Expression of 25-Hydroxyvitamin D3-1α-Hydroxylase in the Human Kidney

Abstract. The secosteroid hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plays a vital role in calcium metabolism, tissue differentiation, and normal bone growth. Biosynthesis of 1,25(OH)2D3 is catalyzed by the mitochondrial cytochrome P450 enzyme 25-hydroxyvitamin D3 1α-hydroxylase (1α-hydroxylase). Although activity of this enzyme has been described in several tissues, the kidneys are recognized to be the principal site of 1,25(OH)2D3 production. To date, enzyme activity studies using vitamin D-deficient animals have suggested that 1α-hydroxylase is expressed exclusively in proximal convoluted tubules. With the recent cloning of 1α-hydroxylase, specific cRNA probes and in-house polyclonal antiserum have been used to determine the distribution of 1α-hydroxylase along the human nephron. Immunohistochemistry and in situ hybridization studies indicated strong expression of 1α-hydroxylase protein and mRNA in the distal convoluted tubule, the cortical and medullary part of the collecting ducts, and the papillary epithelia. Lower expression was observed along the thick ascending limb of the loop of Henle and Bowman's capsule. Weaker and more variable expression of 1α-hydroxylase protein and mRNA was seen in proximal convoluted tubules, and no expression was observed in glomeruli or vascular structures. These data show for the first time the distribution of 1α-hydroxylase expression in normal human kidney. In contrast to earlier enzyme activity studies conducted in vitamin D-deficient animals, our data indicate that the distal nephron is the predominant site of 1α-hydroxylase expression under conditions of vitamin D sufficiency.

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Development of solute transport in rabbit proximal tubule. III. Na-K-ATPase activity

AJP Renal Physiology ◽

10.1152/ajprenal.1984.246.6.f845 ◽

1984 ◽

Vol 246 (6) ◽

pp. F845-F852 ◽

Cited By ~ 5

Author(s):

G. J. Schwartz ◽

A. P. Evan

Keyword(s):

Enzyme Activity ◽

Atpase Activity ◽

Proximal Tubule ◽

Atp Hydrolysis ◽

Glucose Absorption ◽

Collagenase Treatment ◽

The Mean ◽

Convoluted Tubules ◽

Interim Period ◽

Proximal Convoluted Tubules

HCO-3 transport (JHCO-3) in early juxtamedullary proximal convoluted tubules isolated from infant rabbits during the 1st 3 wk of life is about one-third that in tubules obtained from adults. A rapid increase in transport ensues during wk 4 through 6, so that near-mature levels are attained by the end of this time. Because the pattern for development of glucose absorption was similar and because both HCO-3 and glucose absorption are driven by the lumen-to-cell Na+ flux, the activity of Na-K-ATPase (the Na+-extruding pump) was considered to be a critical mediator. A kinetic microassay (which couples ATP hydrolysis to NADH oxidation) allowed the measurement of Na-K-ATPase and ouabain-insensitive ATPase on the same tubular segment. Three to nine early juxtamedullary proximal convoluted tubules were obtained after collagenase treatment of the kidney and four to six rabbits were studied at each week of life. The mean activity of Na-K-ATPase during the 1st wk of life was 44.5 +/- 3.5 pmol X min-1 X mm-1, one-third of the adult level. During an interim period of development (2-6 wk), enzyme activity gradually reached 60% of adult levels (76.3 +/- 3.0 at 6 wk), while transport of HCO-3 and glucose, studied previously in other animals, attained mature rates. Only in the 7th wk did the enzyme activity reach that of the adult (106.8 +/- 6.8 in wk 7 vs. 128.4 +/- 14.0 in adult rabbits).(ABSTRACT TRUNCATED AT 250 WORDS)

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Nephron-specific expression of components of the renin–angiotensin–aldosterone system in the mouse kidney

Journal of the Renin-Angiotensin-Aldosterone System ◽

10.1177/1470320311432184 ◽

2012 ◽

Vol 13 (1) ◽

pp. 46-55 ◽

Cited By ~ 7

Author(s):

Stephan W Reinhold ◽

Bernd Krüger ◽

Caroline Barner ◽

Flavius Zoicas ◽

Martin C Kammerl ◽

...

Keyword(s):

Mouse Kidney ◽

Proximal Tubules ◽

Thick Ascending Limb ◽

Specific Expression ◽

Renin Angiotensin Aldosterone System ◽

Renin Angiotensin ◽

Nephron Segments ◽

Specific Distribution ◽

Convoluted Tubules ◽

Proximal Convoluted Tubules

Introduction: The renin–angiotensin–aldosterone system (RAAS) plays an integral role in the regulation of blood pressure, electrolyte and fluid homeostasis in mammals. The capability of the different nephron segments to form components of the RAAS is only partially known. This study therefore aimed to characterize the nephron-specific expression of RAAS components within the mouse kidney. Materials and methods: Defined nephron segments of adult C57B/16 mice were microdissected after collagenase digestion. The gene expression of renin, angiotensinogen (AGT), angiotensin-converting enzyme (ACE), angiotensin II receptors 1a (AT1a), 1b (AT1b), and 2 (AT2) was assessed by reverse transcriptase polymerase chain reaction (RT-PCR). Results: Renin mRNA was present in glomeruli, in proximal tubules, in distal convoluted tubules (DCT) and cortical collecting ducts (CCD). AGT mRNA was found in proximal tubules, descending thin limb of Henle’s loop (dTL) and in the medullary part of the thick ascending limb (mTAL). ACE mRNA was not detectable in microdissected mouse nephron segments. AT1a, AT1b and AT2 mRNA was detected in glomeruli and proximal convoluted tubules. Conclusions: Our data demonstrate a nephron-specific distribution of RAAS components. All components of the local RAAS – except ACE – are present in proximal convoluted tubules, emphasizing their involvement in sodium and water handling.

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Effects of furosemide or acetazolamide infusion on renal handling of lithium: a micropuncture study in rats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1993.264.1.r129 ◽

1993 ◽

Vol 264 (1) ◽

pp. R129-R134 ◽

Cited By ~ 3

Author(s):

R. Fransen ◽

W. H. Boer ◽

P. Boer ◽

E. J. Dorhout Mees ◽

H. A. Koomans

Keyword(s):

Concentration Ratio ◽

Thick Ascending Limb ◽

Renal Handling ◽

Pars Recta ◽

Micropuncture Study ◽

Convoluted Tubules ◽

Filtered Load ◽

Proximal Convoluted Tubules

Renal lithium (Li) handling was studied by micropuncture at the late proximal (LPT) and early distal (EDT) tubules in control rats and rats infused with furosemide (FUR) or acetazolamide (ACTZ). In control rats, the tubular fluid-to-plasma Li concentration ratio [(T/P)Li] at the LPT exceeded unity (1.05 +/- 0.02, P < 0.05). Some 25% of the filtered load (FL) of Li and water was reabsorbed in proportion between the LPT and the EDT, and consequently the (T/P)Li at the EDT (1.03 +/- 0.03) did not change. FUR inhibited Li reabsorption in the proximal convoluted tubules (PCT), by approximately 7% of the FL. Reabsorption of Li and water in the loop segment was also inhibited, virtually in proportion, by approximately 10% of the FL. These data suggest that FUR-sensitive Li reabsorption in the loop mainly takes place in the pars recta. However, a small increase in the (T/P)Li at the EDT (to 1.10 +/- 0.01) suggested inhibition of some Li transport (approximately 2% of the filtered load of Li) without water, most likely in the thick ascending limb (TAL). In the PCT, ACTZ reduced Li reabsorption by approximately 16% of its FL. Although it is likely that ACTZ also inhibited the pars recta, net Li reabsorption in the loop was not reduced. This suggests that TAL Li reabsorption can compensate for increased delivery.(ABSTRACT TRUNCATED AT 250 WORDS)

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Localization of the vitamin D-dependent calcium-binding protein in mammalian kidney

AJP Renal Physiology ◽

10.1152/ajprenal.1982.243.3.f243 ◽

1982 ◽

Vol 243 (3) ◽

pp. F243-F252 ◽

Cited By ~ 14

Author(s):

J. Roth ◽

D. Brown ◽

A. W. Norman ◽

L. Orci

Keyword(s):

Vitamin D ◽

Calcium Binding ◽

Binding Protein ◽

Collecting Duct ◽

Rat Kidney ◽

Protein A ◽

Human Kidney ◽

Calcium Binding Protein ◽

Medullary Collecting Duct ◽

Convoluted Tubules

The vitamin D-dependent calcium-binding protein (CaBP) was localized by immunocytochemistry in the rat and human kidney. In both species 80% of the cells lining the distal convoluted tubules contained CaBP. In the connecting segment and the initial collecting tubule of rat kidney, 50% of the cells was positive; in the outer medullary collecting duct only 15% was positive. In the human kidney, collecting ducts in medullary rays contained 50% positive cells, whereas in the rest of the medulla no positive cells were found. The CaBP-positive cells were identified as principal or clear cells by immunoelectron-microscopy, using the protein A-gold technique. Mitochondria-rich dark cells were negative. In principal cells, CaBP immunoreactive sites were found throughout the cytosol and the nuclear euchromatin. No preferential labeling of cellular membranes was found. The data show that CaBP-positive cells are present in tubular regions that are important in regulating the final excretion of calcium. However, the subcellular distribution of CaBP does not suggest a role in the initial transmembrane transport of Ca2+ but rather indicates an involvement in processes regulating intracellular calcium.

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