scholarly journals Roles of Akt and SGK1 in the Regulation of Renal Tubular Transport

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Nobuhiko Satoh ◽  
Motonobu Nakamura ◽  
Masashi Suzuki ◽  
Atsushi Suzuki ◽  
George Seki ◽  
...  
Keyword(s):  
Proximal Tubules ◽  
Kidney Cortex ◽  
Sodium Reabsorption ◽  
Serine Threonine Kinase ◽  
Akt Phosphorylation ◽  
Renal Transporters ◽  
Collecting Ducts ◽  
Tubular Transport ◽  
Renal Tubular Transport ◽  
Renal Tubular

A serine/threonine kinase Akt is a key mediator in various signaling pathways including regulation of renal tubular transport. In proximal tubules, Akt mediates insulin signaling via insulin receptor substrate 2 (IRS2) and stimulates sodium-bicarbonate cotransporter (NBCe1), resulting in increased sodium reabsorption. In insulin resistance, the IRS2 in kidney cortex is exceptionally preserved and may mediate the stimulatory effect of insulin on NBCe1 to cause hypertension in diabetes via sodium retention. Likewise, in distal convoluted tubules and cortical collecting ducts, insulin-induced Akt phosphorylation mediates several hormonal signals to enhance sodium-chloride cotransporter (NCC) and epithelial sodium channel (ENaC) activities, resulting in increased sodium reabsorption. Serum- and glucocorticoid-inducible kinase 1 (SGK1) mediates aldosterone signaling. Insulin can stimulate SGK1 to exert various effects on renal transporters. In renal cortical collecting ducts, SGK1 regulates the expression level of ENaC through inhibition of its degradation. In addition, SGK1 and Akt cooperatively regulate potassium secretion by renal outer medullary potassium channel (ROMK). Moreover, sodium-proton exchanger 3 (NHE3) in proximal tubules is possibly activated by SGK1. This review focuses on recent advances in understanding of the roles of Akt and SGK1 in the regulation of renal tubular transport.

scholarly journals Regulation of glomerular and proximal tubule renin mRNA by chronic changes in dietary NaCl

1997 ◽  
Vol 273 (6) ◽  
pp. F892-F898 ◽  
Author(s):  
Julia E. Tank ◽  
William L. Henrich ◽  
Orson W. Moe
Keyword(s):  
Proximal Tubule ◽  
Extracellular Fluid ◽  
Renin Angiotensin System ◽  
Proximal Tubules ◽  
Angiotensin System ◽  
Tubular Transport ◽  
Renin Mrna ◽  
Renal Tubular Transport ◽  
Polymerase Chain ◽  
Renal Tubular

Renal adaptations to chronic changes in dietary NaCl and extracellular fluid volume involve both glomerular and tubular mechanisms that result in preservation of glomerular filtration rate and modifications of renal tubular transport to secure external NaCl balance. Although the systemic renin-angiotensin system (RAS) mediates some of these responses, the possible contributions of local glomerular and proximal tubule RASs in these adaptations have not been examined. Thus, in this study, glomeruli and proximal tubules were microdissected from rats adapted to high (4.0%)-, normal (0.5%), or low (0.01%)-NaCl diets, and renin mRNA was measured using quantitative competitive reverse transcription-polymerase chain reaction. After 4 days of the diets, glomerular renin mRNA abundance was increased 100% by the low-NaCl diet ( P < 0.05) and suppressed 50% ( P < 0.01) by the high-NaCl diet compared with controls. Renin mRNA in proximal tubules was stimulated 230% ( P < 0.05) by the low-NaCl diet and tended to be suppressed (68% decrease, not significant) by the high-NaCl diet. When the high-NaCl diet was continued for 2 wk, proximal tubule renin mRNA was suppressed by 89% ( P < 0.05). This study provides evidence that glomerular and proximal tubule renin transcript levels are regulated by chronic changes in dietary NaCl, suggesting that local RASs contribute to the renal adaptations in response to chronic alterations in NaCl.

Renal tubular secretion of o-acetylaminohippurate

1962 ◽  
Vol 203 (5) ◽  
pp. 881-885 ◽  
Author(s):  
Gilbert H. Mudge ◽  
Keith Garlid ◽  
I. M. Weiner
Keyword(s):  
Tubular Secretion ◽  
Rabbit Kidney ◽  
Kidney Cortex ◽  
Renal Tubular Secretion ◽  
Kidney Slices ◽  
Tubular Transport ◽  
Clearance Studies ◽  
Renal Tubular Transport ◽  
Renal Tubular

Renal tubular transport of o-acetylaminohippurate (OAAH) was investigated because of previous reports that it differed from other hippurates by not undergoing tubular secretion. However, tubular secretion was readily demonstrable in nine clearance experiments in dogs. Secretion was decreased by succinate, 2,4 DNP, probenecid, hippurate, and Diodrast, substances all known to inhibit secretion of other hippurates. In vivo deacetylation was demonstrated. In slice system of rabbit kidney cortex, accumulation was also shown, but degree of uptake was complicated by deacetylation to OAH. Meta and para isomers did not undergo deacetylation. Both in clearance studies and in kidney slices, the transport of OAAH is qualitatively similar to other hippurates.

Carbonic anhydrase XII mRNA encodes a hydratase that is differentially expressed along the rabbit nephron

2003 ◽  
Vol 284 (2) ◽  
pp. F399-F410 ◽  
Author(s):  
George J. Schwartz ◽  
Anne M. Kittelberger ◽  
Richard H. Watkins ◽  
Michael A. O'Reilly
Keyword(s):  
Carbonic Anhydrase ◽  
Transmembrane Protein ◽  
Proximal Tubules ◽  
Rabbit Kidney ◽  
Kidney Cortex ◽  
Thick Ascending Limb ◽  
Basolateral Membranes ◽  
Collecting Ducts ◽  
Straight Tubules ◽  
Hydratase Activity

Membrane-bound carbonic anhydrase (CA) facilitates acidification in the kidney. Although most hydratase activity is considered due to CA IV, some in the basolateral membranes could be attributed to CA XII. Indeed, CA IV is glycosylphosphatidylinositol anchored, connoting apical polarization, but CA IV immunoreactivity has been detected on basolateral membranes of proximal tubules. Herein, we determined whether CA XII mRNA was expressed in acidifying segments of the rabbit nephron. The open reading frame of CA XII was sequenced from a rabbit kidney cortex cDNA library; it was 83% identical to human CA XII and coded for a 355-amino acid single-pass transmembrane protein. Northern blot analysis revealed an abundant 4.5-kb message in kidney cortex, medulla, and colon. By in situ hybridization, CA XII mRNA was expressed by proximal convoluted and straight tubules, cortical and medullary collecting ducts, and papillary epithelium. By RT-PCR, CA XII mRNA was abundantly expressed in cortical and medullary collecting ducts and thick ascending limb of Henle's loop; it was also expressed in proximal convoluted and straight tubules but not in glomeruli or S3 segments. FLAG-CA XII of ∼40 kDa expressed in Escherichia coli showed hydratase activity that was inhibited by 0.1 mM acetazolamide. Unlike CA IV, expressed CA XII activity was inhibited by 1% SDS, suggesting insufficient disulfide linkages to stabilize the molecule. Western blotting of expressed CA XII with two anti-rabbit CA IV peptide antibodies showed no cross-reactivity. Our findings indicate that CA XII may contribute to the membrane CA activity of proximal tubules and collecting ducts.

HOMEOSTATIC ADJUSTMENT IN THE RENAL TUBULAR TRANSPORT OF INORGANIC PHOSPHATE IN THE DOG

1955 ◽  
Vol 33 (1) ◽  
pp. 638-650 ◽  
Author(s):  
James G. Foulks
Keyword(s):  
Inorganic Phosphate ◽  
Renal Tubule ◽  
Phosphate Transport ◽  
Sodium Sulphate ◽  
Tubular Transport ◽  
Renal Tubular Transport ◽  
Transport Of Inorganic Phosphate ◽  
Renal Tubular ◽  
Filtered Load

By means of the infusion of small amounts of sodium sulphate it has been possible to elevate the filtered load of inorganic phosphate to the renal tubule in fasted dogs without the administration of exogenous phosphate. Under these circumstances, the reabsorption of phosphate remains virtually complete, even when filtered loads are reached which result in a substantial phosphaturia when phosphate has been administered. By comparing phosphate reabsorption and excretion in fasted animals, and in animals at various intervals after feeding, the existence of homeostatic adjustments in the renal tubular transport of inorganic phosphate has been demonstrated. The available evidence suggests that the intracellular disposition of phosphate itself may be an important factor in determining the rate of renal tubular phosphate transport at filtered loads in the physiological range. The limitations of the determination of the phosphate "Tm" as a device for studying homeostatic processes have been discussed.

AVP-stimulated nucleotide secretion in perfused mouse medullary thick ascending limb and cortical collecting duct

2009 ◽  
Vol 297 (2) ◽  
pp. F341-F349 ◽  
Author(s):  
Elvin Odgaard ◽  
Helle A. Praetorius ◽  
Jens Leipziger
Keyword(s):  
Collecting Duct ◽  
Tubular Secretion ◽  
Hormonal Control ◽  
Similar Response ◽  
Thick Ascending Limb ◽  
Cortical Collecting Duct ◽  
Medullary Thick Ascending Limb ◽  
Tubular Transport ◽  
Renal Tubular Transport ◽  
Renal Tubular

Extracellular nucleotides are local, short-lived signaling molecules that inhibit renal tubular transport via both luminal and basolateral P2 receptors. Apparently, the renal epithelium itself is able to release nucleotides. The mechanism and circumstances under which nucleotide release is stimulated remain elusive. Here, we investigate the phenomenon of nucleotide secretion in intact, perfused mouse medullary thick ascending limb (mTAL) and cortical collecting duct (CCD). The nucleotide secretion was monitored by a biosensor adapted to register nucleotides in the tubular outflow. Intracellular Ca2+ concentration ([Ca2+]i) was measured simultaneously in the biosensor cells and the renal tubule with fluo 4. We were able to identify spontaneous tubular nucleotide secretion in resting perfused mTAL. In this preparation, 10 nM AVP and 1-desamino-8-d-arginine vasopressin (dDAVP) induced robust [Ca2+]i oscillations, whereas AVP in the CCD induced large, slow, and transient [Ca2+]i elevations. Importantly, we identify that AVP/dDAVP triggers tubular secretion of nucleotides in the mTAL. After addition of AVP/dDAVP, the biosensor registered bursts of nucleotides in the tubular perfusate, corresponding to a tubular nucleotide concentration of ∼0.2–0.3 μM. A very similar response was observed after AVP stimulation of CCDs. Thus AVP stimulated tubular secretion of nucleotides in a burst-like pattern with peak tubular nucleotide concentrations in the low-micromolar range. We speculate that local nucleotide signaling is an intrinsic feedback element of hormonal control of renal tubular transport.

HOMEOSTATIC ADJUSTMENT IN THE RENAL TUBULAR TRANSPORT OF INORGANIC PHOSPHATE IN THE DOG

1955 ◽  
Vol 33 (4) ◽  
pp. 638-650 ◽  
Author(s):  
James G. Foulks
Keyword(s):  
Inorganic Phosphate ◽  
Renal Tubule ◽  
Phosphate Transport ◽  
Sodium Sulphate ◽  
Tubular Transport ◽  
Renal Tubular Transport ◽  
Transport Of Inorganic Phosphate ◽  
Renal Tubular ◽  
Filtered Load

By means of the infusion of small amounts of sodium sulphate it has been possible to elevate the filtered load of inorganic phosphate to the renal tubule in fasted dogs without the administration of exogenous phosphate. Under these circumstances, the reabsorption of phosphate remains virtually complete, even when filtered loads are reached which result in a substantial phosphaturia when phosphate has been administered. By comparing phosphate reabsorption and excretion in fasted animals, and in animals at various intervals after feeding, the existence of homeostatic adjustments in the renal tubular transport of inorganic phosphate has been demonstrated. The available evidence suggests that the intracellular disposition of phosphate itself may be an important factor in determining the rate of renal tubular phosphate transport at filtered loads in the physiological range. The limitations of the determination of the phosphate "Tm" as a device for studying homeostatic processes have been discussed.

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