Glycocalyx heterogeneity of rat kidney urinary tubule: demonstration with a lectin-gold technique specific for sialic acid

The distribution of sialic acid residues in rat kidney urinary tubule was investigated by light and electron microscopy with a lectin-gold technique. The application of the sialic acid specific Limax flavus lectin resulted in intense plasma membrane labeling of the epithelium of the entire proximal tubule and thin limbs of loop of Henle. In contrast, the plasma membrane of the epithelium lining the medullary portion of the thick ascending limb of Henle was not labeled. In the cortical portion, however, microvilli-bearing positive and smooth-surfaced negative cells were present. Moreover, all cells of the convoluted distal tubules were labeled along their plasma membrane. These data demonstrate the existence of a gross difference in glycocalyx composition between proximal tubules and thin limbs of loop of Henle on one hand and thick ascending limbs on the other. In addition, fine heterogeneity in glycocalyx composition between medullary and cortical portion of thick ascending limb exists. It is concluded that the differences in sialic acid content of the glycocalyx may be related to the functional diversity exhibited by these tubular regions.     

Carbonic anhydrase activity in kidney and lower intestine of the European starling

A histochemical investigation of kidney and lower intestine of the European starling (Sturnus vulgaris) shows no carbonic anhydrase activity in proximal convoluted tubules, although activity is seen in similarly prepared sections of rat proximal tubules. Early distal tubule cells in the starling are stained throughout the cytoplasm and at the apical and highly infolded basolateral membranes. Late distal tubules lose apical activity and have reduced basolateral infolding, resulting in less intense staining. Darkly stained intercalated cells appear in the connecting tubules and cortical collecting ducts. Both of these segments also show intense basolateral staining. Medullary cones of the starling are highly organized, with central zones containing unstained thin descending limbs of loops of Henle, surrounded by both medullary collecting ducts with only scattered cells staining for enzyme, and by thick ascending limb segments. The latter contain many uniformly stained cells intermingled with occasional unstained cells. Scattered cells of the starling colonic villi demonstrate intense apical brush border membrane staining as well as cytoplasmic staining. Cells lining the cloaca stain less intensely. A biochemical assay for carbonic anhydrase was used to quantify enzyme activity in these tissues. Starling kidney contained 1.96 ± 0.33 (mean ± SEM) enzyme units/mg protein, less than half the activity seen in rat kidney. Stripped colonic epithelium contained 0.66 ± 0.15 enzyme units/mg protein. These quantitative results correlate well with the interpretations derived from the histochemical observations. The lack of proximal tubule carbonic anhydrase activity suggests that the avian kidney relies more on distal nephron segments to achieve net acidification of the urine.     

Immunocytochemical localization of Na+, K+-ATPase in the rat kidney

To determine if rat kidney Na+, K+-ATPase can be localized by immunoperoxidase staining after fixation and embedding, we prepared rabbit antiserum to purified lamb kidney medulla Na+, K+-ATPase. When sodium dodecylsulfate polyacrylamide electrophoretic gels of purified lamb kidney Na+, K+-ATPase and rat kidney microsomes were treated with antiserum (1:200), followed by [125I]-Protein A and autoradiography, the rat kidney microsomes showed a prominent radioactive band coincident with the alpha-subunit of the purified lamb kidney enzyme and a fainter radioactive band which corresponded to the beta-subunit. When the Na+, K+-ATPase antiserum was used for immunoperoxidase staining of paraffin and plastic sections of rat kidney fixed with Bouin's, glutaraldehyde, or paraformaldehyde, intense immunoreactive staining was present in the distal convoluted tubules, subcapsular collecting tubules, thick ascending limb of the loops of Henle, and papillary collecting ducts. Proximal convoluted tubules stained faintly, and the thin portions of the loops of Henle, straight descending portions of proximal tubules, and outer medullary collecting ducts did not stain. Staining was confined to basolateral surfaces of tubular epithelial cells. No staining was obtained with preimmune serum or primary antiserum absorbed with purified lamb kidney Na+, K+-ATPase, or with osmium tetroxide postfixation. We conclude that the basolateral membranes of the distal convoluted tubules and ascending thick limb of the loops of Henle are the major sites of immunoreactive Na+, K+-ATPase concentration in the rat kidney.     

Specialized expression of simple O-glycans along the rat kidney nephron.

Glycosyltransferases can exhibit tissue-specific expression. By histochemistry glycosyltransferases and their products can be localized to specific cell types in organs of complex cellular composition. We have applied the lectin Amaranthin, having a nominal specificity for Galbeta1,3GalNAcR and Neu5Ac2,3Galbeta1, 3GalNAcalpha-R, and a monoclonal antibody raised against Galbeta1, 3GalNAcalphaR to examine the distribution of these simple O-glycans in adult rat kidney. The monoclonal antibody stained ascending thin limbs of Henle, distal convoluted tubules, and collecting ducts of cortex and outer medulla. Remarkably, the ascending thick limb of Henle, located between ascending thin limb and distal convoluted tubules, was unreactive. However, Amaranthin staining was detectable in ascending thick limbs of Henle, in addition to the structures positive with the monoclonal antibody. In kidney extracts, two bands of approximately 160 kDa and >210 kDa were reactive with both Amaranthin and the monoclonal antibody. One band at approximately 200 kDa, and a smear at approximately 100 kDa, were reactive only with Amaranthin. Our data show that in rat kidney simple O-linked glycans are expressed in a highly specialized manner along the renal tubule and can be detected only on a few glycoproteins. This may reflect a cell-type-specific expression of the corresponding glycosyltransferases.     

Expression of the membrane-associated carbonic anhydrase isozyme XII in the human kidney and renal tumors.

Carbonic anhydrase isozyme XII (CA XII) is a novel membrane-associated protein with a potential role in von Hippel-Lindau carcinogenesis. Although Northern blotting has revealed positive signal for CA XII in normal human kidney, this is the first study to demonstrate its cellular and subcellular localization along the human nephron and collecting duct. Immunohistochemistry with a polyclonal antibody (PAb) raised against truncated CA XII revealed distinct staining in the basolateral plasma membrane of the epithelial cells in the thick ascending limb of Henle and distal convoluted tubules, and in the principal cells of the collecting ducts. A weak basolateral signal was also detected in the epithelium of the proximal convoluted tubules. In addition to the normal kidney specimens, this immunohistochemical study included 31 renal tumors. CA XII showed moderate or strong plasma membrane-associated expression in most oncocytomas and clear-cell carcinomas. The segmental, cellular, and subcellular distribution of CA XII along the human nephron and collecting duct suggests that it may be one of the key enzymes involved in normal renal physiology, particularly in the regulation of water homeostasis. High expression of CA XII in some renal carcinomas may contribute to its role in von Hippel-Lindau carcinogenesis.     

Carbonic anhydrase in the monkey kidney

The distribution of carbonic anhydrase in the kidney of the cynomolgus monkey was studied by the histochemical method of Hansson. Glomeruli and Bowman's capsule were inactive. Convoluted proximal tubules showed high enzyme activity at the brush border and the basolateral membranes and the cytoplasm. Straight proximal tubules were less intensely stained. In nephrons with long loops of Henle, the descending thin limb contained weak enzyme activity, whereas the ascending thin limb was inactive. The thick limb of Henle's loop displayed most enzyme activity at the luminal cell border. In distal convoluted tubules enzyme activity was restricted to the basal part of the cells. In the late distal tubule, intercalated cells appeared among the "ordinary" distal cells and contained abundant cytoplasmic enzyme. Many intensely stained intercalated cells were also found in the cortical and outer medullary segments of the collecting duct, intermingled with more weakly stained chief cells. In the inner medullary segment of the collecting duct, enzyme activity gradually disappeared. Many capillaries were clearly stained for enzyme activity. The capillary staining apparently varied with that of the kidney tubules; virtually all capillaries in the cortex, but very few in the inner medulla, were stained. The distribution of carbonic anhydrase in the kidney tubules of the monkey is very similar to that in man and in the rat, but the primate kidney differs from the rat kidney by the presence of capillary enzyme activity. The functional importance of this difference is not clear at present.     

Distribution of prostaglandin E2-sensitive adenylate cyclase along the rat nephron

To define sites of prostaglandin action of renal tubules, the distribution of adenylate cyclase sensitive to prostaglandin E₂ (PGE₂) was examined in single nephron segments dissected from rat kidney. Further, the interaction between PGE₂ and vasopressin on adenylate cyclase activity in nephron segments sensitive to vasopressin was evaluated. Procedures involved in isolating nephron segments were without effects on adenylate cyclase stimulation by PGE₂. PGE₂ stimulated adenylate cyclase activity of the thin descending limb of Henle (tDL), cortical collecting tubules (CCT), and medullary collecting tubules (MCT) at concentrations of 1.4 × 10^?5 to 2.8 × 10^?5 M. PGE₂ was without effects in other nephron segments tested including proximal convoluated tubules, proximal pars recta, the thin and thick ascending limb of Henle's loop, and distal and connecting tubules. PGE₂, at both high (2.8 × 10^?5 M) and low (2.8 × 10^?8 M) concentrations, did not inhibit adenylate cyclase activity stimulated by submaximal doses of vasopressin in medullary thick ascending limb of Henle (MTAL), CCT, and MCT. These data define the distribution of PGE₂-sensitive adenylate cyclase in the rat nephron, i.e., tDL, CCT, and MCT, and show the lack of direct inhibitory actions of PGE₂ on vasopressin sensitive adenylate cyclase in MTAL, CCT, and MCT.     

Stem cell marker TRA-1-60 is expressed in foetal and adult kidney and upregulated in tubulo-interstitial disease

The kidney has an intrinsic ability to repair itself when injured. Epithelial cells of distal tubules may participate in regeneration. Stem cell marker, TRA-1-60 is linked to pluripotency in human embryonic stem cells and is lost upon differentiation. TRA-1-60 expression was mapped and quantified in serial sections of human foetal, adult and diseased kidneys. In 8- to 10-week human foetal kidney, the epitope was abundantly expressed on ureteric bud and structures derived therefrom including collecting duct epithelium. In adult kidney inner medulla/papilla, comparisons with reactivity to epithelial membrane antigen, aquaporin-2 and Tamm–Horsfall protein, confirmed extensive expression of TRA-1-60 in cells lining collecting ducts and thin limb of the loop of Henle, which may be significant since the papillae were proposed to harbour slow cycling cells involved in kidney homeostasis and repair. In the outer medulla and cortex there was rare, sporadic expression in tubular cells of the collecting ducts and nephron, with positive cells confined to the thin limb and thick ascending limb and distal convoluted tubules. Remarkably, in cortex displaying tubulo-interstitial injury, there was a dramatic increase in number of TRA-1-60 expressing individual cells and in small groups of cells in distal tubules. Dual staining showed that TRA-1-60 positive cells co-expressed Pax-2 and Ki-67, markers of tubular regeneration. Given the localization in foetal kidney and the distribution patterns in adults, it is tempting to speculate that TRA-1-60 may identify a population of cells contributing to repair of distal tubules in adult kidney.     

Protein expression and gene mutation status of KIT and PDGFRA in renal cell carcinoma

The author investigated protein expression and gene mutations of KIT and PDGFRA in 61 consecutive surgical cases of renal cell carcinoma (RCC). The cases of RCC consisted of 43 clear cell RCC (CCRCC), 9 chromophobe RCC (ChrRCC), or 9 papillary RCC (PaRCC). Normal distribution of KIT and PDGFRA protein was also examined in non-tumorous normal parenchyma (n=10). In normal kidneys, KIT was expressed in distal convoluted tubules and collecting ducts, and PDGFRA in distal and proximal convoluted tubules and collecting ducts. KIT expression was recognized in 9 ChrRCC (100%, 9/9), but not in 43 CCRCC (0%, 0/43) and 9 PaRCC (0%, 0/9). PDGFRA expression was recognized in 7 CCRCC (16%, 7/43) and 2 PaRCC (28%, 2/9), but not in ChrRCC (0%, 0/9). A molecular genetic analysis using PCR-direct sequencing was performed in selected 30 cases (ChrRCC=9, CCRCC=12, PaRCC=9): it revealed no mutations in KIT (exons 9, 11, 13, and 17) or PDGFRA (exons 12 and 18) genes in any cases examined. These results suggest that in normal renal parenchyma KIT is expressed in distal convoluted tubules and collecting ducts, and PDGFRA in proximal and distal convoluted tubules and collecting ducts, that KIT is expressed exclusively in ChrRCC and its incidence is 100%, that KIT-positive ChrRCC was negative for PDGFRA, that PDGFRA is expressed in a small percentage in CCRCC and PaRCC, and that mutations of KIT (exons 9, 11, 13, and 17) and PDGFRA (exons 12 and 18) are absent in RCC.     

Histochemical localization of enzyme activity in the kidneys of male marmosets (Callithrix jacchus and Callithrix penicillata).

The distribution of several hydrolases and oxidoreductases was studied in the renal parenchyma of adult male marmosets (Callithrix jacchus and Callithrix penicillata). The oxidative enzymes showed a high reactivity in the proximal and distal tubules, whereas the hydrolases reacted strongly in the proximal tubules but only weakly or not at all in the thick limb of Henle's loop, distal tubules and collecting ducts. The NAD-dependent enzymes (except alpha-GPDH) showed a stronger reactivity in the proximal tubules, while the NADP-dependent ones were more reactive in the thick limb of Henle's loop and distal convoluted tubules. Two groups of interstitial cells were found in the medulla. A first group inside the outer medulla, showing cells rich in acid phosphatase and nonspecific esterases and a second group, close to the papilla, reactive to a certain number of oxidative enzymes. A different reactivity in cells of the distal convoluted tubules, thick limb of Henle's loops and collecting ducts (dark cells) was seen in the case of some enzymes like nonspecific esterase, alpha-GPDH and SDH.     

Localization by immunofluorescence and by light- and electron-microscopic immunoperoxidase techniques of Tamm–Horsfall glycoprotein in adult hamster kidney

1. Tamm-Horsfall glycoprotein was isolated from hamster urine and antiserum against it was produced in rabbits. Immunoglobulin G was isolated from the antiserum. 2. Indirect methods of immunofluorescence staining were applied to kidney sections previously fixed by both perfusion and immersion methods. Tamm-Horsfall glycoprotein was identified associated with only the cells of the ascending limb of the loop of Henle and the distal convoluted tubule. Maculae densae were free of the glycoprotein. 3. Indirect immunoperoxidase procedures with light microscopy were applied to kidney sections. The results extended those found by immunofluorescence by showing that the glycoprotein is largely associated with the plasma membrane of the cells. Macula densa cells were shown to be free of the glycoprotein, although the luminal surface of the remaining cells in the transverse section of the nephron at that region was shown to contain it. 4. A variety of immuno-electron-microscopic techniques were applied to sections previously fixed in a number of ways. Providing periodate/lysine/paraformaldehyde was used as the fixative, the glycoprotein was often seen to be present not only on the luminal surface of the cells of the thick ascending limb of the loop of Henle and of the distal convoluted tubule, but also on the basal plasma membrane, including the infoldings. 5. It is generally accepted that the hyperosmolarity in the medulla of the kidney results from passage of Cl(-) ions with their accompanying Na(+) ions across the single cell layer of the lumen of the thick ascending limb of the loop of Henle, a region of the nephron with relatively high impermeability to water. We suggest that Tamm-Horsfall glycoprotein operates as a barrier to decrease the passage of water molecules by trapping the latter at the membrane of the cells. Our hypothesis requires the glycoprotein on the basal plasma membrane also.     

CHIP28 water channels are localized in constitutively water-permeable segments of the nephron

The sites of water transport along the nephron are well characterized, but the molecular basis of renal water transport remains poorly understood. CHIP28 is a 28-kD integral protein which was proposed to mediate transmembrane water movement in red cells and kidney (Preston, G. M., T. P. Carroll, W. B. Guggino, and P. Agre. 1992. Science [Wash. DC]. 256:385-387). To determine whether CHIP28 could account for renal epithelial water transport, we used specific polyclonal antibodies to quantitate and localize CHIP28 at cellular and subcellular levels in rat kidney using light and electron microscopy. CHIP28 comprised 3.8% of isolated proximal tubule brush border protein. Except for the first few cells of the S1 segment, CHIP28 was immunolocalized throughout the convoluted and straight proximal tubules where it was observed in the microvilli of the apical brush border and in basolateral membranes. Very little CHIP28 was detected in endocytic vesicles or other intracellular structures in proximal tubules. Uninterrupted, heavy immunostaining of CHIP28 was also observed over both apical and basolateral membranes of descending thin limbs, including both short and long loops of Henle. These nephron sites have constitutively high osmotic water permeabilities. CHIP28 was not detected in ascending thin limbs, thick ascending limbs, or distal tubules, which are highly impermeable to water. Moreover, CHIP28 was not detected in collecting duct epithelia, where water permeability is regulated by antidiuretic hormone. These determinations of abundance and structural organization provide evidence that the CHIP28 water channel is the predominant pathway for constitutive transepithelial water transport in the proximal tubule and descending limb of Henle's loop.     

Histochemical demonstration of l-amino acid-tetrazolium reductase

Summary A method for the histochemical demonstration of l-amino acid-tetrazolium reductase is described. The diformazan deposition was obtained with l-leucine as substrate and no precipitate was present when l-serine and l-lisine were used. In the kidney the reaction was positive in the podocytes, the cells of proximal and distal convoluted tubules, in the ascending limbs of Henle and in the cells of the collecting tubules. In the liver the reaction was positive in the cytoplasm of the hepatocytes. The reaction pattern suggests that it is predominantly extramitochondrial. The specificity of this method is discussed.     

Protein p0071, an armadillo plaque protein of adherens junctions, is predominantly expressed in distal renal tubules

Protein p0071 is a member of the p120-subfamily of armadillo proteins and is well known as a junctional plaque component involved in cell–cell adhesion, especially in adherens junctions. By systematic immunohistochemical analysis of mouse and human kidney tissues, p0071 was prominently detected in distinct kidney tubules. Upon double-labeling immunolocalization experiments with segment-specific markers, p0071 was predominantly localized in distal straight and convoluted tubules and to a lesser extent in proximal tubules, in the ascending thin limb of loop of Henle and in the collecting ducts. In capillaries of the kidney, p0071 co-localized with VE-cadherin an endothelium-specific cadherin. Protein p0071 was also detected in both, renal cell carcinomas derived from distal tubules and in maturing nephrons of early mouse developmental stages. Immunoblotting of total extracts of cultured cells of renal origin showed that p0071 was detected in all human and murine cells analyzed. Upon immunolocalization, p0071 was observed in adherens junctions but also in distinct cytoplasmic structures at the cell periphery of cultured cells. Possible structural and functional roles of p0071 are suggested by its preferential occurrence in distinct tubule segments, and its potential use as a cytodiagnostic cell type marker in renal pathology is discussed.     

Immunoexpression of aquaporins 1, 2, 3 and 4 in kidney of yak (Bos grunniens) on the Qinghai-Tibetan Plateau

Aquaporins (AQP) 1, 2, 3 and 4 belong to the aquaporin water channel family and play an important role in urine concentration by reabsorption of water from renal tubule fluid. Renal AQPs have not been reported in the yak (Bos grunniens), which resides in the Qinghai Tibetan Plateau. We investigated AQPs 1?4 expressions in the kidneys of Yak using immunohistochemical staining. AQP1 was expressed mainly in the basolateral and apical membranes of the proximal tubules and descending thin limb of the loop of Henle. AQP2 was detected in the apical plasma membranes of collecting ducts and distal convoluted tubules. AQP3 was located in the proximal tubule, distal tubule and collecting ducts. AQP4 was located in the collecting ducts, distal straight tubule, glomerular capillaries and peritubular capillaries. The expression pattern of AQPs 1?4 in kidney of yak was different from other species, which possibly is related to kidney function in a high altitude environment.     

Mechanism of release of urinary Tamm-Horsfall glycoprotein from the kidney GPI-anchored counterpart

Human Tamm-Horsfall glycoprotein (THP) is synthesised in the thick ascending limb of Henle and convoluted distal tubules, inserted into luminal cell-surface by the glycosyl-phosphatidylinositol (GPI)-anchor and excreted in urine at a rate of 50-100 mg per day. Up to date there is no indication on the way in which THP is excreted into the urinary fluid. In this study, we examined by Western blotting THP from human kidney in comparison to urinary THP. As expected for a GPI-anchored protein, THP was recovered from the kidney lysate in a Triton X-100 insoluble form, which moved in a sucrose gradient to a zone of low density. The apparent molecular weight of kidney THP appeared greater than that of urinary THP, but no difference in the electrophoretic mobility was observed when the former was subjected to GPI-specific phospholipase-C treatment, strongly suggesting that a proteolytic cleavage at the juxtamembrane-ectodomain of kidney THP is responsible for the urinary excretion.     

Sites of urokinase-type plasminogen activator expression and distribution of its receptor in the normal human kidney

The urokinase-type plasminogen activator (uPA) is secreted into the urine at high concentrations and both the uPA protein and mRNA are present in human renal tissue. Normal kidney tissue also expresses the receptor for uPA. Neither the precise sites of uPA mRNA expression, nor the distribution of the uPA-receptor antigen, have been elucidated in the human kidney. In the present study, the sites of uPA mRNA expression were identified by in situ hybridization, and the cellular localization of both uPA and uPA-receptor was determined by immunohistochemical analysis. High-level uPA mRNA expression was restricted to epithelial cells of the convoluted proximal tubules and the thick ascending limb of Henle's loop (the straight part of the distal tubule). However, uPA immunoreactivity was not confined to sites of uPA mRNA expression, but was present in all segments of the tubular epithelium. Tubular epithelial cells also exhibited a consistent immunoreactivity with uPA-receptor antibody, indicative of a co-localization of the uPA antigen and its receptor in the uriniferous epithelium. We propose that the uPA antigen expression in nephron segments lacking demonstrable endogenous uPA synthesis may be the result of a uPA-receptor-mediated uptake of uPA.     

Immunocytochemical localization of Na+, K+-ATPase in the rat kidney

Summary To determine if rat kidney Na⁺, K⁺-ATPase can be localized by immunoperoxidase staining after fixation and embedding, we prepared rabbit antiserum to purified lamb kidney medulla Na⁺, K⁺-ATPase. When sodium dodecylsulfate polyacrylamide electrophoretic gels of purified lamb kidney Na⁺, K⁺-ATPase and rat kidney microsomes were treated with antiserum (1200), followed by [¹²⁵I]-Protein A and autoradiography, the rat kidney microsomes showed a prominent radioactive band coincident with the -subunit of the purified lamb kidney enzyme and a fainter radioactive band which corresponded to the -subunit. When the Na⁺, K⁺-ATPase antiserum was used for immunoperoxidase staining of paraffin and plastic sections of rat kidney fixed with Bouin's, glutaraldehyde, or paraformaldehyde, intense immunoreactive staining was present in the distal convoluted tubules, subcapsular collecting tubules, thick ascending limb of the loops of Henle, and papillary collecting ducts. Proximal convoluted tubules stained faintly, and the thin portions of the loops of Henle, straight descending portions of proximal tubules, and outer medullary collecting ducts did not stain. Staining was confined to basolateral surfaces of tubular epithelial cells. No staining was obtained with preimmune serum or primary antiserum absorbed with purified lamb kidney Na⁺, K⁺-ATPase, or with osmium tetroxide postfixation. We conclude that the basolateral membranes of the distal convoluted tubules and ascending thick limb of the loops of Henle are the major sites of immunoreactive Na⁺, K⁺-ATPase concentration in the rat kidney.Supported by Grant AM 17047 from NIH and by the Veterans Administration     

Renal carbonic anhydrase activity in DBA/2FG-pcy/pcy mice with inherited polycystic kidney disease.

DBA/2FG-pcy/pcy (D2-pcy) mice are a hereditary murine model of slowly progressive polycystic kidney disease (PKD) and characterized by the persistent excretion of acidic urine, in association with polyuria, after weaning. In this study, the activity of carbonic anhydrase (CA) and it histological distribution in the kidney of D2-pcy mice were investigated by immunohistochemistry. Significantly higher CA activity was detected in the cytosolic, but not membrane, fraction of kidney homogenates in 5-week-old D2-pcy mice than in age-matched, control DBA/2 (D2) mice, and a more rapid rate of urine acidification was noted in 11-week-old mice when acetazolamide, an inhibitor of the enzyme, was administered orally. By immunohistochemistry for the major renal CA isoenzyme (CA II), epithelial cells in the distal straight tubules and the cortical collecting ducts were stained intensely, whereas those of the proximal convoluted tubules had only weak and diffuse staining. The glomeruli, the proximal straight tubules and the ascending thin limb of Henle's loop were almost free from staining. In the cells lining cysts and/or dilated tubules, CA II activity was well preserved, although the staining intensity was considerably reduced in fully-flattened, lining cells of cysts, but no difference was found between D2-pcy and D2 mice in any segmental localization of renal CA II activity. From these results it seems that D2-pcy mice in the early stages of the cystic disease continue to secrete excess protons through the CA-mediated reaction that is stimulated for regulation of acid-base balance in the distal portion of the nephron and the collecting duct in kidney. It also suggests that monitoring urine pH may be useful in predicting the effects of early interventions on the progression of slowly developing renal cysts.