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Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The isolated perfused tubule technique was used to study net acid transport in rat terminal inner medullary collecting duct (IMCD) segments. The stop-flow luminal pH [measured fluorometrically with the acidic form of the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein in the lumen] fell 0.35 units below the bath pH in tubules from control rats and 0.53 units below the bath in tubules from deoxycorticosterone-treated rats. Tubules from control rats absorbed bicarbonate and secreted ammonium against concentration gradients, although at low rates. In control rats, 10(-8) M vasopressin added to the bath increased bicarbonate absorption almost threefold. Treatment of rats in vivo with deoxycorticosterone significantly increased the rate of bicarbonate absorption in vitro. In vivo NH4Cl loading also significantly increased bicarbonate absorption. Staining microdissected tubules with acridine orange confirmed that the perfused segments lacked intercalated cells. We conclude that the terminal IMCD spontaneously acidifies the lumen despite an absence of intercalated cells. Bicarbonate absorption appears to be regulated by the same factors that affect net acidification in other collecting duct segments.
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PMID:Net acid transport by isolated perfused inner medullary collecting ducts. 230 97

The alligator excretes a persistently alkaline urine despite consuming an acid-residue diet. The amount of bicarbonate excreted is greater than the amount filtered, evidencing tubular secretion of bicarbonate. The parallel urinary excretion of ammonium maintains external acid balance. To investigate putative renal mechanisms responsible for the concurrent excretion of large quantities of ammonium bicarbonate, we used acridine orange fluorescence methodology in microvesicles prepared from the proximal tubule brush border to assess the activity of the Na+-H+ antiporter, and histochemical methods (cobalt sulfide precipitation) to assess carbonic anhydrase localization. We found no evidence for the presence of a functioning Na+-H+ antiporter, the protein known to be responsible for the majority of bicarbonate reabsorption in mammals; Na+-H+ exchange in vesicles from the alligator kidney failed to exhibit saturation kinetics, showed no affinity for lithium, and was not inhibited by amiloride. Sensitive histochemical techniques failed to reveal carbonic anhydrase activity anywhere in the proximal tubule but detected an abundance of enzyme activity in the basolateral membranes and nuclei of distal tubular cells. In the connecting segment and collecting duct, cells without carbonic anhydrase alternated with cells containing carbonic anhydrase; in the latter, the enzyme was localized to the basolateral and luminal membranes, the nucleus and, to a lesser extent, throughout the cytoplasm. We conclude that the proximal tubule of the alligator kidney is devoid of the machinery necessary for the transport of large amounts of bicarbonate. The principal site at which bicarbonate is added to the final urine appears to be the distal tubule, at which site carbonic anhydrase is widespread.
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PMID:Transport and histochemical studies of bicarbonate handling by the alligator kidney. 253 23

Interference-contrast and fluorescent microscopy were used to differentiate between the two cell types--principal cells (PC) and intercalated cells (IC)--of the isolated perfused cortical collecting duct of the rabbit. Using Hoffman Modulation Contrast optics, two types of cell outlines could be identified: "hexagonal" and "circular" profiles. To characterize the cell types further, the binding of fluorescein-labeled peanut lectin, which has been shown to be specific for the luminal cell membrane of the IC, was monitored with epifluorescent techniques. The lectin was observed to bind to the circular cell type only, confirming it as the IC. With use of the fluorescent nuclear probe acridine orange to quantitate the total number of cells per millimeter of tubule length, the fraction of ICs (lectin-binding cells) was estimated to average 29%, and the fraction of PCs (non-lectin-binding cells) to average 71% of all cells. The studies were extended to functionally separate between the two cell types by monitoring cell swelling when a lumen-to-bath current pulse was passed. Current-induced swelling was observed only in the PC and could be inhibited by the luminal addition of both the Na+ channel blocker amiloride, and the K+ channel blocker barium, thereby implicating the PC in the process of Na+ absorption and K+ secretion in this tissue. It is concluded that optical techniques can be applied to the cortical collecting duct perfused in vitro to differentiate between and study functional properties of the cell types.
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PMID:Functional differentiation of cell types of cortical collecting duct. 257 83

An electrogenic proton-translocating ATPase (H+-ATPase) has been described in turtle urinary bladder and bovine and rat renal medulla. In the present study, a membrane fraction with ATP-dependent H+ transport activity was isolated from human renal medulla. Intravesicular acidification was assessed by acridine orange absorbance changes. Proton transport was abolished by N-ethylmaleimide but not oligomycin or vanadate, differentiating this H+-ATPase from mitochondrial F0-F1 H+-ATPase and gastric H+-K+-ATPase. In addition, vesicular proton uptake was demonstrated to be independent of sodium and potassium cotransport. Proton translocation rate increased when transmembrane potential was clamped with valinomycin supporting an electrogenic mechanism. Hydrogen ion transport was dependent on the presence of chloride or bromide, since substitution by fluoride or nitrate markedly decreased intravesicular acidification. The transport characteristics of this proton-translocating ATPase are similar to those described for turtle urinary bladder and bovine and rat renal medulla, which have been assumed to play a role in urinary acidification by the medullary collecting duct.
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PMID:ATP-dependent proton transport in human renal medulla. 287 44

Intercalated cells play a major role in renal regulation of acid-base balance. We used fluorescent dyes to characterize postnatal maturation of intercalated cells. We stained rabbit collecting ducts with the pH-sensitive dye 6-carboxyfluorescein diacetate and identified individual intercalated cells by their bright green fluorescence. Number of fluorescent cells per millimeter tubule doubled during maturation in midcortex (68 +/- 7 to 121 +/- 9; P less than 0.01) but did not change in outer stripe of outer medulla. Excitation-ratio (490/450 nm) fluorometry of individual cells in nonperfused tubules revealed an increase in pH of cortical intercalated cell from 7.28 +/- 0.03 in newborn to 7.43 +/- 0.03 in adult (P less than 0.005); principal cell pH did not change with age, averaging 7.10 +/- 0.05. The smaller difference in pH between intercalated and principal cells in neonates suggested a paucity of H+ pumps in immature intercalated cells. Indeed, few cortical intercalated cells trapped the weak base acridine orange in cytoplasmic vesicles that contained H+ pumps or demonstrated selective uptake of 3,3'-dipentyloxacarbocyanine, a fluorescent cation that probes for mitochondrial potential. Intercalated cells in neonatal medullary collecting ducts had a cell pH similar to that measured in the adult, as well as numerous acidic cytoplasmic vesicles and significant mitochondrial potentials. In conclusion, intercalated cells in cortical collecting duct underwent postnatal proliferation and maturation, whereas those cells present in outer medullary collecting duct, where proliferation was virtually complete by 1 wk of age, were nearly differentiated. Signals directing this centrifugal pattern of postnatal renal maturation are presently unknown.
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PMID:Postnatal maturation of rabbit renal collecting duct: intercalated cell function. 366 16