Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01185 (vasopressin)
 23,126 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aquaporin water channels are expressed in various fluid-transporting epithelia. Physiological and genetic investigations have revealed that aquaporin channel-like intrinsic protein is expressed in numerous tissues, but its significance in water transport physiology is unclear. It has been shown that aquaporin-collecting duct is a vasopressin-responsive water channel, and that it is regulated by a membrane shuttle mechanism. Three unique models for a water pore have been presented but further studies will be required to verify them. New aquaporin members have been isolated and their discrete localization may reflect their specific physiological roles.
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PMID:Water channels. 856 40

The aquaporins are a family of transmembrane proteins that function as molecular water channels. Recently, a mercurial-insensitive water channel [MIWC or aquaporin-4 (AQP4)] has been cloned, and its mRNA was found to be expressed strongly in kidney inner medulla and several nonrenal tissues. We prepared affinity-purified polyclonal antipeptide antibodies to AQP4 to define the regional distribution and cellular location of this water channel within the kidney. Immunoblotting of membrane fractions from different regions of the kidney revealed strongest expression in the base of the renal inner medulla, with detectable levels also in the inner medullary tip, but little or no expression in the outer medulla or cortex. Immunocytochemistry (light microscopy) revealed renal AQP4 labeling exclusively in the collecting duct principal cells, chiefly in the proximal two-thirds of the inner medullary collecting duct (IMCD). Little or no expression was seen in the outer medullary and cortical collecting ducts. Immunoelectron microscopy demonstrated AQP4 labeling of the basolateral membrane of IMCD cells, with relatively little labeling of intracellular vesicles. Differential centrifugation of inner medullary homogenates also revealed a lack of distribution to the vesicle-enriched fraction, which contains the vasopressin-regulated water channel, aquaporin-2. In contrast to aquaporin-2 and aquaporin-3, water restriction of rats did not increase the level of AQP4 expression. These results suggest a possible role for AQP4 in the basolateral exit of water from the IMCD.
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PMID:Distribution of aquaporin-4 water channel expression within rat kidney. 859 71

We determined whether aquaporin of collecting duct (AQP-CD) is involved in pathogenesis of water retention in rats with experimental models of syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and liver cirrhosis. SIADH rats were made by administering 1-desamino-8-D-arginine vasopressin (DDAVP) subcutaneously and providing them with a liquid diet. Serum Na levels decreased to < 120 meq/l on day 2, and hyponatremia persisted throughout the rest of observation period. Six hours after the DDAVP infusion, the expression of AQP-CD mRNA significantly increased by 198%, followed by > 144% increases in its expression during the 14-day observation period. On day 7, the increased expression of AQP-CD mRNA was abolished after the administration of an antidiuretic, nonpeptide arginine vasopressin (AVP) antagonist, OPC-31260, which was closely related to a marked diuresis and a prompt normalization of serum Na levels in SIADH rats. Rats were made cirrhotic by injecting a mixture of carbon tetrachloride and olive oil subcutaneously for 3 mo. The expression of AQP-CD mRNA was increased by 164% in the decompensated cirrhotic rats. The blockade of AVP action by OPC-31260 significantly diminished its expression. These results indicate that water channel AQP-CD plays an important role in water retention in pathological states of SIADH and liver cirrhosis.
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PMID:Role of water channel AQP-CD in water retention in SIADH and cirrhotic rats. 859 89

Prolonged hypokalemia causes vasopressin-resistant polyuria. We have recently shown that another cause of severe polyuria, chronic lithium therapy, is associated with decreased aquaporin-2 (AQP2) water channel expression (Marples, D., S. Christensen, E.I. Christensen, P.D. Ottosen, and S. Nielsen, 1995. J. Clin. Invest., 95: 1838-1845). Consequently, we studied the effect in rats of 11 days' potassium deprivation on urine production and AQP2 expression and distribution. Membrane fractions were prepared from one kidney, while the contralateral kidney was perfusion-fixed for immunocytochemistry. Immunoblotting and densitometry revealed a decrease in AQP2 levels to 27+/-3.4% of control levels (n=11, P<0.001) in inner medulla, and 34+/-15% of controls (n=5, P<0.05) in cortex. Urine production increased in parallel, from 11+/-1.4 to 30+/-4.4 ml/day (n=11, P<0.01). After return to a potassium-containing diet both urine output and AQP2 labels normalized within 7 d. Immunocytochemistry confirmed decreased AQP2 labeling in principal cells of both inner medullary and cortical collecting ducts. AQP2 labeling was predominantly associated with the apical plasma membrane and intracellular vesicles. Lithium treatment for 24 d caused a more extensive reduction of AQP2 levels, to 4+/-1% of control levels in the inner medulla and 4+/-2% in cortex, in association with severe polyuria. The similar degree of downregulation in medulla and cortex suggests that interstitial tonicity is not the major factor in the regulation of AQP2 expression. Consistent with this furosemide treatment did not alter AQP2 levels. In summary,hypokalemia, like lithium treatment, results in a decrease in AQP2 expression in rat collecting ducts, in parallel with the development of polyuria, and the degree of downregulation is consistent with the level of polyuria induced, supporting the view that there is a causative link.
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PMID:Hypokalemia-induced downregulation of aquaporin-2 water channel expression in rat kidney medulla and cortex. 862 81

The renal urea transporter (RUT) is responsible for urea accumulation in the renal medulla, and consequently plays a central role in the urinary concentrating mechanism. To study its cellular and subcellular localization, we prepared affinity-purified, peptide-derived polyclonal antibodies against rat RUT based on the cloned cDNA sequence. Immunoblots using membrane fractions from rat renal inner medulla revealed a solitary 97-kDa band. Immunocytochemistry demonstrated RUT labeling of the apical and subapical regions of inner medullary collecting duct (IMCD) cells, with no labeling of outer medullary or cortical collecting ducts. Immunoelectron microscopy directly demonstrated labeling of the apical plasma membrane and of subapical intracellular vesicles of IMCD cells, but no labeling of the basolateral plasma membrane. Immunoblots demonstrated RUT labeling in both plasma membrane and intracellular vesicle-enriched membrane fractions from inner medulla, a subcellular distribution similar to that of the vasopressin-regulated water channel, aquaporin-2. In the outer medulla, RUT labeling was seen in terminal portions of short-loop descending thin limbs. Aside from IMCD and descending thin limbs, no other structures were labeled in the kidney. These results suggest that: (i) the RUT provides the apical pathway for rapid, vasopressin-regulated urea transport in the IMCD, (ii) collecting duct urea transport may be increased by vasopressin by stimulation of trafficking of RUT-containing vesicles to the apical plasma membrane, and (iii) the rat urea transporter may provide a pathway for urea entry into the descending limbs of short-loop nephrons.
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PMID:Cellular and subcellular localization of the vasopressin- regulated urea transporter in rat kidney. 864 3

The arcades are long, branched renal tubules which connect deep and mid-cortical nephrons to cortical collecting ducts in the renal cortex. Because they are inaccessible by standard physiological techniques, their functions are poorly understood. In this paper, we demonstrate that the arcades are a site of expression of two proteins, aquaporin-2 (the vasopressin-regulated water channel) and the V2 vasopressin receptor, that are important to regulated water transport in the kidney. Using a peptide-derived polyclonal antibody to aquaporin-2, quantitative ELISA in microdissected segments showed that aquaporin-2 is highly expressed in arcades and that the expression is increased in response to restriction of fluid intake. Immunocytochemistry revealed abundant aquaporin-2 labeling of structures in the cortical labyrinth in a pattern similar to that of the Na(+)-Ca2+ exchanger and kallikrein, marker proteins expressed in arcades but not in cortical collecting ducts. RT-PCR experiments demonstrated substantial aquaporin-2 and V2 receptor mRNA in microdissected arcades. In situ hybridization, using 35S-labeled antisense cRNA probes for the V2 receptor demonstrated strong labeling of both arcades and cortical collecting ducts. Thus, these results indicate that the arcades contain the specific proteins associated with vasopressin-regulated water transport, and may be a heretofore unrecognized site of free water absorption.
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PMID:Rat renal arcade segment expresses vasopressin-regulated water channel and vasopressin V2 receptor. 867 87

To evaluate the possible role of a putative vesicle-targeting protein, syntaxin-4, in vasopressin-regulated trafficking of aquaporin-2 water channel vesicles to the apical plasma membrane of renal collecting duct cells, we have carried out immunoblotting, immunocytochemistry, and reverse transcription (RT)-PCR experiments in rat kidney. Immunochemical studies used an affinity-purified, peptide-directed polyclonal antibody to rat syntaxin-4. Immunoblots using membrane fractions from inner medullary collecting duct (IMCD) cell suspensions revealed a solitary protein of 36 kD, the expected molecular mass of syntaxin-4. This protein was enriched in a plasma membrane-enriched membrane fraction from IMCD cells. Immunoperoxidase immunocytochemistry in 0.85-microm cryosections from rat inner medulla revealed discrete labeling of the apical plasma membrane of IMCD cells. RT-PCR demonstrated the presence of syntaxin-4 mRNA in microdissected IMCD segments, confirmed by direct sequencing of the PCR product. In addition, RT-PCR experiments demonstrated syntaxin-4 mRNA in glomeruli, vasa recta, connecting tubules, and thin descending limbs of Henle's loops. The demonstrated localization of syntaxin-4 in the apical plasma membrane of collecting duct principal cells, coupled with previous demonstration of syntaxin-4's putative cognate receptor VAMP2 in aquaporin-2-containing vesicles, supports the view that these proteins could play a role of aquaporin-2 vesicle targeting to the apical plasma membrane.
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PMID:Syntaxin-4 is localized to the apical plasma membrane of rat renal collecting duct cells: possible role in aquaporin-2 trafficking. 877 Aug 61

Vasopressin-dependent membrane insertion of aquaporin-2 (AQP-2) in collecting duct principal cells has been demonstrated in vivo and in vitro. However, the hypothesis that the AQP-2 molecule recycles between intracellular vesicles and the plasma membrane in response to hormonal stimulation and withdrawal remains to be demonstrated directly. In the present study, we examined AQP-2 recycling between intracellular vesicles and the plasma membrane in the absence of de novo protein synthesis using LLC-PK1 cells transfected with an AQP-2-c-myc construct. Cells were treated with cycloheximide for 30 min prior to vasopressin stimulation, and all subsequent treatments were performed in the continued presence of cycloheximide. Complete inhibition of AQP-2 biosynthesis by cycloheximide was verified by immuno-precipitation. Immunofluorescence revealed that AQP-2 was located on intracellular vesicles in nonstimulated cells but was relocated to the plasma membrane after vasopressin treatment, even in the presence of cycloheximide. After vasopressin washout, AQP-2 was retrieved to intracellular vesicles and was relocated to the plasma membrane after restimulation with forskolin. Subsequent forskolin washout resulted in AQP-2 endocytosis, and a second stimulation with forskolin resulted in relocation to the plasma membrane. These data, obtained in the absence of de novo protein synthesis, clearly indicate that AQP-2 can be recycled multiple times between intracellular vesicles and the plasma membrane.
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PMID:Direct demonstration of aquaporin-2 water channel recycling in stably transfected LLC-PK1 epithelial cells. 878 Feb 59

Hereditary nephrogenic diabetes insipidus (NDI) is caused by mutations in either the X-chromosomal gene encoding the vasopressin V2-receptor or in the autosomal gene encoding aquaporin-2. Expressed in Xenopus oocytes, the AQP2 gene mutations found in NDl have been shown to reduce the stability of the encoded protein. This study investigated the in vivo stability of mutant and wild-type aquaporin-2 proteins by measuring their excretion in urine of NDl patients and healthy individuals. On immunoblots, the urine samples from healthy volunteers revealed clear aquaporin-1 and aquaporin-2 signals in antidiuretic but not diuretic states. In the urine of a female patient, whose NDl is explained by low expression of the wild-type V2-receptor gene, aquaporin-2 excretion was high and comparable with that in a healthy individual during antidiuresis. In the urine of a male patient with a non-sense mutation in the V2-receptor gene, a weak aquaporin-2 signal was detected. In NDl patients with mutations in the aquaporin-2 gene, aquaporin-2 could not be detected in urine, suggesting a low stability of mutant aquaporin-2 proteins. In four out of seven NDl patients, aquaporin-1 excretion was relatively high, which suggests a compensatory increase in proximal reabsorption in NDl.
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PMID:Urinary content of aquaporin 1 and 2 in nephrogenic diabetes insipidus. 879 91

Discovery of aquaporin water channel proteins has provided insight into the molecular mechanism of membrane water permeability. The distribution of known mammalian aquaporins predicts roles in physiology and disease. Aquaporin-1 mediates proximal tubule fluid reabsorption, secretion of aqueous humor and cerebrospinal fluid, and lung water homeostasis. Aquaporin-2 mediates vasopressin-dependent renal collecting duct water permeability; mutations or downregulation can cause nephrogenic diabetes insipidus. Aquaporin-3 in the basolateral membrane of the collecting duct provides an exit pathway for reabsorbed water. Aquaporin-4 is abundant in brain and probably participates in reabsorption of cerebrospinal fluid, osmoregulation, and regulation of brain edema. Aquaporin-5 mediates fluid secretion in salivary and lacrimal glands and is abundant in alveolar epithelium of the lung. Specific regulation of membrane water permeability will likely prove important to understanding edema formation and fluid balance in both normal physiology and disease.
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PMID:Pathophysiology of the aquaporin water channels. 881 12


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