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Biomedical subjects

S Nielsen

Publications and source records attributed to S Nielsen.

At least 235 records · Page 13Linked to original sources
PubMed1995

Incidence of eating disorders in psychiatric hospitals and wards in Denmark, 1970-1993.

Two previous studies in Denmark found diverging results in analyzing trends in new cases of eating disorders in the psychiatric in- and day-patient services, although the same data source, the nationwide Danish Psychiatric Case Register, was used. The present study--also using information from the nationwide Danish Psychiatric Case Register, but correcting for several register biases--confirms a highly significant increase in new cases of eating disorders in psychiatric hospitals and wards. The increase is seen exclusively in younger females. The diverging results in the previously mentioned studies in Denmark may be ascribed to methodological issues.

Adolescent↗
PubMed1995

Redistribution of aquaporin-2 water channels induced by vasopressin in rat kidney inner medullary collecting duct.

Aquaporin-2 (AQP2) is the predominant vasopressin-regulated water channel of the renal collecting duct. We tested whether vasopressin induces translocation of AQP2 from intracellular vesicles into the apical plasma membrane. AQP2 was quantitated in plasma membrane and intracellular vesicle fractions prepared from the inner medulla of one kidney from each rat before or 20 min after intravenous 1-desamino-8-D-arginine vasopressin (DDAVP) treatment, using immunoblotting and densitometry. Contralateral kidneys were prepared for immunofluorescence and immunoelectron microscopy. Immunoblotting revealed that, compared with untreated controls, DDAVP treatment significantly increased the fraction of AQP2 protein associated with the plasma membrane fraction relative to intracellular vesicles. This increase averaged 2.0-fold in untreated rats and 2.9-fold in rats water loaded for 12 h. Water loading, presumably by suppressing circulating vasopressin levels, decreased the fraction of AQP2 associated with the plasma membrane by 55%, suggesting retrieval of AQP2 from the plasma membrane. In rats sequentially thirsted for 48 h to increase expression and then water loaded for 72 h to minimize plasma membrane labeling, DDAVP caused a 12-fold increase in the plasma membrane to intracellular vesicle labeling ratio. The accentuation of the DDAVP response seen after water loading is consistent with the observed increase in the fraction of AQP2 in the intracellular pool available for insertion. Immunofluorescence confirmed a marked DDAVP-induced redistribution of AQP2 from intracellular to plasma membrane domains. Furthermore, quantitative immunoelectron microscopy demonstrated a 3.4-fold increase in apical plasma membrane to intracellular vesicle labeling ratio. These results provide a direct in vivo demonstration of vasopressin-induced translocation of AQP2 into the apical plasma membrane.

Animals↗
PubMed1995

Aquaporin-1 water channels in short and long loop descending thin limbs and in descending vasa recta in rat kidney.

The localization of aquaporin-1 water channels (AQP-1) in nephron and vascular structures in rat kidney were characterized, because vascular bundles are known to play a key role in urinary concentration. Immunohistochemistry and immunoelectron microscopy were applied on thin cryosections or ultrathin Lowicryl sections, using an optimized freeze-substitution method. Within the vascular bundles, AQP-1 is localized in descending thin limbs (DTL) of short nephrons in apical and basolateral membranes. The expression in DTL of short nephrons is considerably lower compared with the expression in long nephrons, consistent with the known lower osmotic water permeability of this segment. Furthermore, DTL of short nephrons expressing AQP-1 continue abruptly into a thin limb segment without AQP-1. This suggests the existence of a novel thin limb epithelium in the outer medulla. Extensive expression of AQP-1 is observed in apical and basolateral membranes of DTL of long nephrons, which are localized in the periphery of the vascular bundles. The expression decreases along the axis of long nephron DTLs in correlation with the known water permeability characteristics of thin limb segments. DTLs of both short and long nephrons continue abruptly into thin limb segments without AQP-1 expression, revealing an abrupt cell-to-cell transition. In vasa recta, AQP-1 is selectively localized in the nonfenestrated endothelium of descending vasa recta, whereas the fenestrated endothelium of ascending vesa recta and peritubular capillaries do not express AQP-1. AQP-1 is localized in both apical and basolateral plasma membranes, which is logical for transendothelial water transport. Isolated perfused descending vasa recta display high water permeability, and, unlike sodium permeability, diffusional water permeability is partly inhibited by mercurials, thus substantiating the presence of mercurial-sensitive water channels in descending vasa recta. Thus AQP-1 is localized in DTL and descending vasa recta within vascular bundles, and AQP-1 expression in DTL segments is in exact concordance with the known water permeability characteristics, strongly supporting that AQP-1 is the major constitutive water channel of the nephron.

Animals↗
PubMed1995

Diffusive transport of solute in the rat medullary microcirculation.

Outer medullary descending vasa recta (OMDVR) permeability to sodium (PNa) is much lower than to urea (Purea). Based on these findings, we hypothesized that sodium and urea diffuse across the OMDFR wall by separate routes. To further test this, we simultaneously perfused OMDVR with 22Na and 36Cl, [14C]urea, [3H]raffinose, or tritiated water. The permeability of OMDVR to 22Na and [3H]raffinose was found to increase markedly and reversibly with perfusion rate. PNa was highly correlated with the permeability to Cl (PCl) and to [3H]raffinose (Praf) (R = 0.90 and 0.95, respectively) but not with Purea (R = 0.23). Praf was also correlated with inulin permeability (PIn) (R = 0.93). The intercepts for the regressions of PNa with PCl and Praf and for Praf with PIn were zero. In contrast, OMDVR with low PNa retained very high diffusional water permeability (PD) and Purea, a finding consistent with separate routes for permeation of those tracers. We previously established that thiourea is a competitive inhibitor of OMDVR urea transport. In the presence of 100 mM thiourea, OMDVR PNa and Purea were correlated (R = 0.71) but retained an intercept much > 0. We conclude that Na, Cl, raffinose, and inulin are likely to traverse the OMDVR wall through a common pathway, whereas specific mechanisms exist to regulate the permeation by urea and water.

Animals↗
PubMed1995

Oxytocin as an antidiuretic hormone. I. Concentration dependence of action.

Circulating concentrations of oxytocin increase to 10-40 pM in rats in response to osmotic stimuli, suggesting that oxytocin could play a role in regulation of water balance. The present studies tested whether oxytocin at such concentrations increases osmotic water permeability (Pf) in isolated perfused terminal inner medullary collecting ducts (IMCD). In IMCD segments from Sprague-Dawley rats, 20 pM oxytocin added to the peritubular bath caused a two- to threefold increase in Pf, whereas 200 pM oxytocin increased Pf by five- to sixfold (n = 8, P < 0.01). IMCD from Brattleboro rats, which manifest central diabetes insipidus, exhibited a 2.8-fold increase in Pf in response to 20 pM oxytocin and a 4.7-fold increase in response to 200 pM oxytocin. However, in Brattleboro rats, the response to 20 pM oxytocin was dependent on prior water restriction of the rats. Immunoblotting showed no change in the expression of the aquaporin-CD water channel in Brattleboro rats in response to water restriction. Nevertheless, immunofluorescence studies of inner medullary tissue from Brattleboro rats revealed a marked redistribution of the aquaporin-CD water channels to a predominantly apical and subapical localization in IMCD cells in response to water restriction, similar to the redistribution seen in response to vasopressin. Mathematical modeling studies revealed that the measured increase in Pf in response to oxytocin is sufficient to generate a concentrated urine. We conclude that oxytocin can function physiologically as an antidiuretic hormone, mimicking the short-term action of vasopressin on water permeability, albeit with somewhat lower potency.

Animals↗
PubMed1995

Aquaporin-3 water channel localization and regulation in rat kidney.

The aquaporins are a family of water channels expressed in several water-transporting tissues, including the kidney. We have used a peptide-derived, affinity-purified polyclonal antibody to aquaporin-3 (AQP-3) to investigate its localization and regulation in the kidney. Immunoblotting experiments showed expression in both renal cortex and medulla, with greatest expression in the base of the inner medulla. Subcellular fractionation of membranes, using progressively higher centrifugation speeds, revealed that AQP-3 is present predominantly in the 4,000 and 17,000 g pellets and, in contrast to AQP-2, is virtually absent in the high-speed (200,000 g) pellet that contains small intracellular vesicles. Immunocytochemistry and immunofluorescence studies revealed that labeling is restricted to the cortical, outer medullary, and inner medullary collecting ducts. Within the collecting duct, principal cells were labeled, whereas intercalated cells were unlabeled. Consistent with previous immunofluorescence studies (K. Ishibashi, S. Sasaki, K. Fushimi, S. Uchida, M. Kuwahara, H. Saito, T. Furukawa, K. Nakajima, Y. Yamaguchi, T. Gojobori, and F. Marumo. Proc. Natl. Acad. Sci. USA 91: 6269-6273, 1994; T. Ma, A. Frigeri, H. Hasegawa, and A. S. Verkman. J. Biol. Chem. 269: 21845-21849, 1994), the labeling was confined to the basolateral domain. Immunoelectron microscopy, using the immunogold technique in ultrathin cryosections, demonstrated a predominant labeling of the basolateral plasma membranes. In contrast to previous findings with AQP-2, there was only limited AQP-3 labeling of intracellular vesicles, suggesting that this water channel is not regulated acutely through vesicular trafficking. Immunoblotting studies revealed that thirsting of rats for 48 h approximately doubled the amount of AQP-3 protein in the inner medulla. These studies are consistent with a role for AQP-3 in osmotically driven water absorption across the collecting duct epithelium and suggest that the expression of AQP-3 is regulated on a long-term basis.

Amino Acid Sequence↗
PubMed1995

Distribution of aquaporin-4 water channel expression within rat kidney.

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.

Amino Acid Sequence↗
PubMed1995

Lithium-induced downregulation of aquaporin-2 water channel expression in rat kidney medulla.

Lithium, a widely used treatment for bipolar affective disorders, often causes nephrogenic diabetes insipidus. The effect of chronic lithium therapy on the expression of the vasopressin-regulated water channel Aquaporin-2 (AQP2) in rat kidney was examined. Membranes were prepared from inner medulla of one kidney from each rat, while the contralateral one was fixed for immunofluorescence and immunoelectronmicroscopy. Immunoblotting revealed that lithium treatment reduced AQP2 expression dramatically, to 31 +/- 8% after 10 d and to 4 +/- 1% after 25 d, coincident with development of severe polyuria. Immunofluorescence and immunogold quantitation confirmed the lithium-induced decrease in AQP2 expression (from 11.2 +/- 1.0 to 1.1 +/- 0.2 particles/microns 2). The downregulation was only partly reversed by return to lithium-free diet for 1 wk (40 +/- 8% of control). Furthermore, immunoblotting and immunogold quantitation revealed that 2 d of thirsting or 7 d of dDAVP treatment, in the continued presence of lithium, increased AQP2 expression by six- and threefold, respectively, coincident with increased urinary osmolality. Thirsting increased AQP2 immunolabeling mainly of vesicles, whereas dDAVP caused accumulation of AQP2 predominantly in the subapical region and plasma membrane. Thus, lithium causes marked downregulation of AQP2 expression, only partially reversed by cessation of therapy, thirsting or dDAVP treatment, consistent with clinical observations of slow recovery from lithium-induced urinary concentrating defects.

Animals↗
PubMed1995

Expression of VAMP-2-like protein in kidney collecting duct intracellular vesicles. Colocalization with Aquaporin-2 water channels.

Body water balance is controlled by vasopressin, which regulates Aquaporin-2 (AQP2) water channels in kidney collecting duct cells by vesicular trafficking between intracellular vesicles and the plasma membrane. To examine the molecular apparatus involved in vesicle trafficking and vasopressin regulation of AQP2 in collecting duct cells, we tested if targeting proteins expressed in the synaptic vesicles, namely vesicle-associated membrane proteins 1 and 2 (VAMP1 and 2), are expressed in kidney collecting duct. Immunoblotting revealed specific labeling of VAMP2 (18-kD band) but not VAMP1 in membrane fractions prepared from kidney inner medulla. Controls using preadsorbed antibody or preimmune serum were negative. Bands of identical molecular size were detected in immunoblots of brain membrane vesicles and purified synaptic vesicles. VAMP2 in kidney membranes was cleaved by tetanus toxin, revealing a tetanus toxin-sensitive VAMP homologue. Similarly, tetanus toxin cleaved VAMP2 in synaptic vesicles. In kidney inner medulla, VAMP2 was predominantly expressed in the membrane fraction enriched for intracellular vesicles, with little or no VAMP2 in the plasma membrane enriched fraction. This was confirmed by immunocytochemistry using semithin cryosections, which showed mainly vesicular labeling in collecting duct principal cells, with no labeling of intercalated cells. VAMP2 immunolabeling colocalized with AQP2 labeling in intracellular vesicles, as determined by immunoelectron microscopy after double immunolabeling of isolated vesicles. Quantitative analysis of 1,310 vesicles revealed a highly significant association of both AQP2 and VAMP2 in the same vesicles (P < 0.0001). Furthermore, the presence of AQP2 in vesicles immunoisolated with anti-VAMP2 antibodies was confirmed by immunoblotting. In conclusion, VAMP2, a component of the neuronal SNARE complex, is expressed in vesicles carrying AQP2, suggesting a role in vasopressin-regulated vesicle trafficking of AQP2 water channels.

Animals↗
PubMed1995

The levels of ubiquitinated histone H2A are highly upregulated in transformed human cells: partial colocalization of uH2A clusters and PCNA/cyclin foci in a fraction of cells in S-phase.

The levels and distribution of ubiquitinated histone H2A (uH2A) have been studied in normal and transformed human cells using a monoclonal antibody (mAb E6C5) that reacts specifically with this ubiquitin conjugate as determined by two-dimensional gel western blotting and microsequencing. Immunoblotting experiments demonstrated that the levels of the protein are highly upregulated in SV40-transformed human fibroblasts (WI-38 SV40) and keratinocytes (K14) relative to their normal counterparts, a finding that was further confirmed by indirect immunofluorescence studies of formaldehyde/Triton X-100-treated cells, which showed that about 97% of the transformed cells and 26% of the normal populations reacted with the antibody to yield a fine granular nuclear staining associated with the chromatin. Transformed cells contained in addition clusters of uH2A that were quite abundant and that showed variable size, shape and distribution even within a single cell line. The clusters, which were rare in normal cells, did not colocalize with other known nuclear antigens and may correspond to novel nuclear domains where ubiquitination/deubiquitination takes place. Electron microscopic immunocytochemistry of K14 cells confirmed the existence of the clusters. Double immunofluorescence studies of K14 keratinocytes with proliferating cell nuclear antigen (PCNA)/cyclin antibodies, which react with the nuclei of cells engaged in DNA replication, showed partial colocalization of PCNA/cyclin foci and large uH2A clusters in about 14% of the S-phase cells, and these corresponded mainly to late S-phase cells. Inhibition of DNA replication with hydroxyurea resulted in an overall increase in the intensity of the uH2A staining as well as in a more clear colocalization of uH2A clusters and PCNA/cyclin foci. Taken together, the results support the contention that uH2A plays a role at some stage of DNA replication.

Amino Acid Sequence↗
PubMed1995

Albuminuria and 24-h ambulatory blood pressure in normoalbuminuric and microalbuminuric NIDDM patients. A longitudinal study.

OBJECTIVE: To assess the long-term relationships between 24-h ambulatory blood pressure (AMBP), urinary albumin excretion (UAE) rate, and metabolic control in non-insulin-dependent diabetes mellitus (NIDDM) patients with normo- and microalbuminuria. RESEARCH DESIGN AND METHODS: We conducted a prospective study of 23 NIDDM patients (11 with normoalbuminuria and 12 with microalbuminuria) receiving standard clinical care, including antihypertensive treatment, attending the outpatient clinic and 8 healthy control subjects. Twenty-four-hour AMBP and UAE were measured synchronously in addition to fasting plasma glucose, HbA1c, and serum creatinine at baseline and after 4.6 (4.2-5.1) years [mean (range)]. RESULTS: Baseline systolic, but not diastolic, 24-h AMBP was significantly higher in diabetic patients compared with control subjects (146/80 [16/11] vs. 133/78 [9/9] mmHg, P < 0.05), but was similar in normoalbuminuric (143/81 [11/11] mmHg) and microalbuminuric (148/80 [20/10] mmHg) patients during strict blood pressure control. The annual increase in 24-h AMBP was equivalent in diabetic patients (0.6/-0.2 [2.6/1.5] mmHg/year) and control subjects (0.7/0.2 [1.2/1.4] mmHg/year, NS) and not significantly different from zero. Overall UAE did not change in control subjects (5.6 [1.6] vs. 4.4 [1.9]) (geometric mean [antilog SD]) or in the normoalbuminuric (8.7 [1.7] vs. 11.3 [3.0] micrograms/min) and microalbuminuric (35.7 [2.1] vs. 34.5 [3.2] micrograms/min) patients. In diabetic patients, the annual change in UAE correlated significantly with the annual change in the systolic (r = 0.61, P < 0.002) and diastolic (r = 0.54, P < 0.008) 24-h AMBP. In microalbuminuric patients, only the annual increase in systolic 24-h AMBP correlated significantly with the annual change in UAE (r = 0.71, P = 0.010), whereas in the normoalbuminuric patients, only the annual increase in diastolic 24-h AMBP and the annual change in UAE were significantly correlated (r = 0.66, P = 0.026). In a stepwise multiple linear regression analysis, the annual progression in albuminuria in NIDDM patients was significantly determined by increases in systolic (parameter estimate 0.018, SE 0.006, P < 0.008) as well as in diastolic 24-h AMBP (parameter estimate 0.026, SE 0.011, P < 0.033). CONCLUSIONS: In an outpatient clinical setting, 24-h AMBP is similar in NIDDM patients with normo- and microalbuminuria. Alterations in both 24-h AMBP and UAE are on average moderate and equivalent compared with those in healthy control subjects. Although the average change in albuminuria is small, a progression in albuminuria relates to increments in both systolic and diastolic 24-h AMBP.

Albuminuria↗
PubMed1995

Similar insulin sensitivity in NIDDM patients with normo- and microalbuminuria.

OBJECTIVE: To investigate whether insulin resistance and microalbuminuria are associated in non-insulin-dependent diabetes mellitus (NIDDM). RESEARCH DESIGN AND METHODS: Insulin sensitivity was assessed using a hyperinsulinemic euglycemic clamp in 11 normoalbuminuric and 9 microalbuminuric NIDDM patients matched for sex, age, body composition, glycemic control, diabetes duration, and therapy. RESULTS: Isotopically determined glucose disposal was similar in normo- and microalbuminuric patients in the basal state (mean +/- SD; 3.30 +/- 1.01 vs. 3.46 +/- 0.82 mg.kg lean body mass [LBM]-1.min-1; NS) and during hyperinsulinemia (7.16 +/- 2.65 vs. 6.63 +/- 2.88 mg.kg LBM-1.min-1;NS). No difference was observed in nonoxidative glucose disposal or lipid oxidation. Endogenous glucose production was equally suppressed by insulin (-0.08 +/- 0.99 vs. 0.30 +/- 1.12 mg.kg-1 LBM.min-1; NS). Glucose oxidation tended to be lower in the normoalbuminuric patients in the basal state (1.16 +/- 0.37 vs. 1.41 +/- 0.36 mg.kg LBM-1.min-1) and during hyperinsulinemia (2.35 +/- 0.72 vs. 2.90 +/- 0.77 mg.kg LBM-1.min-1; both P < 0.15). Urinary albumin excretion rate correlated with the insulin-stimulated glucose oxidation rate (r = 0.59, P = 0.0064), and a similar trend was seen in the basal state (r = 0.42, P = 0.063). Protein oxidation was higher in normoalbuminuric patients (1.6 +/- 0.5 vs. 1.0 +/- 0.4 mg.kg LBM-1.min-1; P = 0.017) and correlated inversely with albuminuria (r = -0.70, P = 0.0007). Serum growth hormone increased during insulin infusion; however, the increase was significantly greater in microalbuminuric patients. Plasma lipoproteins, maximal aerobic capacity, and 24-h ambulatory blood pressure were similar in the two groups. CONCLUSIONS: Basal and insulin-stimulated glucose uptakes are comparable in carefully matched normo- and microalbuminuric NIDDM patients, and glucose oxidation may be positively related to albuminuria. The inverse relation between protein oxidation and albuminuria may be due to higher growth hormone levels during daily life perturbations in glucose in microalbuminuric patients.

Albuminuria↗
PubMed1995

Is misoprostol the drug of choice for induced cervical ripening in early pregnancy termination?

BACKGROUND: To study the effectiveness of three different cervical ripening agents in terms of dilatation ability and patient discomfort in connection with legal first trimester abortion. METHODS: Three randomized trials among unselected nulliparous women were performed 1: hygroscopic tent versus gemeprost, 2: misoprostol versus gemeprost and 3: misoprostol administered orally 17 versus 10 hours before vacuum curettage was performed. MAIN OUTCOMES: Dilatation ability, frequent gastrointestinal side effects, severe pain (patients' perception). RESULTS: In Trial 1, there was a tendency of a greater dilatation ability using the hygroscopic tent, while the experience of pain was a greater problem with gemeprost. In Trials 2 and 3, there were no significant differences in the dilatation abilities or gastrointestinal patient discomfort. There was a tendency towards a higher demand for narcotic analgesics in patients treated with gemeprost compared with all other groups. CONCLUSIONS: Gemeprost and misoprostol showed almost identical ability to dilate and caused patient-experienced discomfort to the same degree. The use of misoprostol may be preferred as it has the advantage of being both less expensive and easier to administer.

Abortifacient Agents, Nonsteroidal↗
PubMed1995

Effects of microtubule disruption on endocytosis, membrane recycling and polarized distribution of Aquaporin-1 and gp330 in proximal tubule cells.

Microtubules are critically involved in membrane traffic and maintenance of epithelial cell polarity. In this study we examined the effect of microtubule disruption by colchicine on 1) the subcellular organization of the apical endocytic apparatus, 2) apical endocytosis, and 3) subcellular distribution of gp330 and Aquaporin-1 water channels in renal proximal tubule cells. Rats were treated in vivo with colchicine for 5 h before fixation of the kidneys, and sections of proximal tubules were studied using electron microscopy, morphometry and immunocytochemistry. In proximal tubule cells from colchicine-treated animals, virtually no endocytic invaginations are present, indicating that colchicine blocks the formation of endocytic invaginations. Furthermore, no large endocytic vacuoles are present, also consistent with a block of endocytosis. This was confirmed by functional studies revealing a colchicine-induced arrest in apical endocytosis of peroxidase. There is a marked reduction in dense apical tubules (the exocytic vehicle for membrane recycling) but an extensive accumulation of small vesicles, suggesting a disruption in membrane recycling. This disruption may be primary or secondary to the block of endocytosis. Immunofluorescence and immunoelectron microscopy reveal extensive colchicine-induced changes in the subcellular distribution of gp330 and Aquaporin-1. The localization of gp330 is normally restricted to the apical endocytic apparatus. However, after colchicine treatment gp330 is localized to numerous vesicles distributed throughout the entire cytoplasm, as previously shown (Gutmann et al., Am. J. Physiol. 257, C397-C407 (1989). Also Aquaporin-1 water channels, which are normally almost exclusively present in the plasma membranes, are redistributed to small vesicles in addition to the plasma membrane localization after colchicine treatment. In summary, the present study suggests that cytoplasmic microtubules are critically involved in 1) formation and stabilization of endocytic invaginations, 2) formation of large endocytic vacuoles, 3) apical endocytosis, 4) maintaining the polarized distribution of vesicles in the apical part of the cell, and 5) maintaining the polarized organization of gp330 in the apical endocytic apparatus, and maintaining Aquaporin-1 water channels in the plasma membranes.

Animals↗
PubMed1995

Segmental distribution of the endocytosis receptor gp330 in renal proximal tubules.

The subcellular distribution and segmental variations in location of gp330, a scavenger receptor for filtered proteins in renal proximal tubules, was analyzed. Kidney tissue from rats (4 different strains), rabbits and humans were analyzed by light- and electron microscope immunocytochemistry, using cryosections or Lowicryl sections from cryosubstituted tissue. Gp330 was located mainly in apical coated pits, small and large endocytic vacuoles and in dense apical tubules in the proximal tubule cells. The labeling density was markedly higher in segments 1 and 2 as compared to segment 3 of the proximal tubule. In addition to the location in the early part of the endocytic pathway, gp330 was also present in lysosomes, especially in segments 1 and 2. The lysosomal labeling was not restricted to the membrane, but was also seen in the matrix. Localization of gp330 in lysosomes was confirmed on sections from purified lysosomal fractions from rat renal cortex. The brush border localization of gp330 in proximal tubules exhibited a characteristic segmental variation. In the initial part of segment 1, there was virtually no brush border labeling. In the remaining part of segment 1 and in segment 2, there was a distinct but sometimes patchy labeling of the brush border. In segment 3, groups of microvilli of approximately 10 as seen in sections were intensively labeled from bottom to tip and there were often more than one of these groups on a single cell, the remaining microvilli were unlabeled. No differences in the cellular and subcellular localization of gp330 were observed between species or rat strains. In conclusion, the present study demonstrates that in addition to its location in the early endocytic and recycling pathway, gp330 is also present in microvilli and the protein and degradation products thereof is present in lysosomes, consistent with its role as a protein scavenger receptor.

Animals↗
PubMed1994

Regulation of collecting duct water channel expression by vasopressin in Brattleboro rat.

AQP-CD is a vasopressin-regulated water channel expressed exclusively in the renal collecting duct. We have previously shown that AQP-CD is present in the apical plasma membrane and subapical vesicles of collecting duct cells, consistent with membrane-shuttling mechanisms that have been proposed to explain the short-term action of [Arg8] vasopressin (AVP) to regulate apical water permeability. We propose here that AVP may also have long-term actions on the collecting duct to regulate the expression of the AQP-CD water channel. We used immunoblotting, immunohistochemistry, and in vitro perfusion of renal tubules to investigate water channel regulation in collecting ducts of diabetes insipidus (Brattleboro) rats treated with a 5-day infusion of AVP or vehicle. Immunoblotting and immunohistochemistry demonstrated that collecting ducts of vehicle-infused Brattleboro rats had markedly reduced expression of AQP-CD relative to normal rats. In response to AVP infusion there was a nearly 3-fold increase in AQP-CD expression as detected by immunoblotting. Immunocytochemistry demonstrated that the increased expression was predominantly in the apical plasma membrane and subapical vesicles of collecting duct cells. Inner medullary collecting ducts of AVP-infused Brattleboro rats displayed a 3-fold increase in osmotic water permeability relative to vehicle-infused controls, in parallel with the change in AQP-CD expression. Based on these findings, we conclude that (i) long-term infusion of AVP, acting either directly or indirectly, regulates expression of the AQP-CD water channel and (ii) AQP-CD is the predominant AVP-regulated water channel.

Animals↗