Role of CFTR and ClC-5 in modulating vacuolar H+-ATPase activity in kidney proximal tubule.
ABSTRACT It has been widely accepted that chloride ions moving along chloride channels act to dissipate the electrical gradient established by the electrogenic transport of H(+) ions performed by H(+)-ATPase into subcellular vesicles. Largely known in intracellular compartments, this mechanism is also important at the plasma membrane of cells from various tissues, including kidney. The present work was performed to study the modulation of plasma membrane H(+)-ATPase by chloride channels, in particular, CFTR and ClC-5 in kidney proximal tubule.
Using in vivo stationary microperfusion, it was observed that ATPase-mediated HCO(3)(-) reabsorption was significantly reduced in the presence of the Cl(-) channels inhibitor NPPB. This effect was confirmed in vitro by measuring the cell pH recovery rates after a NH(4)Cl pulse in immortalized rat renal proximal tubule cells, IRPTC. In these cells, even after abolishing the membrane potential with valinomycin, ATPase activity was seen to be still dependent on Cl(-). siRNA-mediated CFTR channels and ClC-5 chloride-proton exchanger knockdown significantly reduced H(+)-ATPase activity and V-ATPase B2 subunit expression.
These results indicate a role of chloride in modulating plasma membrane H(+)-ATPase activity in proximal tubule and suggest that both CFTR and ClC-5 modulate ATPase activity.
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ABSTRACT: Genetics plays an important role in establishing susceptibility to nephrolithiasis, although diet and other environmental factors make major contributions. In a small number of patients, the genetic causes of stones are more clearly established. Four of these hereditary diseases include primary hyperoxaluria, Dent disease, cystinuria, and adenine phosphoribosyltransferase deficiency, which results in 2,8-dihydroxyadenine stones. Patients with these disorders often experience recurring stones from early childhood, requiring frequent hospitalizations and procedures. They are at risk of kidney damage and chronic kidney disease. Because of their rarity, these four disorders are difficult to study and recognize. This in turn slows progress toward effective therapies and increases the risk of misdiagnosis or diagnosis late in the course of the disease. Therefore, patients may experience unnecessary and harmful treatments and accelerated loss of kidney function. In this article, we will review the pathogenesis, clinical presentation, diagnosis of and treatments for these four disorders.Clinical Reviews in Bone and Mineral Metabolism 01/2012; 10(1):2-18.
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ABSTRACT: The H(+) concentration in human blood is kept within very narrow limits, ∼40 nmol/L, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) generate a sufficient quantity of new HCO3(-) to compensate for the loss of HCO3(-) resulting from dietary metabolic H(+) loads and loss of HCO3(-) in the urea cycle; and (iii) excrete HCO3(-) (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ∼60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level. © 2014 American Physiological Society. Compr Physiol 4: 1737-1774, 2014.Comprehensive Physiology. 10/2014; 4(4):1737-74.
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ABSTRACT: Vacuolar ATPases (V-ATPases) are highly conserved proton pumps that regulate organelle pH. Epithelial luminal pH is also regulated by cAMP-dependent traffic of specific subunits of the V-ATPase complex from endosomes into the apical membrane. In the intestine, cAMP-dependent traffic of cystic fibrosis transmembrane conductance regulator (CFTR) channels and the sodium hydrogen exchanger (NHE3) in the brush border regulate luminal pH. V-ATPase was found to co-localize with CFTR in intestinal CFTR High Expresser (CHE) cells recently. Moreover, apical traffic of V-ATPase and CFTR in rat Brunner's glands was shown to be dependent on cAMP/PKA. These observations support a functional relationship between V-ATPase and CFTR in the intestine. The current study examined V-ATPase and CFTR distribution in intestines from wild-type, CFTR(-/-) mice and polarized intestinal CaCo-2 BBe cells following cAMP stimulation and inhibition of CFTR/V-ATPase function. Co- immunoprecipitation studies examined V-ATPase interaction with CFTR. The pH sensitive dye BCECF determined proton efflux and its dependence on V-ATPase/CFTR in intestinal cells. cAMP increased V-ATPase/CFTR co-localization in the apical domain of intestinal cells, and redistributed the V-ATPase Voa1 and Voa2 trafficking subunits from the basolateral membrane to the BBM. Voa1 and Voa2 subunits were localized to endosomes beneath the terminal web in untreated CFTR (-/-) intestine, but redistributed to the subapical cytoplasm following cAMP treatment. Inhibition of CFTR or V-ATPase significantly decreased pHi in cells, confirming their functional interdependence. These data establish that V-ATPase traffics into the brush border membrane to regulate proton efflux and this activity is dependent on CFTR in the intestine.AJP Cell Physiology 08/2013; · 3.71 Impact Factor