Abstract P244: Role of the Na-H Exchanger Regulatory Factor 1 (NHERF1) in Hypertension of Aging Animals

Hypertension ◽  
2015 ◽  
Vol 66 (suppl_1) ◽  
Author(s):  
Sathnur Pushpakumar ◽  
Corey J Ketchem ◽  
Michelle T Barati ◽  
Utpal Sen ◽  
Pedro J Jose ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Sodium Intake ◽  
Dietary Sodium ◽  
Brown Norway ◽  
Proximal Tubule Cells ◽  
Left Femoral Artery ◽  
Old Rats ◽  
Dopamine Signaling ◽  
Old Mice

Aging animals develop hypertension when challenged with high salt diet due, in part, to desensitization of dopamine receptors (DR) in renal proximal tubules (RPT). We have demonstrated that NHERF1 associates with DR1 and Na-K ATPase (NKA) and is important for regulation of NKA in RPT. Preliminary data showed loss of NHERF1 expression in 22m old F344 rats. We hypothesized that loss of NHERF1 results in increased blood pressure (BP) and lack of natriuretic response to dopamine (DA) in aging animals. To address this hypothesis, Fischer Brown Norway (FBN) rats (1m, 4m, 12m, and 24m old) were fed diet containing 1% or 8% NaCl for one week and, BP was measured in anesthetized animals using an indwelling left femoral artery catheter. 8% NaCl did not increase BP in 1m or 4 month old rats. By contrast, 8% NaCl diet increased BP in 12m (84.3±3.5 vs 90.8±2.36) and 24m (73.5±7.58 vs 104±1.6) old animals. To determine if lack of NHERF1 is responsible for the increase in BP, we measured BP in 12 m old WT and NHERF1 KO mice. By contrast to WT mice, 8% NaCl diet did not increase BP in NHERF1 KO mice (84±4.9 vs 96.5±3.56 (WT) and 78.2±3.89 vs 81.8±9.2 (NHERF1 KO mice)). To confirm that NHERF1 is required for DA-mediated inhibition of NKA, NKA activity in primary proximal tubule cells (PTC) from young and old mice in culture was measured in the presence or absence of DA. DA decreased NKA activity in PTC from young animals (67.2±3.8 vs 32.7±5.3) but not in PTC from old animals. Transfection of NHERF1 restored NKA regulation by DA in PTC from old rats (58.4±4.2 vs 64.4±4.3 (in untransfected cells) 54.2±3.8 vs 31.1±3.4 (in NHERF1 transfected cells)). We conclude that NHERF1 regulates DA-mediated proximal tubule sodium handling; however, other factors modulate BP response to dietary sodium intake in young and old animals. The contribution of NHERF1 and dopamine signaling to sodium homeostasis requires further study.

scholarly journals Expression and role of serum and glucocorticoid-regulated kinase 2 in the regulation of Na+/H+ exchanger 3 in the mammalian kidney

2010 ◽  
Vol 299 (6) ◽  
pp. F1496-F1506 ◽  
Author(s):  
Alan C. Pao ◽  
Aditi Bhargava ◽  
Francesca Di Sole ◽  
Raymond Quigley ◽  
Xinli Shao ◽  
...  
Keyword(s):  
In Situ Hybridization ◽  
Proximal Tubule ◽  
Cell Surface Expression ◽  
Thick Ascending Limb ◽  
Proximal Tubule Cells ◽  
Mammalian Kidney ◽  
Tubule Cells ◽  
Exchange Activity

Serum and glucocorticoid-regulated kinase 2 (sgk2) is 80% identical to the kinase domain of sgk1, an important mediator of mineralocorticoid-regulated sodium (Na+) transport in the distal nephron of the kidney. The expression pattern and role in renal function of sgk2 are virtually uncharacterized. In situ hybridization and immunohistochemistry of rodent kidney coupled with real-time RT-PCR of microdissected rat kidney tubules showed robust sgk2 expression in the proximal straight tubule and thick ascending limb of the loop of Henle. Sgk2 expression was minimal in distal tubule cells with aquaporin-2 immunostaining but significant in proximal tubule cells with Na+/H+ exchanger 3 (NHE3) immunostaining. To ascertain whether mineralocorticoids regulate expression of sgk2 in a manner similar to sgk1, we examined sgk2 mRNA expression in the kidneys of adrenalectomized rats treated with physiological doses of aldosterone together with the glucocorticoid receptor antagonist RU486. Northern blot analysis and in situ hybridization showed that, unlike sgk1, sgk2 expression in the kidney was not altered by aldosterone treatment. Based on the observation that sgk2 is expressed in proximal tubule cells that also express NHE3, we asked whether sgk2 regulates NHE3 activity. We heterologously expressed sgk2 in opossum kidney (OKP) cells and measured Na+/H+ exchange activity by Na+-dependent cell pH recovery. Constitutively active sgk2, but not sgk1, stimulated Na+/H+ exchange activity by >30%. Moreover, the sgk2-mediated increase in Na+/H+ exchange activity correlated with an increase in cell surface expression of NHE3. Together, these results suggest that the pattern of expression, regulation, and role of sgk2 within the mammalian kidney are distinct from sgk1 and that sgk2 may play a previously unrecognized role in the control of transtubular Na+ transport through NHE3 in the proximal tubule.

Influence of Na+ intake on dopamine-induced inhibition of renal cortical Na(+)-K(+)-ATPase

1990 ◽  
Vol 258 (1) ◽  
pp. F52-F60 ◽  
Author(s):  
I. Seri ◽  
B. C. Kone ◽  
S. R. Gullans ◽  
A. Aperia ◽  
B. M. Brenner ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Sodium Intake ◽  
Dietary Sodium ◽  
Acid Decarboxylase ◽  
Proximal Tubule Cell ◽  
Maximal Velocity ◽  
Tubule Cell ◽  
Amino Acid Decarboxylase ◽  
Cell Cytosol ◽  
In Cells

The enzyme L-amino acid decarboxylase (L-AADC), found in abundance in rat proximal tubule cell cytosol, converts L-dopa to dopamine. Dopamine, in turn, suppresses proximal tubule sodium transport by inhibiting Na(+)-K(+)-ATPase activity. We sought to determine whether changes in dietary sodium intake in rats lead to adaptation of dopamine formation and dopamine-induced Na(+)-K(+)-ATPase inhibition. In rats on a high-salt (HS) diet, the maximal velocity (Vmax) of renal cortical L-AADC was 78 +/- 19% higher than that in rats on a low-salt (LS) diet. The Michaelis constant (Km) of the enzyme remained unchanged. In renal cortical tubule cell suspensions the L-dopa-induced inhibition of ouabain-sensitive oxygen consumption (QO2) was significantly greater in rats on HS diet than in rats on LS diet. Furthermore, L-dopa completely inhibited the nystatin-induced rise in QO2 in the HS but not in the LS group. Carbidopa, an inhibitor of L-AADC, abolished the L-dopa-induced inhibition of nystatin-stimulated QO2 in cells from HS rats and was without significant effect in cells from LS rats. L-Dopa-stimulated K+ efflux was greater in cells from HS rats at 28 +/- 1 nmol.min-1.mg protein-1, compared with 7 +/- 6 nmol.min-1.ng protein-1 in cells from LS rats. By contrast, ouabain-stimulated K+ efflux did not differ between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased fluid absorption and cell volume in isolated rabbit proximal straight tubules after in vivo DOCA administration

1981 ◽  
Vol 241 (5) ◽  
pp. F502-F508 ◽  
Author(s):  
M. A. Knepper ◽  
M. B. Burg
Keyword(s):  
Proximal Tubule ◽  
Cell Volume ◽  
Fluid Transport ◽  
Sodium Intake ◽  
Plasma Concentrations ◽  
Dietary Sodium ◽  
Fluid Absorption ◽  
Direct Stimulation ◽  
Stimulation Of

To investigate whether mineralocorticoids affect the intrinsic capacity of the proximal tubule to absorb sodium and fluid, rabbits were chronically treated a number of ways to systematically vary plasma concentrations of mineralocorticoid hormones. The rate of fluid absorption and tubule dimensions were measured in superficial S2 segments from these rabbits. Chronic administration of deoxycorticosterone acetate (DOCA) was associated with a 67% increase in fluid absorption and a 29% increase in cell volume per unit tubule length. However, neither adrenalectomy nor low sodium diet significantly affected either fluid absorption or cell volume. Furthermore, marked dietary sodium restriction prevented the response to DOCA. We conclude that the DOCA-induced increases in fluid absorption and cell volume do not result from a direct stimulation of the proximal tubular cells by the steroid but more likely are responses to systemic effects of DOCA administration that are dependent on the level of sodium intake. Thus, we find no evidence for a direct mineralocorticoid stimulation of sodium and fluid transport by the S2 portion of the proximal tubule.

Role of MAPK pathways in light chain-induced cytokine production in human proximal tubule cells

2003 ◽  
Vol 284 (6) ◽  
pp. F1245-F1254 ◽  
Author(s):  
Sule Sengul ◽  
Craig Zwizinski ◽  
Vecihi Batuman
Keyword(s):  
Proximal Tubule ◽  
Light Chain ◽  
Cytokine Production ◽  
Tubulointerstitial Injury ◽  
Proximal Tubule Cells ◽  
Mapk Pathways ◽  
Cytokine Responses ◽  
Tubule Cells ◽  
Human Proximal Tubule

We previously demonstrated that light chain (LC) endocytosis by human proximal tubule cells (PTCs) leads to production of cytokines through activation of NF-κB. Here, we examined the role of MAPK pathways in these responses using four species of myeloma LCs (κ1, κ2, κ3, and λ1) previously shown to induce cytokine production by PTCs. Among these, κ1-LC, which yielded the strongest cytokine responses, was selected for detailed studies. Activation of MAPKs was probed by Western blot analysis for the active kinases, ERK 1/2, JNK 1/2, and p38 in κ1-LC-exposed human PTCs. To evaluate the functional role of MAPKs in LC-induced cytokine responses, we tested the effects of U-0126, an ERK inhibitor; SP-600125, an inhibitor of JNK; SB-203580, a p38 inhibitor; and curcumin, a JNK-AP-1 inhibitor, all added to media before 4-h exposure to 1.5 mg/ml κ1-LC. IL-6 and monocyte chemotactic protein-1 (MCP-1) were determined by ELISA. Both LC and human serum albumin (HSA) activated ERK, although the HSA effect was weaker. κ1-LC stimulated all three MAPKs, although phosphorylation of ERK was more pronounced and sustained than others. Inhibitors of ERK, JNK, and p38 reduced LC-induced IL-6 and MCP-1 production. These findings suggest that activation of MAPKs plays a role in LC-induced cytokine responses in PTCs. Activation of MAPKs may be involved in cytokine responses induced by other proteins as well as LCs and may be pivotal in the pathophysiology of tubulointerstitial injury in proteinuric diseases.

Investigations into the causes of the rise in aldosterone secretion during haemorrhage Part I

1966 ◽  
Vol 250 (767) ◽  
pp. 243-276 ◽  
Keyword(s):  
Carotid Sinus ◽  
Surgical Stress ◽  
Sodium Intake ◽  
Significant Rise ◽  
Dietary Sodium ◽  
Aldosterone Secretion ◽  
Pituitary Glands ◽  
Acute Haemorrhage ◽  
Stimulation Of

The effect of haemorrhage on aldosterone secretion was studied in anaesthetized dogs with intact pituitary glands and kidneys subjected to the stress of adrenal vein cannulation. The following observations were made: Acute haemorrhage was followed by a significant rise in aldosterone secretion in about one half of the animals studied. In most of the remaining dogs, called non-reactors, premature stimulation of aldosterone secretion before the withdrawal of blood appeared to be the cause for the lack of response. This stimulation was traced in many instances to prolonged surgical ‘stress’, in others to incipient circulatory failure. Another reason for a high initial secretion rate of aldosterone was low dietary sodium intake continued for a week or more. Increase in aldosterone secretion after haemorrhage was unimpaired by sectioning the vagi or the splanchnic nerves, and by the absence of the proprioceptors of carotid sinus and thyro-carotid junction, or of liver, spleen and gastrointestinal tract. During haemorrhage there is secretion of medullary amines and anoxia develops. The effect of these factors on aldosterone secretion was tested by infusing adrenaline and noradrenaline in the splanchnotomized animal, and by carrying out exchange transfusions with plasma till the dog had lost 50 % of its red cells. Provided the initial aldosterone secretion was low enough, these procedures caused small rises in output of aldosterone, but constituted less effective stimuli than blood loss. Glucocorticoid secretion was in all animals maximal or near maximal and changed but little in the course of the experiments. The findings suggest that, in the intact dog, aldosterone secretion is influenced by a variety of factors, most of which act indirectly by releasing ACTH , or renin, or both. The role of ACTH and of renin as mediators of the action of haemorrhage on secretion of aldosterone will be studied in part II.

scholarly journals Role of insulin-like growth factor binding proteins in human post-nephrectomy proximal tubule cells

1998 ◽  
Vol 508 (2) ◽  
pp. 587-595 ◽  
Author(s):  
David W. Johnson ◽  
Heather J. Saunders ◽  
Michael J. Field ◽  
Carol A. Pollock
Keyword(s):  
Growth Factor ◽  
Proximal Tubule ◽  
Binding Proteins ◽  
Insulin Like Growth Factor ◽  
Proximal Tubule Cells ◽  
Factor Binding ◽  
Tubule Cells

Effects of apical membrane Cl(-)-formate exchange on cell volume in rabbit proximal tubule

1990 ◽  
Vol 258 (3) ◽  
pp. F530-F536 ◽  
Author(s):  
L. Schild ◽  
P. S. Aronson ◽  
G. Giebisch
Keyword(s):  
Proximal Tubule ◽  
Cell Volume ◽  
Apical Membrane ◽  
Cell Swelling ◽  
Volume Changes ◽  
Proximal Tubule Cells ◽  
Volume Increase ◽  
Tubule Lumen ◽  
Stimulation Of

We used real-time recordings of cell volume changes to test for the role of the Cl(-)-formate exchanger in mediating NaCl entry across the apical membrane of rabbit proximal tubule cells. In the absence of extracellular Cl-, 0.5 and 5 mM formate in the tubule lumen induced an increase in cell volume of 1 and 9%, respectively. Formate-induced cell swelling was reduced by alkalinizing the tubule lumen or by addition of luminal amiloride (2 mM), indicating that the increase in cell volume results from the intracellular accumulation of Na-formate via nonionic diffusion of formic acid in parallel with Na(+)-H+ exchange. The cell volume increase induced by 0.5 mM formate was potentiated (from 1 to 4%) by Cl-, as expected for a formate-mediated stimulation of NaCl uptake via parallel Cl(-)-formate exchange and Na(+)-H+ exchange across the apical membrane. By contrast, the cell volume increase induced by 5 mM formate was attenuated (from 9 to 4%) by Cl-. The attenuating effect of Cl- on formate-induced cell swelling required the operation of the apical membrane Cl(-)-formate exchanger. The effect of 1:1 Cl(-)-formate exchange to attenuate formate-induced cell swelling can be explained if the cell possesses a volume-activated anion exit pathway, most likely at the basolateral cell membrane, that is capable of mediating the efflux of Cl- but not formate from the cell.

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