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M L Zeidel

Publications and source records attributed to M L Zeidel.

At least 55 records · Page 3Linked to original sources
PubMed1994

Characterization of purified endosomes containing the antidiuretic hormone-sensitive water channel from rat renal papilla.

Antidiuretic hormone (ADH) stimulation of renal epithelial cells elicits a large increase in apical membrane osmotic water permeability (Pf) produced by the fusion of water channel containing vesicles with the apical membrane. Removal of ADH stimulation results in retrieval of apical water channels into a specialized non-acidic endosomal compartment. Previous studies (Sabolic, I., Wuarin, F., and Shi, L. B. (1992) J. Cell Biol. 119, 111-122) have shown that water channel containing papillary endosomes labeled with fluorescein-dextran can be isolated from rat renal papilla. We have utilized small particle flow sorting methodology to both monitor and improve upon the purification of these water channel containing endosomes (WCV). Flow cytometry analysis on a vesicle-by-vesicle basis demonstrates that WCV are homogeneous with respect to entrapped fluorescein-dextran, the apical membrane enzyme marker leucine amino peptidase and ultrastructural morphology. WCV do not acidify their luminal contents after addition of Mg-ATP but contain abundant functional water channels (Pf0.28 cm/s at 23 degrees C) as determined by stopped flow fluorimetry. SDS-polyacrylamide gel electrophoresis analysis shows that purified WCV are composed of 20 major protein bands. To determine the identity of WCV water channels, WCV proteins were probed with affinity purified antisera recognizing two renal water channel proteins. These include Aquaporin-CHIP found in the proximal tubule and thin descending limb of Henle and the candidate ADH water channel protein WCH-1 or Aquaporin- (AQP) CD present in the ADH-responsive epithelial cells of the collecting duct. These data reveal that WCV contained little or no AQP-CHIP protein. In contrast, WCV are highly enriched for AQP-CD protein. Together, these data define the protein composition of the papillary WCV and link directly the presence of functional apical membrane water channels with the presence of the AQP-CD protein.

Animals↗
PubMed1994

Ultrastructure, pharmacologic inhibition, and transport selectivity of aquaporin channel-forming integral protein in proteoliposomes.

Reconstitution of highly purified aquaporin CHIP (channel-forming integral protein) into proteoliposomes was previously shown to confer high osmotic water permeability (Pf) to the membranes [Zeidel et al. (1992) Biochemistry 31, 7436-7440]. Here we report detailed ultrastructural, pharmacologic, and transport studies of human red cell CHIP in proteoliposomes. Freeze-fracture and transmission electron microscopy revealed a uniform distribution of CHIP which was incorporated into the membranes in both native and inverse orientations. Morphometric analysis of membranes reconstituted at three different concentrations of CHIP revealed that the intramembrane particles correspond to tetramers or possible higher order oligomers, and the Pf increased in direct proportion to the CHIP density. Proteolytic removal of the 4-kDa C-terminal cytoplasmic domain of CHIP did not alter the Pf or oligomerization in red cell membranes. CHIP exhibited a similar conductance for water when reconstituted into membranes of varied lipid compositions. The sensitivities of CHIP-mediated Pf to specific sulfhydryl reagents were identical to known sensitivities of red cell Pf, including a delayed response to p-(chloromercuri)benzenesulfonate. CHIP did not increase the permeability of the proteoliposome membranes to H+/OH- or NH3. These studies demonstrate that CHIP proteoliposomes exhibit all known characteristics of water channels in native red cells and therefore provide a defined system for biophysical analysis of transmembrane water movements.

Aquaporin 1↗
PubMed1994

Biologically active two-dimensional crystals of aquaporin CHIP.

Plasma membranes of several mammalian tissues are highly permeable to water due to the presence of CHIP, the 28-kDa channel-forming integral protein which is the archetypal member of the aquaporin family of water channel proteins. To define its native structure, purified red cell CHIP protein was reconstituted into lipid bilayers at a high protein-to-lipid ratio, and the resulting 3-microns diameter membrane vesicles were examined by high resolution electron microscopy. The reconstituted membranes contained highly ordered two-dimensional crystalline lattices of p422(1) symmetry in which each CHIP tetramer contained a central depression extending from the outer and inner surfaces of the membrane into the transbilayer domain of the molecule. The reconstituted membranes also exhibited extremely high osmotic water permeability, Pf = 0.472 cm/s, corresponding to the sum of activities of all incorporated CHIP molecules. These studies report the first two-dimensional crystallization of a biologically active water channel and provide direct evidence of the structure responsible for its pore-like behavior.

Aquaporin 1↗
PubMed1994

Permeability properties of rat renal lysosomes.

Although lysosomes maintain large pH gradients and may be subjected to significant osmotic gradients in vivo, little is known about their passive permeability properties. In recent studies, vacuolar H(+)-adenosine-triphosphatases (ATPases), such as those found in lysosomes, have been suggested to act as water channels. In addition, the erythrocyte and proximal tubule water channel CHIP28 is present on the plasma membrane of proximal tubule cells and may undergo endocytosis so that it is incorporated in lysosomes. We therefore examined water, proton, and small nonelectrolyte permeabilities in freshly purified lysosomes from rat renal proximal tubule. Lysosomes were purified by differential and Percoll gradient centrifugation. The preparation contained only lysosomes when examined by electron microscopy. Moreover, analysis by flow cytometry showed virtually all particles to be positive for acid phosphatase and cathepsin B activities. Permeabilities were measured on a stopped-flow fluorimeter by monitoring the self-quenching or pH-sensitive quenching of entrapped fluorescein derivatives. Osmotic water permeability (Pf) averaged 0.011 +/- 0.003 cm/s (n = 6), a value similar to that of biological membranes containing water channels. However, Pf was insensitive to the organic mercurial reagent p-chloromercuribenzene-sulfonate and to HgCl2 and exhibited an activation energy of 10.8 +/- 0.8 kcal/mol. These results indicate that water flux in lysosomes occurred via the lipid bilayer, and not via water channels. Addition of ATP led to lysosomal acidification (proton flux = 4.6 +/- 0.8 x 10(-11) mmol H+.s-1.cm-2), which was completely inhibited by 0.1 microM bafilomycin. Pf was insensitive to this agent as was the passive proton permeability (0.36 +/- 0.18 cm/s, n = 4). Permeabilities to small nonelectrolytes varied in proportion to the oil-water partition coefficient, confirming the applicability of Overton's rule to lysosomes. We conclude that proximal tubular lysosomes exhibit high Pf, which occurs via the lipid bilayer and not via vacuolar H(+)-ATPase.

Acids↗
PubMed1994

Determinants of apical membrane permeabilities of barrier epithelia.

Renal collecting duct and thick ascending limb, as well as stomach, exhibit strikingly low permeabilities to water and solutes. However, the apical membrane characteristics responsible for these unique permeabilities remain unknown. While the lipid composition of artificial membranes governs membrane permeability, exoplasmic and cytoplasmic leaflets of biological apical membranes exhibit striking asymmetries in lipid composition. This asymmetry, as well as the presence of membrane proteins, may be critical to barrier function. To determine the role of bulk lipid composition in apical membrane barrier function, we compared permeabilities to water (Pf), protons, ammonia, and several small nonelectrolytes of gastric apical membrane vesicles [native gastric vesicles (NGV)] and liposomes prepared from lipids quantitatively extracted from these vesicles [gastric lipid large unilamellar vesicles (LUV)]. Permeabilities were measured on a stopped-flow fluorimeter by monitoring self- or pH-sensitive quenching of entrapped carboxyfluorescein. NGV exhibited low Pf (2.8 +/- 0.3 x 10(-4) cm/s) while gastric lipid LUV Pf averaged 1.2 +/- 0.1 x 10(-3) cm/s, a fourfold increase compared with the value in NGV. Gastric lipid LUV also demonstrated higher permeabilities to protons, ammonia, propylene glycol, butyramide, ethanolamine, and acetamide compared with values in NGV. In contrast, gastric lipid LUV exhibited the same or lower permeabilities to urea, glycerol, and ammonia compared with values in NGV. We conclude that lipid composition alone can reconstitute membrane permeabilities to some, but not all, molecules. These results indicate that bilayer asymmetry may be required for the unique permeability of "water-tight" apical membranes and reveal different barrier mechanisms for water and protons, as opposed to ammonia, urea, and glycerol.

Cell Membrane Permeability↗
PubMed1994

Permeability properties of the mammalian bladder apical membrane.

The luminal surface of mammalian bladder is exposed to urine with a composition widely different from that of plasma that bathes the basolateral surface of epithelium. Therefore we predict that the bladder permeability barrier, which is likely located in the apical membrane (AM), will exhibit low permeabilities to water, urea, NH3, H+, and small nonelectrolytes. AM surface area increases as the bladder fills with urine and decreases during emptying, a process that involves cyclical endocytosis and reinsertion of membrane from a pool of AM endosomes (AME). Rigid-appearing plaques composed of three proteins, uroplakins, have been identified and occupy 70-90% of AM surface area. To determine permeability properties of the AM permeability barrier, we purified AME and measured their permeabilities. Rabbit urinary bladders were removed, and their apical surface was exposed to carboxyfluorescein (CF) or horseradish peroxidase (HRP). Exposure to hypotonic and then isotonic basolateral solutions induced endocytosis of luminal CF or HRP into AME. Electron microscopy of bladders after this treatment revealed HRP entrapped within AME bordered by plaques. AME were purified by differential and sucrose-gradient centrifugation, and CF-containing AME were purified 17.0 +/- 3-fold (SD) with respect to homogenate. Analysis of purified AME by flow cytometry showed that > 95% of vesicles contained CF entrapped from luminal solution and were selectively labeled with anti-uroplakin antibody. AME osmotic water permeability averaged 2.3 +/- 0.66 x 10(-4) cm/s and exhibited a high activation energy, indicating that AM contains no water channels. Permeability to urea and NH3 averaged 7.8 +/- 3.7 x 10(-7) and 1.5 +/- 0.3 x 10(-3) cm/s, respectively, which are exceptionally low and similar to permeabilities of other water-tight membranes, including toad urinary bladder and gastric mucosa. AME behaved as a single population in all permeability studies, which will permit future characterization of protein and lipid structure responsible for these unique permeability properties.

Ammonia↗
PubMed1994

Human red cell Aquaporin CHIP. II. Expression during normal fetal development and in a novel form of congenital dyserythropoietic anemia.

Channel-forming integral protein (CHIP) is the archetypal member of the Aquaporin family of water channels. Delayed CHIP expression was shown recently in perinatal rat (Smith, B. L., R. Baumgarten, S. Nielsen, D. Raben, M. L. Zeidel, and P. Agre. 1993. J. Clin. Invest. 92:2035-2041); here we delineate the human patterns. Compared with adult, second and third trimester human fetal red cells had lower CHIP/spectrin ratios (0.72 +/- 0.12, 0.94 +/- 0.22 vs 1.18 +/- 0.11) and reduced osmotic water permeability (0.029, 0.026 vs 0.037 cm/s); CHIP was already present in human renal tubules by the second trimester. A patient with a novel form of congenital dyserythropoietic anemia (CDA) with persistent embryonic and fetal globins and absent red cell CD44 protein was studied because of reduced CHIP-associated Colton antigens. Novel CDA red cells contained < 10% of the normal level of CHIP and had remarkably low osmotic water permeability (< 0.01 cm/s), but no mutation was identified in Aquaporin-1, the gene encoding CHIP. These studies demonstrate: (a) unlike rat, human CHIP expression occurs early in fetal development; (b) red cell water channels are greatly reduced in a rare phenotype; and (c) disrupted expression of red cell CHIP and CD44 suggests an approach to the molecular defect in a novel form of CDA.

Adult↗
PubMed1993

Isolation of highly purified, functional endosomes from toad urinary bladder.

Endosomes are difficult to isolate as they share size and density properties with much more abundant cellular organelles such as mitochondria. In cultured cell lines the tandem use of charge-dependent isolation techniques and differential centrifugation is necessary to isolate endosomes. Endosomal populations of the toad urinary bladder are of special interest because they are thought to contain a water channel. Understanding of the molecular structure of the water channel has been constrained, as there is currently no practical method to isolate functional water-channel-containing vesicles. This study reports the tandem use of charge-dependent techniques and centrifugation to isolate populations of endosomes from the toad urinary bladder. To purify water-channel-containing vesicles aqueous two-phase partition was utilized to fractionate a preparation partially purified by differential centrifugation. Populations of endosomes were analysed by small-particle flow cytometry techniques. A 5-fold enrichment in endosomes, achieved with aqueous two-phase partition, allowed us to identify two populations of endosomes of diverse size in a toad bladder endosomal fraction. Preenrichment also improved the efficiency of flow cytometry sorting, allowing isolation of the two endosomal populations in sufficient quantities for secondary analysis. A population of larger endosomes had very high water permeability, indicating the presence of water channels. The two populations had different SDS/PAGE fingerprints. Electron micrographs of the flow-sorted material shows a uniform population of membrane vesicles devoid of mitochondria and other identifiable cellular organelles. Hence, aqueous two-phase partition and flow cytometry allow identification of two populations of endosomes in the toad urinary bladder which have diverse structural and functional properties. Isolation of functional water-channel-containing vesicles allows co-localization of water-channel function with candidate water-channel proteins.

Animals↗
PubMed1993

Apical membrane of the gastric parietal cell: water, proton, and nonelectrolyte permeabilities.

Gastric parietal cell apical membranes must protect the cell from the extremely low pH and wide variations in osmolality of the gastric juice. To characterize the permeability properties of gastric apical membranes, we have measured passive permeabilities to water, protons, NH3, and small nonelectrolytes of membrane vesicles derived from parietal cells of fasted animals and fed animals. Both preparations are known to be highly enriched in H+/K(+)-ATPase, the enzyme responsible for acidifying the gastric contents. The preparations behaved as single populations, and their permeability properties were similar in all respects, permitting pooling of the results. This similarity suggests that insertion of tubulovesicles into the apical membrane does not change the behavior of the lipid bilayer. Osmotic water permeability (Pf) averaged (mean +/- SD) (2.8 +/- 0.3) x 10(-4) cm/s, a value 10-fold lower than that obtained in lecithin large unilamellar vesicles (LUV) and similar to that obtained in other water-tight epithelia. Similarly, ammonia permeability (PNH3) was low [(4.4 +/- 2.3) x 10(-3) cm/s] and 10 times below that of lecithin LUV. By contrast, proton permeability (PH+) was surprisingly high (0.030 +/- 0.011 cm/s) and similar to that of lecithin LUV. These results suggest that the pathway for proton permeation differs from that of water and NH3. Nonelectrolyte permeabilities were strikingly similar to those obtained in another water-tight epithelium, the toad urinary bladder. Moreover, these permeabilities followed Overton's rule in that permeability varied in accordance with the oil-water partition coefficient. We conclude that the gastric apical membrane, like that of several renal epithelia, is relatively water-tight and exhibits low permeabilities to small nonelectrolytes. These properties are likely to be essential to the ability of this membrane to perform its barrier function.

Ammonia↗
PubMed1993

The molecular structure of the antidiuretic hormone elicited water channel.

Measurements of osmotic water permeability (Pf) have shown that the plasma membranes of human red cells and certain epithelial cells possess specialized water channels. Although these water channels have been characterized extensively using biophysical techniques, the proteins that compose these unique channels have only recently been identified. Antidiuretic hormone (ADH) stimulation rapidly increases collecting duct epithelial cell Pf by fusion of water channel-containing vesicles (WCV) with their apical membranes. The proteins of WCV from toad bladder and rodent kidney have been characterized. The principal proteins in toad bladder WCV are 55,000 daltons (55 kDa) and 53 kDa and span the lipid bilayer of these vesicles. Polyclonal antisera raised against the 55-kDa and 53-kDa proteins inhibit ADH-stimulated toad bladder Pf by 80% and recognize protein bands of 46, 38 and 30 kDa in mouse kidney. Purification of WCV from rat kidney reveals enrichment of the 46-kDa protein. Recently, a 28-kDa integral membrane protein (called CHIP-28) has been isolated from human red cells. It forms functional water channels in Xenopus oocytes and when reconstituted into proteoliposomes. Large amounts of CHIP-28 protein are present in epithelial cells of the proximal tubule and descending thin limb of Henle's loop. Molecular cloning efforts are underway to elucidate the structure and function of these candidate water channel proteins.

Animals↗
PubMed1993

Water channels.

The movement of water across cell membranes has been an active area of research for more than 100 years and is of fundamental importance in the normal water metabolism of all terrestrial animals. The objective of this review is to integrate recent data obtained from the isolation and molecular cloning of water channel proteins, with functional information provided by biophysical measurements of membrane water transport. Whereas the water permeability of most cell membranes can be accounted for by the diffusion of water across the lipid bilayer, other cells, including the erythrocyte as well as certain cells in renal epithelia, possess specialized water channels. Water channels are composed of specialized proteins that create highly selective aqueous pores across cell membranes. Data concerning the distribution, permeability, and function of these various water channels will greatly enhance our knowledge of how water is transported across cell membranes.

Amino Acid Sequence↗
PubMed1993

Fate of antidiuretic hormone water channel proteins after retrieval from apical membrane.

In toad bladder granular cells, antidiuretic hormone (ADH) stimulates insertion of vesicles containing water channels (WCV), markedly increasing apical membrane osmotic water permeability (Pf). After withdrawal of ADH stimulation, WCV are removed from the apical membrane and fluid-phase markers endocytosed from the apical solution appear predominantly in endosomes at 10-15 min and multivesicular bodies at 30-60 min. Although the luminal contents of this endocytic pathway have been well characterized, the fate of membrane proteins, including functional ADH water channels in these vesicles remains unclear. Using electron microscopic, flow cytometric, and stopped-flow fluorescence measurements and characterization of labeled vesicle proteins, we examined the fate of membrane proteins contained within WCV. The protein complements of endosomes harvested after 10, 30, and 60 min of ADH withdrawal were similar. Selective covalent labeling of apical proteins during ADH stimulation followed by ADH reversal for 30 or 60 min showed that apical proteins colocalize with fluid-phase marker-labeled endosomes at all times, and most apically labeled protein bands present in the 10-min fraction were also present in the 30- and 60-min endosome fractions. Endosomes at 10 and 30 min but not at 60 min contained functional water channels revealed by high Pf and proton permeability, low activation energy of Pf, and sensitivity of Pf to mercurial reagents. We conclude that a portion of apically exposed membrane proteins, including candidate water channel proteins, travel together with fluid-phase markers from 10-min endosomes into later endosomal compartments. Functional water channels may be inactivated or some essential protein component selectively sorted away between 30 and 60 min after ADH withdrawal.

Animals↗
PubMed1993

Transport defects of rabbit inner medullary collecting duct cells in obstructive nephropathy.

Urinary obstruction markedly reduces collecting duct Na+ reabsorption. To define the cellular mechanisms of this derangement in Na+ reabsorption in inner medullary collecting duct (IMCD) of obstructed kidneys, suspensions of intact IMCD cells and inner medulla plasma membranes (IMPM) were prepared from 24 h obstructed and untreated control kidneys. Oxygen consumption (QO2) studies revealed marked reductions in both amiloride-sensitive and ouabain-sensitive QO2 but not ouabain-insensitive QO2 in intact IMCD cells from obstructed, compared with control animals, indicating a reduction in oxygen-dependent transport activities of both the Na+ channel and the Na(+)-K(+)-adenosinetriphosphatase (ATPase). Amiloride-sensitive conductive 22Na+ uptake in intact IMCD cells from obstructed kidneys was significantly decreased by 45% at 10 s, 30 s, and 1-5 min (10 s: 2.42 +/- 0.63 vs. 4.49 +/- 0.64 nmol Na+ flux/mg protein, n = 7, P < 0.05; 1 min: 4.65 +/- 0.7 vs. 8.27 +/- 0.98 nmol Na+ flux/mg protein, n = 7, P < 0.05), indicating decreased activity of amiloride-sensitive Na+ channels in these cells. However, immunoblots of IMPM with antibodies to Na+ channel proteins did not show significant differences in content of Na+ channel proteins between membranes from obstructed and control groups. Ouabain-sensitive Na(+)-K(+)-ATPase activity in IMPM of obstructed kidneys was also reduced (61.1 +/- 18.1 vs. 152.6 +/- 25.8 nmol ATP degradation.min-1.mg protein-1, n = 6, P < 0.02), and immunoblots with monoclonal antibodies against the alpha 1- and beta-subunits of rabbit Na(+)-K(+)-ATPase showed a 51 +/- 7% reduction of both subunits in IMPM from obstructed kidneys (n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Hormonal regulation of inner medullary collecting duct sodium transport.

The inner medullary collecting duct (IMCD) is the final arbiter of renal Na+ excretion, and Na+ transport in this segment is controlled by a wide variety of hormones and renal autacoids. This review examines the mechanisms of IMCD Na+ transport and its regulation using results obtained from micropuncture and microcatheterization studies in the intact animal, as well as data from isolated perfused tubules, freshly prepared cell suspensions, and cultured IMCD cells. Where appropriate, results from closely related tissues such as the cortical collecting duct and model urinary epithelia are examined. Na+ reabsorption in this segment occurs predominantly via apical amiloride-sensitive Na+ channels and basolateral Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase). Although there is some evidence for the activities of other transporters such as Na(+)-K(+)-2Cl- and Na-Cl cotransporters and Na+/H+ exchanger, their role in Na+ homeostasis remains undefined. Mineralocorticoids augment the activities of both apical Na+ channels and basolateral Na(+)-K(+)-ATPase by a variety of complex mechanisms. Prostaglandin E2 inhibits Na(+)-K(+)-ATPase and appears to mediate the actions of several peptide hormones, including endothelin, interleukin-1, and atrial natriuretic peptide [ANP-(31-67)]. Several peptides in the ANP family [ANP-(99-126), urodilatin, and brain natriuretic peptide] bind to guanylate cyclase-linked receptors, leading to inhibition of apical Na+ channel function. These mechanisms of regulation of IMCD Na+ transport likely play important roles in total body Na+ balance in health and disease.

Animals↗
PubMed1993

Transport defects of rabbit medullary thick ascending limb cells in obstructive nephropathy.

To characterize the sodium transport defect responsible for salt wasting in obstructive nephropathy, the major sodium transporters in the medullary thick ascending limb (mTAL), the apical Na-K-2Cl cotransporter and the basolateral Na-K-ATPase, were studied in fresh suspensions of mTAL cells and outer medulla plasma membranes prepared from obstructed and untreated kidneys. Oxygen consumption (QO2) studies in intact cells revealed marked reductions in the inhibitory effects of both furosemide and ouabain on QO2 in cells from obstructed, as compared with control animals, indicating a reduction in activities of both the Na-K-2Cl cotransporter and the Na-K-ATPase. Saturable [3H]bumetanide binding was reduced in membranes isolated from obstructed kidneys, but the Kd for [3H]bumetanide was unchanged, indicating a decrease in the number of functional luminal Na-K-2Cl cotransporters in obstructed mTAL. Ouabain sensitive Na-K-ATPase activity in plasma membranes was also reduced, and immunoblots using specific monoclonal antibodies directed against the alpha and beta subunits of rabbit Na-K-ATPase showed decreased amounts of both subunits in outer medullas of obstructed kidney. A significant decrease in [3H]bumetanide binding was detected after 4 h of ureteral obstruction, whereas Na-K-ATPase activity at this time was still not different from control. We conclude that ureteral obstruction reduces the amounts of both luminal Na-K-2Cl cotransporter and basolateral Na-K-ATPase in mTAL of obstructed kidney and that these reductions contribute to the salt wasting observed after release of obstruction.

Animals↗
PubMed1993

Concurrent expression of erythroid and renal aquaporin CHIP and appearance of water channel activity in perinatal rats.

Major phenotypic changes occur in red cell membranes during the perinatal period, but the underlying molecular explanations remain poorly defined. Aquaporin CHIP, the major erythroid and renal water channel, was studied in perinatal rats using affinity-purified anti-CHIP IgG for immunoblotting, flow cytometry, and immunofluorescence microscopy. CHIP was not detected in prenatal red cells but was first identified in circulating red cells on the third postnatal day. Most circulating red cells were positive for CHIP by the seventh postnatal day, and this proportion rose to nearly 100% by the 14th day. The ontogeny of red cell CHIP correlated directly with acquisition of osmotic water permeability and inversely with Arrhenius activation energy. Only minor alterations in the composition of red cell membrane lipids occurred at this time. Immunohistochemical analysis of perinatal kidneys demonstrated a major induction of CHIP in renal proximal tubules and descending thin limbs at birth, coincident with the development of renal concentration mechanisms. Therefore, water channels are unnecessary for oxygen delivery or survival in the prenatal circulation, however CHIP may confer red cells with the ability to rehydrate rapidly after traversing the renal medulla, which becomes hypertonic after birth.

Aging↗
PubMed1993

Differential actions of cisplatin on renal proximal tubule and inner medullary collecting duct cells.

Cisplatin (CP) nephrotoxicity in vivo is characterized by proximal tubule (PT) and collecting duct dysfunction. We reported previously that mitochondrial injury is an important early event in CP toxicity to PT cells and precedes inhibition of Na+,K(+)-ATPase activity and loss of cell K+. In the present study, we monitored oxygen consumption (QO2) and net K+ fluxes in intact inner medullary collecting duct (IMCD) and PT cells in vitro, using O2- and K(+)-sensitive electrodes, to determine if CP has similar effects on IMCD cells. Short-term exposure of IMCD cells to CP resulted in inhibition of spontaneous, ouabain-sensitive and ouabain-oversensitive QO2, but to a lesser degree than in PT. Ouabain-sensitive K+ transport and cell K+ content were also reduced in intact IMCD cells in this setting, confirming inhibition of Na+,K(+)-ATPase activity. In contrast, Na+,K(+)-ATPase activity measured in IMCD cell lysates was not altered. These results suggested that CP inhibited Na+,K(+)-ATPase activity in intact IMCD cells indirectly either by blocking Na+ entry or by inhibiting mitochondrial oxidative phosphorylation. Nystatin (Na+ ionophore) and carbonyl cyanide m-chlorophenylhydrazone (CCCP, uncoupler of oxidative phosphorylation) were used to distinguish between these possibilities. Nystatin-stimulated and CCCP-uncoupled QO2 were reduced in CP-treated IMCD cells by 34 +/- 10% and 25 +/- 5%, respectively, indicating mitochondrial injury. Again, the effects of CP on nystatin-stimulated and CCCP-uncoupled QO2 in IMCD cells were significantly less dramatic than in PT cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗