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Wen D.,85850 Nebraska Medical Center | Cornelius R.J.,85850 Nebraska Medical Center | Rivero-Hernandez D.,85850 Nebraska Medical Center | Yuan Y.,85850 Nebraska Medical Center | And 3 more authors.
Kidney International | Year: 2014

The large-conductance, calcium-activated BK-α/β4 potassium channel, localized to the intercalated cells of the distal nephron, mediates potassium secretion during high-potassium, alkaline diets. Here we determine whether BK-α/β4-mediated potassium transport is dependent on epithelial sodium channel (ENaC)-mediated sodium reabsorption. We maximized sodium-potassium exchange in the distal nephron by feeding mice a low-sodium, high-potassium diet. Wild-type and BK-β4 knockout mice were maintained on a low-sodium, high-potassium, alkaline diet or a low-sodium, high-potassium, acidic diet for 7-10 days. Wild-type mice maintained potassium homeostasis on the alkaline, but not acid, diet. BK-β4 knockout mice could not maintain potassium homeostasis on either diet. During the last 12 h of diet, wild-type mice on either a regular, alkaline, or an acid diet, or knockout mice on an alkaline diet, were administered amiloride (an ENaC inhibitor). Amiloride enhanced sodium excretion in all wild-type and knockout groups to similar values; however, amiloride diminished potassium excretion by 59% in wild-type but only by 33% in knockout mice on an alkaline diet. Similarly, amiloride decreased the trans-tubular potassium gradient by 68% in wild-type but only by 42% in knockout mice on an alkaline diet. Amiloride treatment equally enhanced sodium excretion and diminished potassium secretion in knockout mice on an alkaline diet and wild-type mice on an acid diet. Thus, the enhanced effect of amiloride on potassium secretion in wild-type compared to knockout mice on the alkaline diet clarify a BK- α/β4-mediated potassium secretory pathway in intercalated cells driven by ENaC-mediated sodium reabsorption linked to bicarbonate secretion. © 2014 International Society of Nephrology.

Mitra A.K.,85850 Nebraska Medical Center | Gao L.,85850 Nebraska Medical Center | Zucker I.H.,85850 Nebraska Medical Center
American Journal of Physiology - Cell Physiology | Year: 2010

It has been clearly established that increased circulating angiotensin II (ANG II) with concurrent upregulation of brain and peripheral ANG II type 1 receptors (AT1R) are important mediators in the pathophysiology of several diseases characterized by sympatho-excitation. In an effort to further understand the regulation of AT1R expression in neurons, we determined the role of sequential activation of the transcription factors nuclear factor-κB (NF-κB) and Ets-like protein 1 (Elk-1) in AT 1R upregulation. We used CATH.a neurons as our neuronal cell model. Cells were treated with ANG II (100 nM) over a preset time course. Following ANG II activation, there was a temporal increase in the p65 subunit of NF-κB that was observed at 30 min, peaked at 1 h, and was sustained up to 24 h. There was a concomitant decrease of IκB and increased IκK expression. We also observed an increase in AT1R expression which followed the temporal increase of NF-κB. The activation of NF-κB was blocked by using the inhibitors parthenolide or p65 small interfering RNA (siRNA) which both led to a decrease in AT1R expression. The expression of Elk-1 was upregulated over a time period following ANG II activation and was decreased following NF-κB inhibition. p65-DNA binding was assessed using electrophoretic mobility shift assay, and it was shown that there was a time-dependent increased binding that was inhibited by means of parthenolide pretreatment or siRNA-mediated p65 gene silencing. Therefore, our results suggest a combined role for the transcription factors NF-κB and Elk-1 in the upregulation of AT1R in the CATH.a cell neuronal model. These data imply a positive feedback mechanism that may impact neuronal discharge sensitivity in response to ANG II. Copyright © 2010 the American Physiological Society.

Holtzclaw J.D.,85850 Nebraska Medical Center | Liu L.,85850 Nebraska Medical Center | Grimm P.R.,85850 Nebraska Medical Center | Sansom S.C.,85850 Nebraska Medical Center
American Journal of Physiology - Renal Physiology | Year: 2010

Large-conductance, calcium-activated potassium channels (BK) are expressed in principal cells (PC) and intercalated cells (IC) in mammalian nephrons as BK-α/β1 and BK-α/β4, respectively. IC, which protrude into the lumens of tubules, express substantially more BK than PC despite lacking sufficient Na-K-ATPase to support K secretion. We previously showed in mice that IC exhibit size reduction when experiencing high distal flows induced by a high-K diet. We therefore tested the hypothesis that BK-α/β4 are regulators of IC volume via a shear stress (τ)-induced, calcium-dependent mechanism, resulting in a reduction in intracellular K content. We determined by Western blot and immunocytochemical analysis that C11-Madin-Darby canine kidney cells contained a predominance of BK-α/β4. To determine the role of BK-α/β4 in τ-induced volume reduction, we exposed C11 cells to τ and measured K efflux by flame photometry and cell volume by calcein staining, which changes inversely to cell volume. With 10 dynes/cm2, calcein intensity significantly increased 39% and monovalent cationic content decreased significantly by 37% compared with static conditions. Furthermore, the shear-induced K loss from C11 was abolished by the reduction of extracellular calcium, addition of 5 mM TEA, or BK-β4 small interfering (si) RNA, but not by addition of nontarget siRNA. These results show that BK-α/β4 plays a role in shear-induced K loss from IC, suggesting that BK-α/β4 regulate IC volume during high-flow conditions. Furthermore, these results support the use of C11 cells as in vitro models for studying BK-related functions in IC of the kidney. Copyright © 2010 the American Physiological Society.

Arrick D.M.,85850 Nebraska Medical Center | Mayhan W.G.,85850 Nebraska Medical Center
Microcirculation | Year: 2010

Objective: Endothelin-1 has been implicated in the pathogenesis of many cardiovascular-related diseases, including diabetes. The goal of this study was to examine the influence of endothelin-1 receptors (ETA) in impaired responses of cerebral (pial) arterioles in type-1 diabetic rats. Methods: We measured responses of cerebral arterioles in non-diabetic rats to endothelial nitric oxide synthase (eNOS)-dependent (ADP), neuronal nitric oxide synthase (nNOS)-dependent (N-methyl-d-aspartic acid [NMDA]) and NOS-independent (nitroglycerin) agonists before and during application of BQ-123, an ET A receptor antagonist. In addition, we harvested brain tissue from non-diabetic and diabetic rats to measure the production of superoxide anion under basal conditions and during inhibition of ETA receptors. Results: We found that diabetes specifically impaired eNOS- and nNOS-dependent reactivity of cerebral arterioles, but did not alter NOS-independent vasodilation. In addition, while BQ-123 did not alter responses in non-diabetic rats, BQ-123 restored impaired eNOS- and nNOS-dependent vasodilation in diabetic rats. Further, superoxide production was higher in brain tissue from diabetic rats compared with non-diabetic rats under basal conditions and BQ-123 decreased basal production of superoxide in diabetic rats. Conclusion: We suggest that activation of ETA receptors during type-1 diabetes mellitus plays an important role in impaired eNOS- and nNOS-dependent dilation of cerebral arterioles. © 2010 John Wiley & Sons Ltd.

PubMed | 85850 Nebraska Medical Center
Type: Journal Article | Journal: Current vascular pharmacology | Year: 2014

The mechanisms underlying initiation and progression of diabetic nephropathy are not well understood, despite the fact that diabetes represents the chief underlying cause of end-stage renal disease. The onset of diabetic hyperglycemia is now known to evoke functional alterations in the renal microvasculature, glomeruli and tubular epithelium. Although the scope of these effects is not yet fully recognized, the renal vascular dysfunction evident early after onset of T1D likely encompasses impaired electromechanical coupling in preglomerular vascular smooth muscle and altered interactions between tubular transport and vascular function. These changes, which arise in environment conducive to oxidative stress and inflammation, are thought to either initiate or facilitate the eventual development of diabetic nephropathy in susceptible individuals.

PubMed | 85850 Nebraska Medical Center
Type: Journal Article | Journal: Hypertension (Dallas, Tex. : 1979) | Year: 2014

Cheyne-Stokes respiration and cardiac arrhythmias are associated with increased morbidity and mortality in patients with chronic heart failure (CHF). Enhanced carotid body chemoreflex (CBC) sensitivity is associated with these abnormalities in CHF. Reduced carotid body (CB) nitric oxide and nitric oxide synthase (NOS) levels play an important role in the enhanced CBC. In other disease models, Simvastatin (statin) treatment increases endothelial NOS, in part, by increasing Krppel-like Factor 2 expression. We hypothesized that statin treatment would ameliorate enhanced CBC sensitivity as well as increased respiratory variability, apnea/hypopnea index, and arrhythmia index, in a rodent model of CHF. Resting breathing pattern, cardiac rhythm, and the ventilatory and CB chemoreceptor afferent responses to hypoxia were assessed in rats with CHF induced by coronary ligation. CHF was associated with enhanced ventilatory and CB afferent responses to hypoxia as well as increased respiratory variability, apnea/hypopnea index, and arrhythmia index. Statin treatment prevented the increases in CBC sensitivity and the concomitant increases in respiratory variability, apnea/hypopnea index, and arrhythmia index. Krppel-like Factor 2 and endothelial NOS protein were decreased in the CB and nucleus tractus solitarii of CHF animals, and statin treatment increased the expression of these proteins. Our findings demonstrate that the increased CBC sensitivity, respiratory instability, and cardiac arrhythmias observed in CHF are ameliorated by statin treatment and suggest that statins may be an effective treatment for Cheyne-Stokes respiration and arrhythmias in patient populations with high chemoreflex sensitivity.

PubMed | 85850 Nebraska Medical Center
Type: Journal Article | Journal: Journal of applied physiology (Bethesda, Md. : 1985) | Year: 2010

Our goal was to determine whether exercise training (ExT) alleviates impaired nitric oxide synthase (NOS)-dependent dilation of pial arterioles during chronic exposure to nicotine. We measured dilation of cerebral (pial) arterioles in sedentary and exercised control and nicotine-treated (2 mgkg(-1)day(-1) for 4 wk via an osmotic minipump) rats to an endothelial NOS (eNOS)-dependent (ADP), a neuronal NOS (nNOS)-dependent [N-methyl-D-aspartic acid (NMDA)], and a NOS-independent (nitroglycerin) agonist. In addition, we harvested brain tissue from sedentary and exercised control and nicotine-treated rats to measure the production of superoxide anion and measured superoxide dismutase-1 (SOD-1) protein in cerebral microvessels using Western blot. We found that eNOS-and nNOS-dependent, but not NOS-independent, vasodilation was impaired in nicotine-treated compared with control rats. In addition, the production of superoxide anion (lucigenin chemiluminescence) was increased, and SOD-1 protein decreased, in rats treated with nicotine compared with control rats. Further, although ExT did not significantly affect eNOS- or nNOS-dependent vasodilation in control rats, ExT restored impaired eNOS- and nNOS-dependent responses in nicotine-treated rats. In addition, the increase in superoxide anion production observed in nicotine-treated rats was reduced by ExT, and SOD-1 protein was increased in nicotine-treated rats by ExT. We suggest that ExT restores impaired NOS-dependent dilation of pial arterioles during chronic exposure to nicotine by a mechanism related to the formation of superoxide anion.

PubMed | 85850 Nebraska Medical Center
Type: Journal Article | Journal: American journal of physiology. Renal physiology | Year: 2013

In the distal nephron, the large-conductance Ca-activated K (BK) channel, comprised of a pore-forming- (BK-) and the BK-4 subunit, promotes K excretion when mice are maintained on a high-K alkaline diet (HK-alk). We examined whether BK-4 and the acid-base status regulate apical membrane expression of BK- in the cortical (CCD) and medullary collecting ducts (MCD) using immunohistochemical analysis (IHC) and Western blot. With the use of IHC, BK- of mice on acontrol diet localized mostly cytoplasmically in intercalated cells (IC) of the CCD and in the perinuclear region of both principle cells (PC) and IC of the MCD. HK-alk wild-type mice (WT), but not BK-4 knockout mice (4KO), exhibited increased apical BK- in both the CCD and MCD. When given a high-K acidic diet (HK-Cl), BK- expression increased but remained cytoplasmic in the CCD and perinuclear in the MCD of both WT and 4KO. Western blot confirmed that total BK- expression was enhanced by either HK-alk or HK-Cl but only increased in the plasma membrane with HK-alk. Compared with controls, mice drinking NaHCO3 water exhibited more apical BK- and total cellular BK-4. Spironolactone given to mice on HK-alk significantly reduced K secretion and decreased total cellular BK- but did not affect cellular BK-4 and apical BK-. Experiments with MDCK-C11 cells indicated that BK-4 stabilizes surface BK- by inhibiting degradation through a lysosomal pathway. These data suggest that aldosterone mediates a high-K-induced increase in BK- and urinary alkalinization increases BK-4 expression, which promotes the apical localization of BK-.

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