1
|
Pelzl L, Pakladok T, Pathare G, Fakhri H, Michael D, Wagner CA, Paulmichl M, Lang F. DOCA sensitive pendrin expression in kidney, heart, lung and thyroid tissues. Cell Physiol Biochem 2012; 30:1491-501. [PMID: 23235354 DOI: 10.1159/000343337] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/23/2012] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND/AIMS Pendrin (SLC26A4), a transporter accomplishing anion exchange, is expressed in inner ear, thyroid gland, kidneys, lung, liver and heart. Loss or reduction of function mutations of SLC26A4 underlie Pendred syndrome, a disorder invariably leading to hearing loss with enlarged vestibular aqueducts and in some patients to hypothyroidism and goiter. Renal pendrin expression is up-regulated by mineralocorticoids such as aldosterone or deoxycorticosterone (DOCA). Little is known about the impact of mineralocorticoids on pendrin expression in extrarenal tissues. METHODS The present study utilized RT-qPCR and Western blotting to quantify the transcript levels and protein abundance of Slc26a4 in murine kidney, thyroid, heart and lung prior to and following subcutaneous administration of 100 mg/kg DOCA. RESULTS Slc26a4 transcript levels as compared to Gapdh transcript levels were significantly increased by DOCA treatment in kidney, heart, lung and thyroid. Accordingly pendrin protein expression was again significantly increased by DOCA treatment in kidney, heart, lung and thyroid. CONCLUSION The observations reveal mineralocorticoid sensitivity of pendrin expression in kidney, heart, thyroid and lung.
Collapse
Affiliation(s)
- Lisann Pelzl
- Department of Physiology, University of Tuebingen, Tuebingen, Germany
| | | | | | | | | | | | | | | |
Collapse
|
2
|
|
3
|
Oberleithner H, Kersting U, Gassner B. Aldosterone-controlled linkage between Na+/H+ exchange and K+ channels in fused renal epithelial cells. CIBA FOUNDATION SYMPOSIUM 2007; 139:201-19. [PMID: 2849527 DOI: 10.1002/9780470513699.ch12] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Aldosterone maintains acid-base balance and K+ homeostasis by controlling H+ and K+ secretion in renal epithelial cells. We have shown recently in the amphibian distal nephron that aldosterone activates a Na+/H+ exchange system in the luminal cell membrane, leading to transepithelial H+ secretion and cytoplasmic alkalinization. Since H+ secretory fluxes are paralleled by K+ secretion, it was postulated that the hormone-induced increase of intracellular pH activates the luminally located K+ channels. In 'giant' cells fused from individual cells of the distal nephron, we measured simultaneously cytoplasmic pH and cell membrane K+ conductance during acidification of the cell cytoplasm. The experiments demonstrate that cell membrane K+ conductance is half-maximal at an intracellular pH of 7.42, and that a positive cooperative interaction exists between K+ channel proteins and H+ ions (Hill coefficient = 6.5). Moreover, the cellular K+ conductance is most sensitive to cytoplasmic pH in the range modified by aldosterone. This supports the hypothesis that intracellular H+ activity, regulated by the Na+/H+ exchanger, serves as the signal to couple aldosterone-induced K+ secretory flux to H+ secretion in renal tubules.
Collapse
Affiliation(s)
- H Oberleithner
- Department of Physiology, University of Würzburg, Federal Republic of Germany
| | | | | |
Collapse
|
4
|
Affiliation(s)
- David W Good
- Department of Medicine, University of Texas Medical Branch, Galveston 77555-0562, USA.
| |
Collapse
|
5
|
Féraille E, Doucet A. Sodium-potassium-adenosinetriphosphatase-dependent sodium transport in the kidney: hormonal control. Physiol Rev 2001; 81:345-418. [PMID: 11152761 DOI: 10.1152/physrev.2001.81.1.345] [Citation(s) in RCA: 340] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Tubular reabsorption of filtered sodium is quantitatively the main contribution of kidneys to salt and water homeostasis. The transcellular reabsorption of sodium proceeds by a two-step mechanism: Na(+)-K(+)-ATPase-energized basolateral active extrusion of sodium permits passive apical entry through various sodium transport systems. In the past 15 years, most of the renal sodium transport systems (Na(+)-K(+)-ATPase, channels, cotransporters, and exchangers) have been characterized at a molecular level. Coupled to the methods developed during the 1965-1985 decades to circumvent kidney heterogeneity and analyze sodium transport at the level of single nephron segments, cloning of the transporters allowed us to move our understanding of hormone regulation of sodium transport from a cellular to a molecular level. The main purpose of this review is to analyze how molecular events at the transporter level account for the physiological changes in tubular handling of sodium promoted by hormones. In recent years, it also became obvious that intracellular signaling pathways interacted with each other, leading to synergisms or antagonisms. A second aim of this review is therefore to analyze the integrated network of signaling pathways underlying hormone action. Given the central role of Na(+)-K(+)-ATPase in sodium reabsorption, the first part of this review focuses on its structural and functional properties, with a special mention of the specificity of Na(+)-K(+)-ATPase expressed in renal tubule. In a second part, the general mechanisms of hormone signaling are briefly introduced before a more detailed discussion of the nephron segment-specific expression of hormone receptors and signaling pathways. The three following parts integrate the molecular and physiological aspects of the hormonal regulation of sodium transport processes in three nephron segments: the proximal tubule, the thick ascending limb of Henle's loop, and the collecting duct.
Collapse
Affiliation(s)
- E Féraille
- Division of Nephrology, Geneva University Hospital, Geneva, Switzerland.
| | | |
Collapse
|
6
|
Abstract
Eukaryotic chromosomes are confined to the nucleus, which is separated from the rest of the cell by two concentric membranes known as the nuclear envelope (NE). The NE is punctuated by holes known as nuclear pore complexes (NPCs), which provide the main pathway for transport of cellular material across the nuclear-cytoplasmic boundary. The single NPC is a complicated octameric structure containing more than 100 proteins called nucleoporins. NPCs function as transport machineries for inorganic ions and macromolecules. The most prominent feature of an individual NPC is a large central channel, ~7 nm in width and 50 nm in length. NPCs exhibit high morphological and functional plasticity, adjusting shape to function. Macromolecules ranging from 1 to >100 kDa travel through the central channel into (and out of) the nucleoplasm. Inorganic ions have additional pathways for communication between cytosol and nucleus. NE can turn from a simple sieve that separates two compartments by a given pore size to a smart barrier that adjusts its permeabiltiy to the metabolic demands of the cell. Early microelectrode work characterizes the NE as a membrane barrier of highly variable permeability, indicating that NPCs are under regulatory control. Electrical voltage across the NE is explained as the result of electrical charge separation due to selective barrier permeability and unequal distribution of charged macromolecules across the NE. Patch-clamp work discovers NE ion channel activity associated with NPC function. From comparison of early microelectrode work with patch-clamp data and late results obtained by the nuclear hourglass technique, it is concluded that NPCs are well-controlled supramolecular structures that mediate transport of macromolecules and small ions by separate physical pathways, the large central channel and the small peripheral channels, respectively. Electrical properties of the two pathways are still unclear but could have great impact on the understanding of signal transfer across NE and gene expression.
Collapse
Affiliation(s)
- M Mazzanti
- Dipartmento di Biologia Cellulare e dello Sviluppo, Università "la Sapienza," Rome, Italy
| | | | | |
Collapse
|
7
|
Young DB, McCabe RD. Endocrine Control of Potassium Balance. Compr Physiol 2000. [DOI: 10.1002/cphy.cp070308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
8
|
Maguire D, MacNamara B, Cuffe JE, Winter D, Doolan CM, Urbach V, O'Sullivan GC, Harvey BJ. Rapid responses to aldosterone in human distal colon. Steroids 1999; 64:51-63. [PMID: 10323673 DOI: 10.1016/s0039-128x(98)00096-8] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Aldosterone at normal physiological levels induces rapid increases in intracellular calcium and pH in human distal colon. The end target of these rapid signaling responses are basolateral K+ channels. Using spectrofluorescence microscopy and Ussing chamber techniques, we have shown that aldosterone activates basolateral Na/H exchange via a protein kinase C and calcium-dependent signaling pathway. The resultant intracellular alkalinization up-regulates an adenosine triphosphate (ATP)-dependent K+ channel (K(ATP)) and inhibits a Ca2+ -dependent K+ channel (K(Ca)). In Ussing chamber experiments, we have shown that the K(ATP) channel is required to drive sodium absorption, whereas the K(Ca) channel is necessary for both cyclic adenosine monophosphate and calcium-dependent chloride secretion. The rapid effects of aldosterone on intracellular calcium, pH, protein kinase C and K(ATP), K(Ca) channels are insensitive to cycloheximide, actinomycin D, and spironalactone, indicating a nongenomic mechanism of action. We propose that the physiological role for the rapid nongenomic effect of aldosterone is to prime pluripotential epithelia for absorption by simultaneously up-regulating K(ATP) channels to drive absorption through surface cells and down-regulating the secretory capacity by inhibiting K(Ca) channels involved in secretion through crypt cells.
Collapse
Affiliation(s)
- D Maguire
- Department of Physiology, National University of Ireland, Cork
| | | | | | | | | | | | | | | |
Collapse
|
9
|
Capasso G, Unwin R, Ciani F, De Santo NG, De Tommaso G, Russo F, Giebisch G. Bicarbonate transport along the loop of Henle. II. Effects of acid-base, dietary, and neurohumoral determinants. J Clin Invest 1994; 94:830-8. [PMID: 8040339 PMCID: PMC296164 DOI: 10.1172/jci117403] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The loop of Henle contributes to renal acidification by reabsorbing about 15% of filtered bicarbonate. To study the effects on loop of Henle bicarbonate transport (JHCO3) of acid-base disturbances and of several factors known to modulate sodium transport, these in vivo microperfusion studies were carried out in rats during: (a) acute and chronic metabolic acidosis, (b) acute and chronic (hypokalemic) metabolic alkalosis, (c) a control sodium diet, (d) a high-sodium diet, (e) angiotensin II (AII) intravenous infusion, (f) simultaneously intravenous infusion of both AII and the AT1 receptor antagonist DuP 753, (g) acute ipsilateral mechanicochemical renal denervation. Acute and chronic metabolic acidosis increased JHCO3; acute metabolic alkalosis significantly reduced JHCO3, whereas chronic hypokalemic alkalosis did not alter JHCO3. Bicarbonate transport increased in animals on a high-sodium intake and following AII administration, and the latter was inhibited by the AII (AT1) receptor antagonist DuP 753; acute renal denervation lowered bicarbonate transport. These data indicate that bicarbonate reabsorption along the loop of Henle in vivo is closely linked to systemic acid-base status and to several factors known to modulate sodium transport.
Collapse
Affiliation(s)
- G Capasso
- Faculty of Medicine, 1st. University of Naples, Italy
| | | | | | | | | | | | | |
Collapse
|
10
|
Vilella S, Guerra L, Helmle-Kolb C, Murer H. Aldosterone actions on basolateral Na+/H+ exchange in Madin-Darby canine kidney cells. Pflugers Arch 1992; 422:9-15. [PMID: 1331980 DOI: 10.1007/bf00381507] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In recent studies, there has been a re-evaluation of the polarity of Na+/H+ exchange in Madin-Darby canine kidney (MDCK) cells. This study was designed to examine aldosterone actions on basolaterally located Na+/H+ exchange of MDCK cell monolayers grown on permeant filter supports; pHi was analysed in the absence of bicarbonate by using the pH-sensitive fluorescent probe 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. Pre-exposure of MDCK cells to aldosterone led within 10-20 min to an alkalization of pHi (approximately 0.3 pH unit); this effect is prevented by an addition of dimethylamiloride to the basolateral superfusate. Addition of aldosterone led to stimulation of the basolaterally located Na+/H+ exchange activity (Na(+)-dependent recovery from an acid load); this effect required preincubation (more then 3 min) and was observed at 0.1 nM aldosterone. Pre-exposure (15 min) of MDCK monolayers to phorbol 12-myristate 13-acetate also led to an activation of Na+/H+ exchange; pre-exposure to 8-bromo-cAMP led to inhibition of Na+/H+ exchange activity. An inhibitory effect of aldosterone was observed if Na+/H+ exchange activity was analysed in the presence of aldosterone; the highest inhibitory effects (20%-30%) occurred at concentrations of 5 nM and higher. Aldosterone-dependent inhibition does not require preincubation and is fully reversible; it was only observed at low (20 mM) but not at high Na+ concentrations (130 mM). The data suggest that aldosterone has an instantaneous inhibitory effect on basolaterally located Na+/H+ exchange activity under conditions of low Na+, but stimulates the rate of transport activity upon preincubation under conditions of physiological Na+ concentrations.
Collapse
Affiliation(s)
- S Vilella
- Department of Physiology, University of Zürich, Switzerland
| | | | | | | |
Collapse
|
11
|
Coutry N, Blot-Chabaud M, Mateo P, Bonvalet JP, Farman N. Time course of sodium-induced Na(+)-K(+)-ATPase recruitment in rabbit cortical collecting tubule. THE AMERICAN JOURNAL OF PHYSIOLOGY 1992; 263:C61-8. [PMID: 1322044 DOI: 10.1152/ajpcell.1992.263.1.c61] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In cortical collecting tubules (CCD) of aldosterone-repleted rabbit kidney, an increase in intracellular sodium concentration (Nai) induces the recruitment and/or activation of latent Na(+)-K(+)-ATPase pumps (Blot-Chabaud et al., J. Biol. Chem. 265: 11676-11681, 1990). The present study was addressed to determine the time course of this Nai-dependent pump recruitment and to examine some of the factors possibly involved in this phenomenon. CCD from adrenalectomized rabbits complemented with aldosterone and dexamethasone were incubated at 4 degrees C either in a K(+)-free saline solution (Na(+)-loaded CCD) or in a sucrose solution (control CCD) and then rewarmed for various time periods to allow pump recruitment to occur. The number of pumps in the membrane was determined by specific [3H]ouabain binding; Nai was measured using 22Na. A rise in Nai induced a threefold increase in the number of basolateral pumps, which was fully achieved within 1-2 min. This pump recruitment was reversible within 15 min after restoration of low Nai. It was unaffected by inhibitors of cytoskeleton and Ca2+ ionophore A 23187. The blocker of the Na(+)-H+ antiporter, amiloride, did not prevent it. The protein kinase C activator, phorbol 12-myristate 13-acetate, did not induce it in the absence of Na+. We conclude that Nai is a major determinant of pump recruitment and/or activation, which occurs over a very short period of time. It may constitute a rapid adaptative response to an increase in the cell Na+ load.
Collapse
Affiliation(s)
- N Coutry
- Institut National de la Santé et de la Recherche Médicale Unité 246, Paris, France
| | | | | | | | | |
Collapse
|
12
|
Kikeri D, Sun A, Zeidel ML, Hebert SC. Cellular NH4+/K+ transport pathways in mouse medullary thick limb of Henle. Regulation by intracellular pH. J Gen Physiol 1992; 99:435-61. [PMID: 1588302 PMCID: PMC2216601 DOI: 10.1085/jgp.99.3.435] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Fluorescence and electrophysiological methods were used to determine the effects of intracellular pH (pHi) on cellular NH4+/K+ transport pathways in the renal medullary thick ascending limb of Henle (MTAL) from CD1 mice. Studies were performed in suspensions of MTAL tubules (S-MTAL) and in isolated, perfused MTAL segments (IP-MTAL). Steady-state pHi measured using 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) averaged 7.42 +/- 0.02 (mean +/- SE) in S-MTAL and 7.26 +/- 0.04 in IP-MTAL. The intrinsic cellular buffering power of MTAL cells was 29.7 +/- 2.4 mM/pHi unit at pHi values between 7.0 and 7.6, but below a pHi of 7.0 the intrinsic buffering power increased linearly to approximately 50 mM/pHi unit at pHi 6.5. In IP-MTAL, NH4+ entered cells across apical membranes via both Ba(2+)-sensitive pathway and furosemide-sensitive Na+:K+(NH4+):2Cl- cotransport mechanisms. The K0.5 and maximal rate for combined apical entry were 0.5 mM and 83.3 mM/min, respectively. The apical Ba(2+)-sensitive cell conductance in IP-MTAL (Gc), which reflects the apical K+ conductance, was sensitive to pHi over a pHi range of 6.0-7.4 with an apparent K0.5 at pHi approximately 6.7. The rate of cellular NH4+ influx in IP-MTAL due to the apical Ba(2+)-sensitive NH4+ transport pathway was sensitive to reduction in cytosolic pH whether pHi was changed by acidifying the basolateral medium or by inhibition of the apical Na+:H+ exchanger with amiloride at a constant pHo of 7.4. The pHi sensitivities of Gc and apical, Ba(2+)-sensitive NH4+ influx in IP-MTAL were virtually identical. The pHi sensitivity of the Ba(2+)-sensitive NH4+ influx in S-MTAL when exposed to (apical+basolateral) NH4Cl was greater than that observed in IP-MTAL where NH4Cl was added only to apical membranes, suggesting an additional effect of intracellular NH4+/NH3 on NH4+ influx. NH4+ entry via apical Na+:K+ (NH4+):2Cl- cotransport in IP-MTAL was somewhat more sensitive to reductions in pHi than the Ba(2+)-sensitive NH4+ influx pathway; NH4+ entry decreased by 52.9 +/- 13.4% on reducing pHi from 7.31 +/- 0.17 to 6.82 +/- 0.14. These results suggest that pHi may provide a negative feedback signal for regulating the rate of apical NH4+ entry, and hence transcellular NH4+ transport, in the MTAL. A model incorporating these results is proposed which illustrates the role of both pHi and basolateral/intracellular NH4+/NH3 in regulating the rate of transcellular N H4+ transport in the MTAL.
Collapse
Affiliation(s)
- D Kikeri
- Harvard Center for the Study of Kidney Disease, Harvard Medical School
| | | | | | | |
Collapse
|
13
|
Husted RF, Laplace JR, Stokes JB. Enhancement of electrogenic Na+ transport across rat inner medullary collecting duct by glucocorticoid and by mineralocorticoid hormones. J Clin Invest 1990; 86:498-506. [PMID: 2384596 PMCID: PMC296752 DOI: 10.1172/jci114736] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We have investigated the effect of steroid hormones on Na+ transport by rat renal inner medullary collecting duct (IMCD) cells. These cells, grown on permeable supports in primary culture, grow to confluence and develop a transmonolayer voltage oriented such that the apical surface is negative with respect to the basal surface. The results of these experiments demonstrate that this voltage is predominantly (or exclusively) the result of electrogenic Na+ absorption. Na+ transport can be stimulated two- to fourfold by exposure to either dexamethasone or aldosterone (100 nM). Experiments using specific antagonists of the glucocorticoid and mineralocorticoid receptors indicate that activation of either receptor stimulates electrogenic Na+ transport; electroneutral Na+ transport is undetectable. Two other features of the IMCD emerge from these studies. (a) These cells appear to have the capacity to metabolize the naturally occurring glucocorticoid hormone corticosterone. (b) The capacity for K+ secretion is minimal and steroid hormones do not induce or stimulate conductive K+ secretion as they do in the cortical collecting duct.
Collapse
Affiliation(s)
- R F Husted
- Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242
| | | | | |
Collapse
|
14
|
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
|
15
|
Oberleithner H, Kersting U, Silbernagl S, Steigner W, Vogel U. Fusion of cultured dog kidney (MDCK) cells: II. Relationship between cell pH and K+ conductance in response to aldosterone. J Membr Biol 1989; 111:49-56. [PMID: 2810351 DOI: 10.1007/bf01869208] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We have chosen the MDCK cell line to investigate aldosterone action on H+ transport and its role in regulating cell membrane K+ conductance (GKm). Cells grown in a monolayer respond to aldosterone indicated by the dose-dependent formation of domes and by the alkalinization of the dome fluid. The pH sensitivity of the plasma membrane K+ channels was tested in "giant cells" fused from individual MDCK cells. Cytoplasmic pH (pHi) and GKm were measured simultaneously while the cell interior was acidified gradually by an extracellular acid load. We found a steep sigmoidal relationship between pHi and GKm (Hill coefficient 4.4 +/- 0.4), indicating multiple H+ binding sites at a single K+ channel. Application of aldosterone increased pHi within 120 min from 7.22 +/- 0.04 to 7.45 +/- 0.02 and from 7.15 +/- 0.03 to 7.28 +/- 0.02 in the absence and presence of the CO2/HCO-3 buffer system, respectively. We conclude that the hormone-induced cytoplasmic alkalinization in the presence of CO2/HCO-3 is limited by the increased activity of a pHi-regulating HCO-3 extrusion system. Since GKm is stimulated half-maximally at the pHi of 7.18 +/- 0.04, internal H+ ions could serve as an effective intracellular signal for the regulation of transepithelial K+ flux.
Collapse
Affiliation(s)
- H Oberleithner
- Department of Physiology, University of Würzburg, Federal Republic of Germany
| | | | | | | | | |
Collapse
|
16
|
Chapter 10 Involvement of Na+,K+-ATPase in Antinatriuretic Action of Mineralocorticoids in Mammalian Kidney. CURRENT TOPICS IN MEMBRANES AND TRANSPORT 1989. [DOI: 10.1016/s0070-2161(08)60014-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
|
17
|
Oberleithner H, Kersting U, Hunter M. Cytoplasmic pH determines K+ conductance in fused renal epithelial cells. Proc Natl Acad Sci U S A 1988; 85:8345-9. [PMID: 2460867 PMCID: PMC282426 DOI: 10.1073/pnas.85.21.8345] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The mineralocorticoid hormone aldosterone maintains acid-base balance and K+ homeostasis by regulating H+ and K+ secretory mechanisms in kidney epithelial cells. We have shown recently in the amphibian distal nephron that aldosterone activates a Na+/H+ exchange system in the luminal cell membrane, thus leading to transepithelial H+ secretion and cytoplasmic alkalinization. Since H+ secretory fluxes were paralleled by K+ secretion, it was postulated that the hormone-induced increase of intracellular pH activates the luminally located K+ channels. In "giant" cells fused from individual cells of the distal nephron, we measured simultaneously cytoplasmic pH and cell membrane K+ conductance during acidification of the cell cytoplasm. The experiments show that cell membrane K+ conductance is half-maximal at an intracellular pH of 7.42 and that a positive cooperative interaction exists between K+-channel proteins and H+ (Hill coefficient = 6.5). Moreover, the cellular K+ conductance is most sensitive to cytoplasmic pH in the range modified by aldosterone. This supports the hypothesis that intracellular H+ activity, regulated by the Na+/H+ exchanger, serves as the signal to couple aldosterone-induced K+ secretory flux to H+ secretion in renal tubules.
Collapse
Affiliation(s)
- H Oberleithner
- Department of Physiology, University of Würzburg, Federal Republic of Germany
| | | | | |
Collapse
|
18
|
|
19
|
Minuth WW, Steckelings U, Gross P. Methylation of cytosolic proteins may be a possible biochemical pathway of early aldosterone action in cultured renal collecting duct cells. Differentiation 1987; 36:23-34. [PMID: 3446560 DOI: 10.1111/j.1432-0436.1987.tb00178.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The common model of aldosterone-dependent sodium transport is that the hormone increases sodium transport during the "early" and "late" response phases by inducing specific proteins (AIPs). However, in actual biochemical studies, AIPs were mostly detected 6-24 h after aldosterone application. Regarding the physiological early response phase, this implies temporal dissociation of the physiological and biochemical events. The discrepancy raises the question as to whether other biochemical events, such as protein modifications, may be involved in addition to the novo protein synthesis. Labelling of cultured renal collecting duct epithelia for 1-5 h with a radioactive methylgroup donor, S-adenosyl methionine (SAM), following tissue fractionation, resulted in progressive methylations of specific cytosolic proteins. Aldosterone-dependent methylations increased consistently with time, and accounted for a 60% increase in total cytosolic protein content as compared to controls after 5 h labelling. The different methylated proteins showed a molecular weight of 220, 97 and 75 kd and comprised groups of proteins with an isoelectric point of 5.1-5.7 and 6.0-7.5. Methylation of identical proteins was obtained by incubation of the epithelia with unlabelled SAM instead of aldosterone. SAM-induced as well as aldosterone-induced methylation of proteins with an isoelectric point of 6.0-7.5 could be inhibited by the methylation inhibitor S-adenosylhomocysteine. The results indicate that aldosterone may influence the SAM cycle in cultured collecting-duct epithelia during increase of the Na+-transport.
Collapse
Affiliation(s)
- W W Minuth
- Institute of Anatomy I, University of Heidelberg, Federal Republic of Germany
| | | | | |
Collapse
|