Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The stimulation of alpha-1 adrenergic receptors in the mammalian nephron increases sodium reabsorption. In this study, alpha-1 adrenergic receptors in the inner medullary collecting duct (IMCD) cells were examined by radioligand binding technique. The IMCD cells were prepared from the rabbit kidney by incubating the inner medullary slices with collagenase and treating the isolated cells with hypotonic solution to lyse cells other than IMCD cells. The equilibrium binding of [3H]prazosin to IMCD cell homogenate was measured after incubation for 30 min at 25 degrees C in the absence (total binding) and the presence (nonspecific binding) of 100 microM phentolamine. The specific binding (the difference between total and nonspecific binding) of [3H]prazosin was saturable with a Bmax of 30 fmol/mg of protein and Kd of 0.9 nM. The displacement of [3H]prazosin binding to IMCD cells by adrenergic antagonists and agonists displayed the order of potency: beta-4-hydroxyphenyl-ethyl-amino-tetralone greater than phentolamine greater than naphazoline greater than epinephrine greater than yohimbine greater than norepinephrine greater than phenylephrine greater than propranolol. Because IMCD cells in the kidney have a hypertonic environment, the specific binding of [3H] prazosin to IMCD cells was also measured in a buffer that was made hypertonic (1200 mOsmol/kg of water) with NaCl and urea, the major solutes of the renal medulla. The hyperosmolality increased the Kd of [3H]prazosin to 5.2 mM without a change in its Bmax.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Alpha-1 adrenergic receptors in renal medullary collecting duct cells. 168 13

Fine control of renal water and electrolyte excretion takes place in the collecting duct, a tubule segment which is also a major site of K+ secretion and hormone action. With the introduction of patch clamp techniques it has been possible to define the contribution of ion channels to K+ transport. Two types of channels have been identified in the cortical collecting tubules of the rabbit and rat: (1) a maxi- or high conductance K+ channel (single channel conductance greater than 80 pS) found only in the apical membrane, and (2) smaller conductance K+ channels (single channel conductance less than 60 pS) found in both apical and basolateral membranes. The gating properties of the K+ channels with smaller conductances differ in the apical and basolateral cell membranes; whereas the open probability of the small conductance K+ channel in the apical membrane is not voltage-sensitive, that of the basolateral channel increases with hyperpolarization. The maxi-K+ channel, so far only found in the apical cell membrane, is voltage-gated but its open probability increases with cell depolarization. The possible role of these K+ channels in different states of the K+ transport system in collecting ducts is discussed.
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PMID:K+ channels of the mammalian collecting duct. 168 62

The water permeability of the kidney collecting duct epithelium is regulated by vasopressin (VP)-induced recycling of water channels between an intracellular vesicular compartment and the plasma membrane of principal cells. To test whether the water channels pass through an acidic endosomal compartment during the endocytic portion of this pathway, we measured ATP-dependent acidification of FITC-dextran-labeled endosomes in isolated microsomal fractions from different regions of Brattleboro rat kidneys. Both VP-deficient controls and rat treated with exogenous VP were examined. ATP-dependent acidification was not detectable in endosomes containing water channels from distal papilla (osmotic water permeability Pf = 0.038 +/- 0.004 cm/s). In contrast, the addition of ATP resulted in a strong acidification of renal cortical endosomes (pHmin = 5.8, initial rate = 0.18-0.25 pH U/s). Acidification of cortical endosomes was reversed with nigericin and strongly inhibited by N-ethyl-maleimide. Passive proton permeability was similar and low in both cortical and papillary endosomes from rats treated or not treated with VP. The fraction of labeled endosomes present in microsomal preparations was determined by fluorescence imaging microscopy of microsomes nonspecifically bound to poly-l-lysine-coated coverslips and was 25% in cortical preparations compared to 14% (+VP) and 9% (-VP) in papillary preparations. The fraction of cortical endosomes was enriched 1.5-fold by immunoabsorption to coverslips coated with mAbs against the bovine vacuolar proton pump. In contrast, the fraction of papillary endosomes was depleted more than twofold by immunoabsorption to identical coverslips. Finally, sections of distal papilla stained with antibodies against the lysosomal glycoprotein LGP120 showed that most of the entrapped FITC-dextran did not colocalize with this lysosomal protein. These results demonstrate that vesicles which internalize water channels in kidney collecting duct principal cells lack functional proton pumps, and do not deliver the bulk of their FITC-dextran content to lysosomes. The data suggest that the principal cell contains a specialized nonacidic apical endocytic compartment which functions primarily to recycle membrane components, including water channels, to the plasma membrane.
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PMID:Endocytic vesicles from renal papilla which retrieve the vasopressin-sensitive water channel do not contain a functional H+ ATPase. 169 62

Antidiuretic hormone (ADH) stimulation of toad urinary bladder granular cells causes simultaneous increases in transepithelial water and H+ permeabilities (PF and PH+, respectively), suggesting that ADH-elicited water channels inserted into granular cell apical membranes might be permeable to both water and H+. We have previously used self-quenching fluorophores entrapped within endocytic vesicles selectively retrieved from water-permeable apical membranes to measure vesicle PF. The membranes of these vesicles possess an extremely high PF such that our measurements provide only minimum estimates of vesicle PF and have limited our ability to quantitate the properties of ADH water channels. We therefore quantitated vesicle PH+ using similar rapid mixing techniques. Vesicle PH+ was 5.1 +/- 0.5 x 10(-3) cm/s. Activation energy of this process was 3.6 +/- 0.6 kcal/mol, indicative of H+ flux through an aqueous channel. The mercurial reagent, para-chloromercuribenzenesulfonate (PCMBS), which inhibits ADH-stimulated transepithelial PF in intact bladders by 50-60%, inhibited vesicle PH+ by 55%. N-Ethylmaleimide and phloretin, which do not alter ADH-stimulated PF, did not affect vesicle PH+. We conclude that membranes containing ADH water channels possess substantial PH+ that likely reflects proton flux through water channels. The apparent high PH+ of the ADH water channel may have important implications for intracellular trafficking of these water channels in ADH-responsive epithelial cells.
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PMID:High proton flux through membranes containing antidiuretic hormone water channels. 169 88

Vasopressin action in the renal collecting duct is believed to be mediated by the cycling of water channels in principal and, possibly, intercalated cells. We used 6-carboxyfluorescein (6-CF) or fluorescein-labeled dextran (FITC-dextran) to determine the location and water permeability of endocytic vesicles from papilla and inner stripe of Brattleboro rats in different states of diuresis. Fifteen minutes after FITC-dextran infusion, fluorescent vesicles were concentrated at the apical pole of principal and intercalated cells. The osmotic water permeability (Pf) of these endosomes was measured by fluorescence quenching. In papillary endosomes, Pf was high (0.04 +/- 0.004 cm/s) when rats were in physiological states of antidiuresis or after treatment with vasopressin, 1-desamino-8-D-arginine vasopressin (DDAVP), or oxytocin; endosomes isolated from these regions of untreated animals had a low Pf. The number of papillary endosomes with high Pf increased with increasing doses of DDAVP. Endosomes from the inner stripe also had a high Pf only after vasopressin treatment. Confocal microscopy of sections of papilla showed that vasopressin significantly increased endocytosis in principal cells but had no effect on intercalated cells. Our data demonstrate that the bulk of fluorescently labeled vesicles from the papilla originate from the apical membrane of principal cells and contain water channels in their limiting membrane only when the rats are in physiological states of antidiuresis. In contrast, the majority of endocytosis in intercalated cells is not involved in water channel recycling.
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PMID:Endocytosis of water channels in rat kidney: cell specificity and correlation with in vivo antidiuresis. 170 69

ICI 207,828 is a novel eukalemic diuretic in animals that is comparable in effect to hydrochlorothiazide. We used micropuncture and microperfusion techniques to determine the site(s) of action of this compound in the rat nephron. Either furosemide (FUR) or ICI 207,828 were perfused through the loop of Henle in situ. Both compounds caused significant reduction in water and electrolyte reabsorption by the loop. The effect of ICI 207,828 was significantly less than that of FUR. Both amiloride and ICI 207,828 were perfused, in situ, through the superficial distal tubule. ICI 207,828 had an effect similar to amiloride. Sodium and water reabsorption and potassium secretion were inhibited. In free-flow micropuncture studies, ICI 207,828, infused continuously i.v., had little effect on electrolyte and water reabsorption by the superficial proximal tubule. This compound significantly inhibited water and electrolyte reabsorption by the loop of Henle. Distal tubule secretion of potassium was inhibited. In addition, fractional potassium reabsorption beyond the superficial, late distal tubule was inhibited by ICI 207,828. From these results, we conclude that ICI 207,828 significantly inhibits electrolyte and water transport by the loop of Henle and distal tubule, and at sites beyond the superficial distal tubule such as either the collecting duct system or juxtamedullary nephrons. The reduction in distal potassium secretion, in concert with reduced loop of Henle and postdistal reabsorption, results in no net potassium loss in the urine, thus rendering this compound eukalemic.
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PMID:Evaluation of the renal site of action of a novel, eukalemic diuretic, ICI 207,828. 173 95

Antidiuretic hormone (ADH) stimulation of toad bladder granular cells rapidly increases the osmotic water permeability (Pf) of their apical membranes by insertion of highly selective water channels. Before ADH stimulation, these water channels are stored in large cytoplasmic vesicles called aggrephores. ADH causes aggrephores to fuse with the apical membrane. Termination of ADH stimulation results in prompt endocytosis of water channel-containing membranes via retrieval of these specialized regions of apical membrane. Protein components of the ADH water channel contained within these retrieved vesicles would be expected to be integral membrane protein(s) that span the vesicle's lipid bilayer to create narrow aqueous channels. Our previous work has identified proteins of 55 (actually a 55/53-kDa doublet), 17, 15, and 7 kDa as candidate ADH water channel components. We now have investigated these candidate ADH water channel proteins in purified retrieved vesicles. These vesicles do not contain a functional proton pump as assayed by Western blots of purified vesicle protein probed with anti-H(+)-ATPase antisera. Approximately 60% of vesicle protein is accounted for by three protein bands of 55, 53, and 46 kDa. Smaller contributions to vesicle protein are made by the 17- and 15-kDa proteins. Triton X-114-partitioning analysis shows that the 55, 53, 46, and 17 kDa are integral membrane proteins. Vectorial labeling analysis with two membrane-impermeant reagents shows that the 55-, 53-, and 46-kDa protein species span the lipid bilayer of these vesicles. Thus the 55-, 53-, and 46-kDa proteins possess characteristics expected for ADH water channel components. These data show that the 55- and 53- and perhaps the 46-, 17-, and 15-kDa proteins are likely components of aqueous transmembrane pores that constitute ADH water channels contained within these vesicles.
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PMID:Quantitation and topography of membrane proteins in highly water-permeable vesicles from ADH-stimulated toad bladder. 183 Apr 55

Endothelins regulate nephron sodium and water transport, prostaglandin E2 (PGE2) synthesis, and phospholipid metabolism. Recent studies suggest that renal tubule cells synthesize endothelins. To determine which nephron sites have such potential, endothelin production by cells derived from different nephron segments was examined. Immunoreactive endothelin 1 (ET-1) and endothelin 3 (ET-3) were measured in supernatants of cultured rabbit proximal tubule (PT), medullary thick ascending limb (MTAL), cortical collecting tubule (CCT), and inner medullary collecting duct (IMCD) cells. All cell types released immunoreactive ET-1 and ET-3. However, the amounts of endothelin produced differed as follows: IMCD greater than MTAL greater than CCT much greater than PT for ET-1 and IMCD greater than MTAL = PT = CCT for ET-3; in all cases ET-1 much greater than ET-3. To confirm de novo ET-3 synthesis, IMCD cells were labeled with [35S]cysteine, and the supernatant was immunoprecipitated with anti-ET-3 antibody. Sample and standard ET-3 eluted at identical positions on high-performance liquid chromatographs, confirming de novo synthesis of ET-3 by cultured IMCD cells. These data raise the possibility of an important functional role for nephron-derived endothelin and, in particular, endothelin produced by tubule cells in the medulla.
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PMID:Endothelin synthesis by rabbit renal tubule cells. 187 47

We have shown that urea transport across the terminal inner medullary collecting duct (terminal IMCD) is mediated by a vasopressin-stimulated, facilitated diffusion process exhibiting properties consistent with a transporter. To investigate whether hypertonic NaCl, as exists in vivo in the inner medulla, affects urea permeability, we studied isolated perfused rat terminal IMCD segments. Perfusate and bath osmolality were varied symmetrically by adding or removing NaCl or mannitol. Urea permeability rose progressively when osmolality was increased with NaCl or mannitol from 290 to 690 mOsm/kg H2O in the absence of vasopressin; there was no further increase at 890 mOsm/kg H2O. In the presence of 10(-8) M arginine vasopressin, urea permeability increased when NaCl was added to raise osmolality from 290 to 490 mOsm/kg H2O but there was no further increase at 690 mOsm/kg H2O. When 1 mM 8-bromo cyclic AMP was added to the bath, raising NaCl still increased urea permeability. These results suggest that urea transport across the rat terminal IMCD is regulated both by vasopressin and by osmolality at values present in the renal inner medulla. Osmolality seems to activate urea transport across the rat terminal IMCD by mechanisms distinct from those of vasopressin or cyclic AMP.
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PMID:An independent effect of osmolality on urea transport in rat terminal inner medullary collecting ducts. 190 26

We examined the action of high (2 x 10(-8)M) and low (6 x 10(-9)M) concentrations of atrial natriuretic factor (ANF) on water and urea transport in the rat inner medullary collecting duct (IMCD) using the in vitro microperfusion technique. We measured the hydraulic conductivity (Lp x 10(-6) cm/atm per second) and both lumen-to-bath (Pu(lb] and bath-to-lumen (Pu(bl)) 14C-urea permeabilities (Pu x 10(-5) cm/s) in the absence and in the presence of vasopressin (VP). High concentrations of ANF were able to inhibit the maximum activity of (50 microU/ml) VP-stimulated Lp but physiological concentration of ANF inhibit only submaximum activity (10 microU/ml) of VP-stimulated Lp. The hydrosomotic effect of dibutyryl-cyclic 3.5 adenosine monophosphate (cAMP) (10(-4)M) was unchanged by high concentrations of ANF (2 x 10(-8)M). Also we found that high (10(-4)M) and low (10(-6)M) concentrations of exogenous cyclic 3,5-guanosine monophosphate (GMP) while unable to change the Lp in the absence of VP, decreased the maximum activity of VP-stimulated Lp significantly. We also found that ANF inhibits partially and in a reversible manner the VP-stimulated Pu(lg) but not the VP-stimulated Pu(bl). These results demonstrated that plasma concentrations of ANF observed during volume expansion (10(-10)M) are able to inhibit submaximum activity of VP-stimulated (10 microU/ml) Lp in the rat IMCD, this effect seems to occur before cAMP formation and it appears to be mediated by cGMP. ANF (6 x 10(-9)M) also reduced the VP-stimulated urea outflux.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of atrial natriuretic factor and cyclic guanosine monophosphate on water and urea transport in the inner medullary collecting duct. 196 94


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