral glucose results in a greater intracellular translocation of potassium in uremic rats than in controls. Under at least two common physiologic circumstances, feeding and vigorous exercise, endogenous catecholamines might also act to defend against acute increments in extracellular potassium concentration. However, it is important to appreciate that the response to beta 2-adrenoreceptor-mediated internal potassium disposal is heterogeneous as judged by the variable responses to epinephrine infusion. Based on the evidence presented in this report, a regimen for the treatment of life-threatening hyperkalemia is outlined. Interpretation of the available data demonstrate that bicarbonate should not be relied on as the sole initial treatment for severe hyperkalemia, since the magnitude of the effect of bicarbonate on potassium is variable and may be delayed. The initial treatment for life-threatening hyperkalemia should always include insulin plus glucose, as the hypokalemic response to insulin is both prompt and predictable. Combined treatment with beta 2-agonists and insulin is also effective and may help prevent insulin-induced hypoglycemia.
Collapse
Affiliation(s)
- M M Salem
- Department of Medicine, Northwestern University Medical School, Chicago, IL
| | | | | |
Collapse
|
25
|
Abstract
The studies outlined in this review suggest that the immaturity of distal nephron segments may hinder urinary excretion of potassium early in life. Among the factors that may limit potassium secretion by principal cells in the neonatal cortical collecting duct are an unfavorable electrochemical gradient (reduced Ki, Na(+)-K(+)-ATPase activity and/or Vte), limited membrane permeability to potassium and sodium, low tubular fluid flow rate, reduced luminal sodium concentration, or increased paracellular backleak. Alternatively, enhanced potassium absorption by other relatively well-differentiated distal nephron segments may contribute in part to a reduced net potassium excretory rate in the newborn. It should be kept in mind, however, that the limited potassium secretory capacity of the immature kidney becomes clinically relevant only under conditions of potassium excess. Under normal circumstances, the tendency of the newborn to retain potassium is an appropriate and necessary condition for growth.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- L M Satlin
- Department of Pediatrics, Albert Einstein College of Medicine, Bronx, NY 10461
| |
Collapse
|
26
|
Lingrel JB, Orlowski J, Shull MM, Price EM. Molecular genetics of Na,K-ATPase. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1990; 38:37-89. [PMID: 2158121 DOI: 10.1016/s0079-6603(08)60708-4] [Citation(s) in RCA: 302] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Researchers in the past few years have successfully used molecular-genetic approaches to determine the primary structures of several P-type ATPases. The amino-acid sequences of distinct members of this class of ion-transport ATPases (Na,K-, H,K-, and Ca-ATPases) have been deduced by cDNA cloning and sequencing. The Na,K-ATPase belongs to a multiple gene family, the principal diversity apparently resulting from distinct catalytic alpha isoforms. Computer analyses of the hydrophobicity and potential secondary structure of the alpha subunits and primary sequence comparisons with homologs from various species as well as other P-type ATPases have identified common structural features. This has provided the molecular foundation for the design of models and hypotheses aimed at understanding the relationship between structure and function. Development of a hypothetical transmembrane organization for the alpha subunit and application of site-specific mutagenesis techniques have allowed significant progress to be made toward identifying amino acids involved in cardiac glycoside resistance and possibly binding. However, the complex structural and functional features of this protein indicate that extensive research is necessary before a clear understanding of the molecular basis of active cation transport is achieved. This is complicated further by the paucity of information regarding the structural and functional contributions of the beta subunit. Until such information is obtained, the proposed model and functional hypotheses should be considered judiciously. Considerable progress also has been made in characterizing the regulatory complexity involved in expression of multiple alpha-isoform and beta-subunit genes in various tissues and cells during development and in response to hormones and cations. The regulatory mechanisms appear to function at several molecular levels, involving transcriptional, posttranscriptional, translational, and posttranslational processes in a tissue- or cell-specific manner. However, much research is needed to precisely define the contributions of each of these mechanisms. Recent isolation of the genes for these subunits provides the framework for future advances in this area. Continued application of biochemical, biophysical, and molecular genetic techniques is required to provide a detailed understanding of the mechanisms involved in cation transport of this biologically and pharmacologically important enzyme.
Collapse
Affiliation(s)
- J B Lingrel
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Ohio 45267
| | | | | | | |
Collapse
|
27
|
Wang WH, Henderson RM, Geibel J, White S, Giebisch G. Mechanism of aldosterone-induced increase of K+ conductance in early distal renal tubule cells of the frog. J Membr Biol 1989; 111:277-89. [PMID: 2557452 DOI: 10.1007/bf01871012] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Isolated early distal tubule cells (EDC) of frog kidney were incubated for 20-28 hr in the presence of aldosterone and then whole-cell K+ currents were measured at constant intracellular pH by the whole-cell voltage-clamp technique. Aldosterone increased barium-inhibitable whole-cell K+ conductance (gK+) threefold. This effect was reduced by amiloride and totally abolished by ouabain. However, aldosterone could still raise gK- in ouabain-treated cells in the presence of furosemide. We tested whether changes in intracellular pH (pHi) could be a signal for cells to regulate gK+. After removal of aldosterone, the increase in gK+ was preserved by subsequent incubation for 8 hr at pH 7.6 but abolished at pH 6.6. In the complete absence of aldosterone, incubation of cells at pH 8.0 for 20-28 hr raised pHi and doubled gK+. Using the patch-clamp technique, three types of K+-selective channels were identified, which had conductances of 24, 45 and 59 pS. Aldosterone had no effect on the conductance or open probability (Po) of any of the three types of channels. However, the incidence of observing type II channels was increased from 4 to 22%. Type II channels were also found to be pH sensitive, Po was increased by raising pH. These results indicate that prolonged aldosterone treatment raises pHi and increases gK+ by promoting insertion of K+ channels into the cell membrane. Channel insertion is itself triggered by raising both pHi and increasing the activity of the Na+/K+ pump in early distal cells of frog kidney.
Collapse
Affiliation(s)
- W H Wang
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
| | | | | | | | | |
Collapse
|
28
|
Grillo C, Coirini H, McEwen BS, De Nicola AF. Changes of salt intake and of (Na+K)-ATPase activity in brain after high dose treatment with deoxycorticosterone. Brain Res 1989; 499:225-33. [PMID: 2553208 DOI: 10.1016/0006-8993(89)90770-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Mineralocorticoids (MC) have a dual effect on salt intake: in adrenalectomized rats, they reduce previously elevated salt intake; and in intact rats a high MC dose increases salt intake. We have studied the activity of (Na+K)-ATPase and [3H]ouabain binding in rats treated with deoxycorticosterone (DOC) in doses that elicited a salt appetite. Brains were removed from control and treated animals, and 20 different areas were punched out from brain slices cut every 300 microns. DOC treatment significantly reduced (Na+K)-ATPase activity in the lateral hypothalamic area, anterior amygdaloid and lateral amygdaloid nuclei, while increasing it in the periventricular gray matter; changes in other regions were not significant. Binding of [3H]ouabain was not modified by DOC treatment. In parallel experiments, we determined MC receptors in adrenalectomized rats. Binding of [3H]aldosterone was preferentially found in hippocampus, followed by lateral septum, anterior, posterior and lateral amygdaloid areas, with lower levels in other regions. However, there was no correlation between [3H]aldosterone binding and (Na+K)-ATPase activity in brain punches from either control or DOC-treated rats. Further experiments are needed to ascertain if (Na+K)-ATPase changes in discrete areas of the brain containing moderate levels of mineralocorticoid receptors, are related to the behavioral effects of DOC.
Collapse
Affiliation(s)
- C Grillo
- Laboratorio de Bioquímica Neuroendócrina, Instituto de Biología y Medicina Experimental, Buenos Aires, Argentina
| | | | | | | |
Collapse
|
29
|
Doucet A. Function and control of Na-K-ATPase in single nephron segments of the mammalian kidney. Kidney Int 1988; 34:749-60. [PMID: 2850394 DOI: 10.1038/ki.1988.245] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
|
30
|
Grossman EB, Hebert SC. Modulation of Na-K-ATPase activity in the mouse medullary thick ascending limb of Henle. Effects of mineralocorticoids and sodium. J Clin Invest 1988; 81:885-92. [PMID: 2830316 PMCID: PMC442541 DOI: 10.1172/jci113399] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
This study investigates the effect of variations in mineralocorticoid as well as cell sodium delivery and uptake on Na-K-ATPase activity in the mouse medullary thick ascending limb of Henle (mTALH). Pharmacologic doses of the mineralocorticoid deoxycorticosterone acetate (DOCA) resulted in a 28% increase of Na-K-ATPase activity. Furosemide-induced inhibition of sodium uptake by the mTALH cell also resulted in Na-K-ATPase activity reduction (45%). Sodium deprivation did not cause a clear change in enzyme activity, either at 3 d or 2 wk, likely reflecting the result of the opposing influences of decreased sodium delivery and increased endogenous aldosterone. Finally, the behavior of Na-K-ATPase activity at 3 d of sodium deprivation in the mTALH contrasted with a 60% increase in activity observed in the cortical collecting tubule, a nephron segment known to be responsive to mineralocorticoid, and this heterogeneity of response may suggest an important role for the mTALH in maintaining salt homeostasis.
Collapse
Affiliation(s)
- E B Grossman
- Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | | |
Collapse
|
31
|
Muto S, Sansom S, Giebisch G. Effects of a high potassium diet on electrical properties of cortical collecting ducts from adrenalectomized rabbits. J Clin Invest 1988; 81:376-80. [PMID: 3339125 PMCID: PMC329579 DOI: 10.1172/jci113329] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The cortical collecting tubule is one of the main nephron sites where mineralocorticoids and a high potassium diet modulate sodium (Na) and potassium (K) transport. In this study we explored the steroid-independent effects of a high K diet on the electrical transport properties of the isolated rabbit cortical collecting tubule principal cells. The electrophysiological analysis included transepithelial and single-cell potential measurements and equivalent circuit analysis. Rabbits were adrenalectomized (ADX) and received either a control diet (300 meq K/kg diet) or a high K diet (600 meq/kg diet) for 10 d before the experiment. The mean plasma K of ADX control animals was 6.9 mM, that of ADX animals on the high K diet 8.3 mM. The transepithelial potential difference was significantly elevated in the high K group (-3.5 mV, lumen negative), compared with ADX controls (-1.4 mV). The basolateral membrane potential in high K animals was also significantly elevated (-73 mV, cell negative, compared with -63 mV in controls). Estimates of the apical membrane partial Na and K conductances (GaNa and GaK) and of ion currents (IaNa and IaK) also demonstrated stimulation by the high K diet. In the high K group, both GaNa and GaK (0.56 and 2.67 mS.cm-2) were higher than control values (0.27 and 1.17 mS.cm-2). IaNa and IaK were also higher in high K animals (47.8 and -26.2 microA.cm-2) compared with control animals (22.4 and -11.6 microA.cm-2). Thus, a high K intake per se can induce electrophysiological changes consistent with stimulation of Na reabsorption and K secretion.
Collapse
Affiliation(s)
- S Muto
- Department of Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
| | | | | |
Collapse
|
32
|
Abstract
The possibility that endogenous inhibitors of the sodium pump exist and bind to the cardiac glycoside binding site on Na+,K+-adenosine triphosphatase (ATPase) has been a source of much controversy. Although numerous hormones and inorganic ions that modulate Na+,K+-ATPase activity have been described, most of these affect the sodium pump indirectly by varying the intracellular sodium concentration or by increasing the number of enzyme units. None of these endogenous compounds has been shown conclusively to modulate sodium pump activity by binding to the cardiac glycoside binding site on Na+,K+-ATPase. However, the near-universal presence of three high-affinity binding sites on the alpha-subunit of the enzyme has engendered much speculation that endogenous ligands for these receptors must exist. In addition, none of the hormones known to indirectly affect sodium pump activity in vivo has been shown to modulate Na+,K+-ATPase activity in response to extracellular volume expansion or to play a role in the pathogenesis of hypertension or chronic renal failure, conditions in which a circulating inhibitor of Na+,K+-ATPase has been implicated. This report presents a condensed history of the search for endogenous inhibitors of Na+,K+-ATPase and describes recent advances in the field. Despite progress in identifying and characterizing compounds that could affect Na+,K+-ATPase activity in vivo, definitive proof for the existence of endogenous ligands for the cardiac glycoside binding site remains elusive.
Collapse
Affiliation(s)
- R A Kelly
- Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115
| |
Collapse
|
33
|
Oberleithner H, Weigt M, Westphale HJ, Wang W. Aldosterone activates Na+/H+ exchange and raises cytoplasmic pH in target cells of the amphibian kidney. Proc Natl Acad Sci U S A 1987; 84:1464-8. [PMID: 3029782 PMCID: PMC304451 DOI: 10.1073/pnas.84.5.1464] [Citation(s) in RCA: 131] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The hypothesis was tested if the mineralocorticoid hormone aldosterone stimulates Na+/H+ exchange in "giant cells" fused from individual target cells of the distal nephron of the frog kidney. By means of microelectrodes, steady-state intracellular pH (pHi) and pHi recovery from an acid load were recorded continuously while the fused cells were exposed to aldosterone. Twenty minutes after addition of the hormone, pHi started to rise and reached a new steady state after about 60 min (delta pHi = 0.28 +/- 0.01). After hormone treatment, pHi recovered significantly faster in response to an intracellular acid load. The diuretic drug amiloride blocked pHi recovery. Experiments in intact tubules showed that aldosterone induces H+ and K+ secretion. Thus, intracellular alkalosis, mediated by Na+/H+ exchange, could serve as a signal that activates pH-sensitive K+ channels of the luminal cell membrane.
Collapse
|
34
|
|
35
|
Chapter 11 Renal Potassium Adaptation: Cellular Mechanisms and Morphology. ACTA ACUST UNITED AC 1987. [DOI: 10.1016/s0070-2161(08)60415-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
|
36
|
Stanton B, Pan L, Deetjen H, Guckian V, Giebisch G. Independent effects of aldosterone and potassium on induction of potassium adaptation in rat kidney. J Clin Invest 1987; 79:198-206. [PMID: 3793923 PMCID: PMC424022 DOI: 10.1172/jci112783] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We examined the independent effects of a high potassium diet and increased aldosterone levels on the development of renal potassium adaptation. This condition is defined by the increased ability of the kidneys to excrete an acute infusion of potassium. Rats were adrenalectomized (ADX) and received aldosterone at basal levels (0.5 microgram/100 g X d) or at high levels (2.0 micrograms/100 g X d) for 10 d. In each experimental group, animals received either a control diet or a high potassium diet. In ADX animals with basal aldosterone levels, a high potassium intake increased but did not completely restore the ability to excrete potassium and induced proliferation of the basolateral membrane of principal cells in the collecting tubule (i.e., morphologic adaptation). In contrast, increased aldosterone did not induce functional adaptation. Elevated aldosterone and dietary potassium intake were required to produce functional potassium adaptation indistinguishable from that in potassium-loaded, adrenal-intact animals.
Collapse
|
37
|
O'neil RG. Chapter 9 Adrenal Steroid Regulation of Potassium Transport. CURRENT TOPICS IN MEMBRANES AND TRANSPORT 1987. [DOI: 10.1016/s0070-2161(08)60413-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
|
38
|
Stanton BA. Regulation by adrenal corticosteroids of sodium and potassium transport in loop of Henle and distal tubule of rat kidney. J Clin Invest 1986; 78:1612-20. [PMID: 3023448 PMCID: PMC423933 DOI: 10.1172/jci112754] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Studies were conducted to examine the effects of adrenalectomy (ADX) and selective, physiological adrenal corticosteroid replacement on sodium and potassium transport by the superficial loop of Henle and distal tubule of rat kidney in vivo. In the loop of Henle, ADX inhibited sodium reabsorption by 33%. Whereas dexamethasone had no effect on reabsorption, aldosterone increased sodium transport to control levels. Thus, physiological levels of mineralocorticoids, but not glucocorticoids, control a fraction of sodium reabsorption in the loop of Henle. ADX also inhibited potassium reabsorption in the loop of Henle. Both dexamethasone and aldosterone reversed the inhibition, although only aldosterone increased reabsorption to control levels. In the distal tubule, ADX reduced sodium reabsorption by 44%. Both aldosterone and dexamethasone stimulated reabsorption: however, only aldosterone increased transport to control. Potassium secretion by the distal tubule was also reduced 34% by ADX. Aldosterone, but not dexamethasone, stimulated secretion. Thus, physiological levels of aldosterone regulate a fraction of sodium reabsorption and potassium secretion in the distal tubule.
Collapse
|
39
|
Mujais SK. Regulation of renal Na-K-ATPase: effects of aldosterone in phosphate depletion. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1986; 208:485-92. [PMID: 3031949 DOI: 10.1007/978-1-4684-5206-8_60] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
|
40
|
Mujais SK, Kauffman S, Katz AI. Angiotensin II binding sites in individual segments of the rat nephron. J Clin Invest 1986; 77:315-8. [PMID: 3003153 PMCID: PMC423342 DOI: 10.1172/jci112293] [Citation(s) in RCA: 98] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The sites of action of angiotensin II along the nephron are not well defined and both proximal and distal effects are suggested. Using a microassay that permits measurement of hormone binding in discrete tubule segments, we determined the binding sites of 125I-angiotensin II along the nephron of Sprague-Dawley rats. Specific binding in proximal convoluted tubule (PCT) (at 25 degrees C, pH 7.4) was linearly related to tubule length and saturable, with an apparent maximal binding capacity of approximately 300 amol X cm-1. Binding specificity was verified in competition experiments that revealed significant (P less than 0.001) and comparable competition for radioligand binding by angiotensin II and angiotensin precursor, metabolite, and analogues, whereas unrelated peptides of similar size (bradykinin, ACTH [1-10]) were without effect. The profile of specific angiotensin II binding along the nephron was: PCT, 216 +/- 13; pars recta, 86 +/- 14; medullary thick ascending limb of Henle's loop, 46 +/- 8; cortical thick ascending limb of Henle's loop, 77 +/- 8; distal convoluted tubule, 49 +/- 10; cortical collecting tubule, 15 +/- 1; medullary collecting tubule, 32 +/- 7 amol X cm-1. These results indicate the presence of specific angiotensin II binding sites in all tubule segments studied, but binding capacity was highest in the proximal convoluted tubule, in agreement with transport studies that localize the effects of the hormone in this segment.
Collapse
|
41
|
|