Biomedical subjects

A Garcia-Perez

Publications and source records attributed to A Garcia-Perez.

At least 19 recordsLinked to original sources

PubMed1997

Distinct regulation of osmoprotective genes in yeast and mammals. Aldose reductase osmotic response element is induced independent of p38 and stress-activated protein kinase/Jun N-terminal kinase in rabbit kidney cells.

In yeast glycerol-3-phosphate dehydrogenase 1 is essential for synthesis of the osmoprotectant glycerol and is osmotically regulated via the high osmolarity glycerol (HOG1) kinase pathway. Homologous protein kinases, p38, and stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK) are hyperosmotically activated in some mammalian cell lines and complement HOG1 in yeast. In the present study we asked whether p38 or SAPK/JNK signal synthesis of the osmoprotectant sorbitol in rabbit renal medullary cells (PAP-HT25), analogous to the glycerol system in yeast. Sorbitol synthesis is catalyzed by aldose reductase (AR). Hyperosmolality increases AR transcription through an osmotic response element (ORE) in the 5'-flanking region of the AR gene, resulting in elevated sorbitol. We tested if AR-ORE is targeted by p38 or SAPK/JNK pathways in PAP-HT25 cells. Hyperosmolality (adding 150 mM NaCl) strongly induces phosphorylation of p38 and of c-Jun, a specific target of SAPK/JNK. Transient lipofection of a dominant negative mutant of SAPK kinase, SEK1-AL, into PAP-HT25 cells specifically inhibits hyperosmotically induced c-Jun phosphorylation. Transient lipofection of a dominant negative p38 kinase mutant, MKK3-AL, into PAP-HT25 cells specifically suppresses hyperosmotic induction of p38 phosphorylation. We cotransfected either one of these mutants or their empty vector with an AR-ORE luciferase reporter construct and compared the hyperosmotically induced increase in luciferase activity with that in cells lipofected with only the AR-ORE luciferase construct. Hyperosmolality increased luciferase activity equally (5-7-fold) under all conditions. We conclude that hyperosmolality induces p38 and SAPK/JNK cascades in mammalian renal cells, analogous to inducing the HOG1 cascade in yeast. However, activation of p38 or SAPK/JNK pathways is not necessary for transcriptional regulation of AR through the ORE. This finding stands in contrast to the requirement for the HOG1 pathway for hyperosmotically induced activation of yeast GPD1.

Aldehyde Reductase↗

PubMed1994

Water channel vesicles from toad urinary bladder contain a family of proteins present in other tissues.

Antidiuretic hormone (ADH) stimulation causes the fusion and subsequent retrieval of cytoplasmic vesicles containing water channels (WCV) with the apical membrane of toad bladder granular cells. Previously, we showed that purified WCV contain 12 major protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. To identify various WCV proteins, we screened a panel of mouse monoclonal antibodies and characterized an immunoglobulin G1 monoclonal antibody, 5E5, that recognizes integral membrane WCV proteins of 38, 33, and 31 kDa. Immunocytochemistry and Western blot analyses show that 5E5 binds to multivesicular body endosomes shown previously to contain ADH water channels. In addition, 5E5 recognizes these proteins in selected cells of the skin, intestine, liver, kidney, spleen, and lung. However, 5E5 does not appear to recognize components of the water channel itself. We conclude that WCV contain several membrane proteins recognized by 5E5 that are present in certain cells of the other organs. Monoclonal 5E5 provides a probe to determine the structure and function of these endosomal proteins as well as their role in the ADH water permeability response.

Animals↗

PubMed1993

Localization of NaPi-1, a Na-Pi cotransporter, in rabbit kidney proximal tubules. I. mRNA localization by reverse transcription/polymerase chain reaction.

We have recently isolated from a rabbit cortex cDNA library a cDNA clone (NaPi-1), which, after in vitro transcription (cRNA) and injection into Xenopus laevis oocytes, expresses Na-dependent Pi uptake [Werner A, et al. (1991) Proc Natl Acad Sci USA 88:9608-9612]. The aim of the present work was to study the nephron location of the NaPi-1-related mRNA(s) by combining nephron microdissection procedures, reverse transcription (RT) and amplification of the resultant cDNA by the polymerase chain reaction (PCR). RT-PCR using NaPi-1-specific primers (different combinations) and either total kidney cortex RNA or microdissected proximal tubule segments resulted in two PCR products, both of approximately the expected length (but differing by about 30 base pairs). Restriction-enzyme analysis and nucleotide sequencing confirmed that both PCR products are related to NaPi-1 and that the "longer" PCR product has an insert of 26 base pairs containing an AluI restriction site. Nephron microdissection documents expression of NaPi-1-related mRNA(s) in superficial and deep proximal tubules (S1, S2 and S3 segments) and their absence in glomeruli, thin descending limb and thick ascending limbs of Henle's loop, distal convoluted tubules and cortical and inner medullary collecting ducts. These experiments suggest a "microheterogeneity" of NaPi-1-related mRNA(s) (which is not detected in Northern blot analysis) and proximal tubular expression of NaPi-1.

Animals↗

PubMed1993

Studies by competitive PCR of glomerulosclerosis in growth hormone transgenic mice.

We have shown that the glomerulosclerotic lesions of mice transgenic for bovine growth hormone (bGH mice) consisted of a change in the phenotype of glomerular collagens and an elevation of the mRNAs for these collagens in whole kidney. The purpose of this study was to determine whether these phenotypic and quantitative changes were present in the glomeruli. We used the increased sensitivity afforded by reverse transcription followed by the polymerase chain reaction (RT-PCR) to detect type I collagen mRNA and a quantitative PCR assay to quantitate type IV collagen mRNA in microdissected glomeruli. There was a six- to eightfold increase in alpha 1IV collagen mRNA in the glomeruli of bGh mice. alpha 1(I) collagen mRNA was present in glomeruli of bGH mice, which is consistent with our previous findings that the sclerotic mesangium contained type I collagen peptides by immunofluorescence microscopy. Normal glomeruli did not contain detectable amounts of alpha 1I collagen mRNA. In summary, we found a phenotypic change in glomeruli of mice transgenic for bGH consisting of increased type IV collagen mRNA levels and the appearance of type I collagen mRNA. Thus, the development of glomerulosclerosis appeared to be at least partially regulated at a pretranslational level.

Animals↗

PubMed1992

Cloning of the cDNa for a Na+/myo-inositol cotransporter, a hypertonicity stress protein.

Kidney medullary cells in situ, as well as kidney-derived Madin-Darby canine kidney (MDCK) cells accumulate nonperturbing, small organic solutes (osmolytes), including myo-inositol, when bathed in hypertonic media. Accumulation of osmolytes balances the osmolality of extracellular fluid without raising intracellular salts that would perturb cellular functions. In hypertonic media, increased myo-inositol accumulation is the result of increased activity of a Na+/myo-inositol cotransporter. We have isolated a cDNA encoding a Na+/myo-inositol cotransporter from MDCK cells using expression in Xenopus oocytes. The cDNA sequence predicts a protein of 718 amino acids with a significant amino acid sequence similarity to the Na+/D-glucose cotransporters of absorbing epithelia. Transporter mRNA is present in kidney and brain and is markedly induced in MDCK cells by medium hypertonicity, demonstrating that adaptation to hypertonic stress involves up-regulation of transporter mRNA accumulation.

Amino Acid Sequence↗

PubMed1992

Cloning of a Na(+)- and Cl(-)-dependent betaine transporter that is regulated by hypertonicity.

Many hypertonic bacteria, plants, marine animals, and the mammalian renal medulla are protected from the deleterious effects of high intracellular concentrations of electrolytes by accumulating high concentrations of the nonperturbing osmolyte betaine. When kidney-derived Madin-Darby canine kidney (MDCK) cells are cultured in hypertonic medium, they accumulate betaine to 1,000 times its medium concentration. This results from induction by hypertonicity of high rates of betaine transport into cells. We have isolated a cDNA (BGT-1) encoding a renal betaine transporter by screening an MDCK cell cDNA library for expression of a betaine transporter in Xenopus oocytes. The cDNA encodes a single protein of 614 amino acids, with an estimated molecular weight of 69 kDa. The deduced amino acid sequence exhibits highly significant sequence and topographic similarity to brain gamma-amino-n-butyric acid (GABA) and noradrenaline transporters, suggesting that the renal BGT-1 is a member of the brain GABA/noradrenaline transporter gene family. Expression in oocytes indicates that the BGT-1 protein has both betaine and GABA transport activities that are Cl(-)- as well as Na(+)-dependent and functionally similar to betaine and GABA transport in MDCK cells. Northern hybridization indicates that transporter mRNA is localized to the kidney medulla and is induced in MDCK cells by hypertonicity.

Amino Acid Sequence↗

PubMed1992

Kidney aldose reductase gene transcription is osmotically regulated.

Cells generally adapt to long-term hypertonic stress by accumulating organic osmolytes. PAP-HT25 renal medullary cells in hypertonic medium accumulate sorbitol through a reaction catalyzed by aldose reductase and betaine through osmotically regulated transport. Hypertonicity increases aldose reductase protein synthesis rate by elevating its mRNA abundance. To test whether the rise in aldose reductase mRNA is due to enhanced transcription, PAP-HT25 cells adapted to isotonic medium were switched to hypertonic medium, and transcription rate was measured by nuclear run-on. Aldose reductase transcription rate peaked at 17-fold the isotonic level after 12 h of hypertonicity. Then, transcription fell as sorbitol and betaine accumulated. Transcription stabilized at fivefold the isotonic level within days. Aldose reductase mRNA stability was not significantly different between the hypertonic and isotonic steady states. Thus aldose reductase mRNA is osmotically regulated through changes in its transcription. The osmotically induced rise in aldose reductase transcription is blunted by the accumulation of intracellular betaine and is exaggerated and prolonged by preventing the accumulation of both sorbitol (by aldose reductase inhibition) and betaine (by removal from the medium). This study presents the first description of osmoregulated gene transcription in animal cells.

Aldehyde Reductase↗

PubMed1992

Time course of renal glutamate dehydrogenase induction during NH4Cl loading in rats.

To study mechanisms involved in renal glutamate dehydrogenase (GDH) regulation in response to systemic acid loading, we have measured blood pH, ammonium excretion, renal GDH mRNA levels, and GDH activity in rats. Acid intake (0.28 M NH4Cl in drinking water for 3 days) increased GDH mRNA levels in the renal cortex, but had no effect in the outer stripe of the outer medulla, inner stripe of the outer medulla, or the inner medulla. Rats were subjected to a step change in acid intake by alkali loading for 3 days (7.2 meq NaHCO3 per day in food slurry) and shifting to acid loading for up to 7 days (7.2 meq NH4Cl in food slurry). Ammonium excretion rose rapidly, increasing by 14-fold in the first 24-h period and 38-fold in the second 24-h period. Cortical GDH mRNA levels were increased relative to alkali-loaded values by 3.7-fold in 24 h, 4.3-fold in 4 days, but only 2.2-fold in 7 days. GDH activity was unchanged after 24 h of acid intake, but was significantly increased after 48 h. We concluded the following: 1) GDH mRNA is present in all regions of the kidney, but levels increase in response to acid loading only in the renal cortex; 2) GDH mRNA levels increase within 1 day after the initiation of acid loading, but the associated increase in functional enzyme activity takes 2 or more days; and 3) the large increases in ammonium excretion that occur in the first day after initiation of acid loading are not dependent on increased GDH activity.

Ammonium Chloride↗

PubMed1992

Age-related changes in alpha 1- and alpha 2-chain type IV collagen mRNAs in adult mouse glomeruli: competitive PCR.

Studies of age-related changes in glomerular extracellular matrix (ECM) synthesis in normal mice have been hampered by the difficulty of isolating sufficient numbers of intact glomeruli and by the inability to quantify different mRNA species. The purpose of this study was to identify and quantitate the individual mRNAs coding for alpha 1- and alpha 2-chains of type IV collagen in isolated, single glomeruli of normal mice at different ages. These data on normal ECM synthesis were necessary for the understanding of glomerulosclerosis, a condition characterized by excess deposition of collagen. Pools of freshly microdissected adult mouse glomeruli were reverse transcribed in situ, and alpha 1-IV and alpha 2-IV collagen mRNAs were individually amplified by means of specific primers and the polymerase chain reaction (PCR), according to a previously published method. A competitive PCR assay, based on utilization of mutated cDNAs, allowed the reproducible, quantitative, and separate determination of the absolute amounts of both alpha 1-IV and alpha 2-IV mRNAs measured, as their respective cDNAs, in one-tenth of one glomerulus. The levels of alpha 1-IV and alpha 2-IV collagen mRNA were 208 +/- 36.0 x 10(-4) and 161.2 +/- 18.6 x 10(-4) amol/glomerulus in 5-wk-old mice. There were no significant age-related differences at 8, 12, and 24 wk. The mean levels over this period were 60.2 +/- 4.9 x 10(-4) for alpha 1-IV collagen mRNA and 63.9 +/- 5.8 x 10(-4) amol/glomerulus for alpha 2-IV collagen mRNA. Two of three 24-wk-old mice had mild glomerulosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1992

Maturation of aldose reductase expression in the neonatal rat inner medulla.

Newborns are less able to concentrate urine than adults are. With development of the concentrating system and a hypertonic medullary interstitium, there is a need to generate intracellular osmolytes such as sorbitol, which is produced in a reaction catalyzed by the enzyme aldose reductase. We sought to discriminate between two possible mechanisms of aldose reductase induction during development: (a) a response to an osmotic stimulus generated by the concentrating mechanism; or (b) part of the genetic program for development of the kidney. We measured the change in aldose reductase mRNA and activity in terminal inner medullary collecting ducts (IMCDs) microdissected from Sprague-Dawley rats during the first month of life. Aldose reductase mRNA was assayed by Northern analysis of total RNA from inner medulla and by detection of the reverse transcription-polymerase chain reaction (RT-PCR) product obtained from single IMCDs using aldose reductase-specific primers. Aldose reductase activity was measured in IMCDs taken from the same rats using a fluorescent microassay. Newborn rat IMCDs had minimal aldose reductase mRNA or activity, however mRNA was readily detected in IMCDs from rats older than 3 d of age, with peak expression occurring at 1-3 wk of age before decreasing to adult levels. In contrast, the mRNA level for a housekeeping metabolic enzyme, malate dehydrogenase, did not change during maturation. Aldose reductase enzyme activity was readily detectable by 6 d of age, peaked at 20 d, then decreased to adult levels. Urine osmolality remained < 600 mosmol/kg until 16 d, then increased to > 1,100 mosmol/kg after 20 d. Thus, aldose reductase mRNA and activity increased before urinary osmolality reached 870 mosmol/kg. Because urine osmolality may not be indicative of inner medullary osmolality and because mother's milk may provide excessive free water to the pups under 3 wk of age, half of the animals in several litters were separated from their mothers for 1 d and inner medullary osmolality, in addition to urine osmolality, was measured by vapor pressure osmometry, while aldose reductase mRNA was assessed densitometrically in IMCDs after RT-PCR. Although fluid restriction resulted in a near doubling of urine osmolality and a tendency towards increased aldose reductase mRNA, there was no consistently significant increase in aldose reductase mRNA or inner medullary osmolality during the first 13 d of life compared to the suckling animals. On the other hand, 2-3-wk-old rats showed significant increases in aldose reductase mRNA, accompanied by increases in inner medullary osmolality, after fluid restriction. Thus, the dissociation between the increases in aldose reductase expression and inner medullary hyperosmolality indicates that the maturational induction of the aldose reductase gene is not a consequence of osmotic stimulation, but rather, part of the developmental program of the kidney.

Aldehyde Reductase↗

PubMed1992

How tonicity regulates gene expression.

The expression of a number of different mammalian genes is directly affected by hypertonicity. At present, the list of their products includes aldose reductase, heat shock proteins, early response factors, and transporters for betaine, inositol, and taurine. Hypertonicity increases the abundance of the mRNAs for all of them. Aldose reductase mRNA levels increase because of increased transcription with little change in the stability of its mRNA. Transcription of the betaine transporter also increases. The mechanisms by which hypertonicity increases the transcription of these mammalian genes remain speculative. However, the consideration of transcriptional control of betaine transport in bacteria and of heat shock proteins in many organisms provides interesting insight into this question.

Aldehyde Reductase↗

PubMed1991

Accumulation of glycerophosphocholine (GPC) by renal cells: osmotic regulation of GPC:choline phosphodiesterase.

Although GPC has long been recognized as a degradation product of phosphatidylcholine, only recently is there wide appreciation of its role as a compatible and counteracting osmolyte that protects cells from osmotic stress. GPC is osmotically regulated in renal cells. Its level varies directly with extracellular osmolality. Cells in the kidney medulla in vivo and in renal epithelial cell cultures (MDCK) accumulate large amounts of GPC when exposed to high concentrations of NaCl and urea. Osmotic regulation of GPC requires choline in the medium, presumably as a precursor for synthesis of GPC. Choline transport into the cells, however, is not osmoregulated. The purpose of the present studies was to use MDCK cell cultures as a defined model to distinguish whether osmotically induced accumulation of GPC results from increased GPC synthesis or decreased GPC disappearance. The rate of incorporation of 14C from [14C]choline into GPC, the steady-state GPC synthesis rate, and the activity of phospholipase A2 (which can catalyze a step in the synthesis of GPC from phosphatidylcholine) are not increased by high NaCl and urea. In fact all are decreased by approximately one-third. Therefore, we find no evidence that high NaCl and urea increases the GPC synthesis rate. On the other hand, the rate coefficient for cellular GPC disappearance and the activity of GPC:choline phosphodiesterase (EC 3.1.4.2), which catalyzes degradation of GPC, are decreased by approximately two-thirds by high NaCl and urea. We conclude that high NaCl and urea increase the level of GPC by inhibiting its enzymatic degradation.

Animals↗

PubMed1991

Induction of glycinebetaine uptake into Xenopus oocytes by injection of poly(A)+ RNA from renal cells exposed to high extracellular NaCl.

Madin-Darby canine kidney (MDCK) cells accumulate glycinebetaine via Na(+)-dependent transport in response to hypertonic stress. When extracellular tonicity is increased by the addition of NaCl, Vmax for glycinebetaine transport increases without an associated change in Km, consistent with an increase in the number of functioning transporters. To test whether increased transport activity results from increased gene expression, we injected poly(A)+ RNA (mRNA) from MDCK cells into Xenopus oocytes and assayed for glycinebetaine uptake in ovo. RNA-induced Na(+)-dependent uptake is observed in oocytes injected with mRNA from cells exposed to high extracellular NaCl, but not in oocytes injected with either water or mRNA from cells maintained in isotonic medium. Unfractionated mRNA induces glycinebetaine uptake in ovo at a rate which is approximately 3-fold higher than in water-injected controls. Size-fractionated mRNA (median size 2.8 kilobases) induces uptake at a rate which is approximately 7-fold higher than controls. Such RNA-induced transport activity in ovo is consistent with heterologous expression of Na(+)/glucinebetaine cotransporters encoded by renal mRNA. Increased transporter mRNA in cells exposed to hypertonicity probably underlies the pattern of expression observed in ovo. This can account for the observed rise in MDCK cell glycinebetaine transport during hypertonic stress.

Animals↗

PubMed1991

Role of organic osmolytes in adaptation of renal cells to high osmolality.

Kidney cells accumulate organic osmolytes in order to protect themselves from the high concentrations of NaCl and urea in the blood and interstitial fluid of the renal medulla. The renal medullary organic osmolytes are sorbitol, inositol, betaine and GPC. The concentrations of these solutes in renal medullary NaCl and urea concentration, as summarized in Fig. 8 (the putative controlled steps are highlighted). Sorbitol accumulates by synthesis from glucose, catalyzed by aldose reductase. Hypertonicity increases the transcription of the gene that encodes this enzyme. GPC is synthesized from choline, and the amount retained apparently may be controlled by the activity of GPC diesterase, an enzyme that catabolizes GPC. Inositol and betaine are taken up from the medium by sodium-dependent transport, and this transport is increased by hypertonicity. Control of these processes is slow (hours to days), but a decrease in tonicity causes a transient, rapid efflux of the solutes, which prevents the cells from becoming overly distended. Similar strategies are used by all types of cells, including bacteria and those in plants and animals, that can adapt to hyperosmotic stress.

Aldehyde Reductase↗

PubMed1991

Renal Na-myo-inositol cotransporter mRNA expression in Xenopus oocytes: regulation by hypertonicity.

Canine renal cells in culture (MDCK cells) accumulate organic osmolytes, including myo-inositol (MI), in response to hypertonic stress. When medium tonicity is increased, intracellular concentration of MI rises because hypertonicity elicits increased uptake of MI via Na-MI cotransporter(s). To study the mechanism for this increase in cotransporter activity, poly(A)+ RNA isolated from MDCK cells maintained in hypertonic or isotonic medium was injected into Xenopus oocytes, and Na-dependent MI uptake was measured 3-5 days later. Poly(A)+ RNA from hypertonic cells induced clear expression of the cotransporter. In contrast, oocytes injected with poly(A)+ RNA isolated from MDCK cells maintained in isotonic medium exhibited cotransporter activity like oocytes injected with water. Upon size fractionation of RNA, peak activity appeared in a fraction that contained poly(A)+ RNA with median size of approximately 4 kilobases. Na-dependent MI uptake by poly(A)+ RNA-injected oocytes was inhibited by both phlorizin and phloretin. We suggest that hypertonicity-induced upregulation of the Na-MI cotransporter involves an increase in mRNA and synthesis of cotransporter protein(s).

Animals↗

PubMed1991

Intracellular betaine substitutes for sorbitol in protecting renal medullary cells from hypertonicity.

Renal medullary cells are normally exposed to a variably high extracellular NaCl concentration. They compensate by accumulating large amounts of organic osmolytes, including sorbitol and betaine. The sorbitol is synthesized from glucose, catalyzed by aldose reductase. Previously, inhibition of aldose reductase activity was noted to greatly reduce renal medullary cell survival and growth (measured by cloning efficiency) in tissue cultures of renal medullary cells in hypertonic medium. In contrast, inhibition of aldose reductase and renal medullary sorbitol accumulation is not associated with kidney damage in vivo. In the present experiments we find that addition of betaine to the medium, and its resultant uptake by the cells, largely replaces the decrease in sorbitol caused by aldose reductase inhibitors and restores the cloning efficiency. We presume that in vivo uptake of betaine by renal medullary cells similarly protects them from harm when aldose reductase inhibitors lower sorbitol. The results also demonstrate that one organic osmolyte can substitute for another in protecting cells from hypertonicity, consistent with the compatible osmolytes hypothesis.

Aldehyde Reductase↗

PubMed1991

RT-PCR microlocalization of mRNA for guanylyl cyclase-coupled ANF receptor in rat kidney.

Microlocalization of mRNA coding for the guanylyl cyclase-coupled atrial natriuretic factor (ANF) receptor was carried out in the rat kidney. We used a combination of reverse transcription and polymerase chain reaction (RT-PCR) in individual microdissected renal tubule segments, glomeruli, and vasa recta bundles. Relative quantitation of the resulting amplified cDNA utilized densitometry of autoradiograms from Southern blots probed with a specific 32P-labeled probe. Among renal tubule segments, the largest signal was found in the terminal inner medullary collecting duct (IMCD). Slightly smaller signals were found in the initial IMCD and in loop of Henle segments from the inner medulla. Readily detectable signals were also seen in the following segments (in descending order): cortical collecting duct, proximal convoluted tubule, medullary thick ascending limb, cortical thick ascending limb, distal convoluted tubule, and outer medullary collecting duct. Large signals were also detected in glomeruli and in vasa recta bundles from the inner stripe of the outer medulla. Based on these results, we conclude that 1) renal microlocalization of specific mRNAs coding for hormone receptors is feasible through application of the RT-PCR procedure in microdissected renal tubules and vascular elements, and 2) the gene for the guanylyl cyclase-coupled ANF receptor is broadly expressed along the nephron, raising the possibility that multiple sites of ANF action are present.

Animals↗

PubMed1991

Renal medullary organic osmolytes.

Sorbitol, inositol, GPC, and betaine are the predominant organic osmolytes in renal medullary cells. They protect the cells from harmful effects of the high interstitial NaCl and urea concentrations that occur normally in the renal medulla with operation of the urinary concentrating mechanism. Their levels correlate with extracellular NaCl concentration and, in the case of GPC, also with urea. Sorbitol is synthesized from glucose in a reaction catalyzed by aldose reductase. Inositol and betaine are transported into the cell. Glycerophosphorylcholine synthesis is dependent on choline. The transcription of aldose reductase and the transport of betaine and inositol are regulated, dependent on the degree of hypertonicity. Normal organic osmolyte regulation contributes to the survival and growth of medullary cells in their hyperosmolal environment, and defective regulation can damage them.

Animals↗