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I David Weiner

Publications and source records attributed to I David Weiner.

18 recordsLinked to original sources
PubMed2007

Molecular mechanisms of renal ammonia transport.

Acid-base homeostasis to a great extent relies on renal ammonia metabolism. In the past several years, seminal studies have generated important new insights into the mechanisms of renal ammonia transport. In particular, the theory that ammonia transport occurs almost exclusively through nonionic NH(3) diffusion and NH(4)(+) trapping has given way to a model postulating that a variety of proteins specifically transport NH(3) and NH(4)(+) and that this transport is critical for normal ammonia metabolism. Many of these proteins transport primarily H(+) or K(+) but also transport NH(4)(+). Nonerythroid Rh glycoproteins transport ammonia and may represent critical facilitators of ammonia transport in the kidney. This review discusses the underlying aspects of renal ammonia transport as well as specific proteins with important roles in renal ammonia transport.

Ammonia↗
PubMed2006

Expression of the ammonia transporter, rh C glycoprotein, in normal and neoplastic human kidney.

Recent studies have identified the presence of a novel Mep/Amt/Rh glycoprotein family of proteins that may play an important role in transmembrane ammonia transport. One of the mammalian members of this family, Rh C glycoprotein (RhCG), transports ammonia, is expressed in distal nephron sites that are critically important for ammonia secretion, exhibits increased expression in response to chronic metabolic acidosis, and originally was cloned as a tumor-related protein. The purpose of our studies was to determine the localization of RhCG in the normal and neoplastic human kidney. Immunoblot analysis of human renal cortical protein lysates demonstrated RhCG protein expression with a molecular weight of approximately 52 kD. Immunohistochemistry revealed both apical and basolateral Rhcg expression in the distal convoluted tubule, connecting segment, and initial collecting tubule and throughout the collecting duct. Co-localization with calbindin-D28k, H(+)-ATPase, aquaporin-2, and pendrin showed that distal convoluted tubule and connecting segment cells, A-type intercalated cells, and non-A, non-B cells express RhCG and that B-type intercalated cells, principal cells, and inner medullary collecting duct cells do not. In renal neoplasms, RhCG was expressed by chromophobe renal cell carcinoma and renal oncocytoma but not by clear cell renal cell carcinoma or by papillary renal cell carcinomas. These studies suggest that RhCG contributes to both apical and basolateral membrane ammonia transport in the human kidney. Furthermore, renal chromophobe renal cell carcinoma and renal oncocytoma seem to originate from the A-type intercalated cell.

Adenocarcinoma, Follicular↗
PubMed2006

Cellular distribution of the potassium channel KCNQ1 in normal mouse kidney.

Mechanisms of K(+) secretion and absorption along the collecting duct are not understood fully. Because KCNQ1 participates in K(+) secretion within the inner ear and stomach, distribution of KCNQ1 in mouse kidney was studied using Northern and Western analyses, RT-PCR of isolated tubules, and immunohistochemistry. Northern blots demonstrated KCNQ1 transcripts in whole kidney. RT-PCR showed KCNQ1 mRNA in isolated distal convoluted tubule (DCT), connecting segment (CNT), collecting ducts (CD), and glomeruli. Immunoblots of kidney and stomach revealed a approximately 75-kDa protein, the expected mobility for KCNQ1. KCNQ1 was detected by immunohistochemistry throughout the distal nephron and CD. Thick ascending limbs exhibited weak basolateral immunolabel. In DCT and CNT cells, immunolabel was intense and basolateral, although KCNQ1 label was stronger in late than in early DCT. Initial collecting tubule and cortical CD KCNQ1 immunolabel was predominantly diffuse, but many cells exhibited discrete apical label. Double-labeling experiments demonstrated that principal cells, type B intercalated cells, and a few type A intercalated cells exhibited distinct apical KCNQ1 immunolabel. In inner medullary CD, principal cells exhibited distinct basolateral KCNQ1 immunolabel, whereas intercalated cells showed diffuse cytoplasmic staining. Thus KCNQ1 protein is widely distributed in mouse distal nephron and CD, with significant axial and cellular heterogeneity in location and intensity. These findings suggest that KCNQ1 has cell-specific roles in renal ion transport and may participate in K(+) secretion and/or absorption along the thick ascending limb, DCT, connecting tubule, and CD.

Animals↗
PubMed2006

Changes in subcellular distribution of the ammonia transporter, Rhcg, in response to chronic metabolic acidosis.

The primary mechanism by which the kidneys mediate net acid excretion is through ammonia metabolism. In the current study, we examined whether chronic metabolic acidosis, which increases ammonia metabolism, alters the cell-specific and/or the subcellular expression of the ammonia transporter family member, Rhcg, in the outer medullary collecting duct in the inner stripe (OMCDi). Chronic metabolic acidosis was induced in normal SD rats by HCl ingestion for 7 days; controls were pair-fed. The subcellular distribution of Rhcg was determined using immunogold electron microscopy and morphometric analyses. In intercalated cells, acidosis increased total Rhcg, apical plasma membrane Rhcg, and the proportion of total cellular Rhcg in the apical plasma membrane. Intracellular Rhcg decreased significantly, and basolateral Rhcg was unchanged. Because apical plasma membrane length increased in parallel with apical Rhcg immunolabel, apical plasma membrane Rhcg density was unchanged. In principal cells, acidosis increased total Rhcg, apical plasma membrane Rhcg, and the proportion of total cellular Rhcg in the apical plasma membrane while decreasing the intracellular proportion. In contrast to the intercalated cell, chronic metabolic acidosis did not significantly alter apical boundary length; accordingly, apical plasma membrane Rhcg density increased. In addition, basolateral Rhcg immunolabel increased in response to chronic metabolic acidosis. These results indicate that in the rat OMCDi 1) chronic metabolic acidosis increases apical plasma membrane Rhcg in both the intercalated cell and principal cell where it may contribute to enhanced apical ammonia secretion; 2) increased apical plasma membrane Rhcg results from both increased total protein and changes in the subcellular distribution of Rhcg; 3) the mechanism of Rhcg subcellular redistribution differs in intercalated and principal cells; and 4) Rhcg may contribute to regulated basolateral ammonia transport in the principal cell.

Acidosis↗
PubMed2005

Renal expression of the ammonia transporters, Rhbg and Rhcg, in response to chronic metabolic acidosis.

Chronic metabolic acidosis induces dramatic increases in net acid excretion that are predominantly due to increases in urinary ammonia excretion. The current study examines whether this increase is associated with changes in the expression of the renal ammonia transporter family members, Rh B glycoprotein (Rhbg) and Rh C glycoprotein (Rhcg). Chronic metabolic acidosis was induced in Sprague-Dawley rats by HCl ingestion for 1 wk; control animals were pair-fed. After 1 wk, metabolic acidosis had developed, and urinary ammonia excretion increased significantly. Rhcg protein expression was increased in both the outer medulla and the base of the inner medulla. Intercalated cells in the outer medullary collecting duct (OMCD) and in the inner medullary collecting duct (IMCD) in acid-loaded animals protruded into the tubule lumen and had a sharp, discrete band of apical Rhcg immunoreactivity, compared with a flatter cell profile and a broad band of apical immunolabel in control kidneys. In addition, basolateral Rhcg immunoreactivity was observed in both control and acidotic kidneys. Cortical Rhcg protein expression and immunoreactivity were not detectably altered. Rhcg mRNA expression was not significantly altered in the cortex, outer medulla, or inner medulla by chronic metabolic acidosis. Rhbg protein and mRNA expression were unchanged in the cortex, outer and inner medulla, and no changes in Rhbg immunolabel were evident in these regions. We conclude that chronic metabolic acidosis increases Rhcg protein expression in intercalated cells in the OMCD and in the IMCD, where it is likely to mediate an important role in the increased urinary ammonia excretion.

Acidosis, Renal Tubular↗
PubMed2005

Intercalated cell H+/OH- transporter expression is reduced in Slc26a4 null mice.

Slc26a4 (Pds) encodes pendrin, a Cl(-)/HCO(3)(-) exchanger expressed in the apical region of type B and non-A, non-B cells, which mediates secretion of OH(-) equivalents. Thus genetic disruption of Slc26a4 leads to systemic alkalosis in some treatment models. However, humans and mice with genetic disruption of Slc26a4 have normal acid-base balance under basal conditions. Thus we asked: 1) Is net acid excretion altered in Slc26a4 (-/-) mice under basal conditions? 2) In the absence of pendrin-mediated OH(-) secretion, are increases in intracellular and systemic pH minimized through changes in intercalated cell subtype abundance or intercalated cell H(+)/OH(-) transporter expression? To answer these questions, net acid excretion and H(+)/OH(-) transporter expression were examined in Slc26a4 (-/-) and Slc26a4 (+/+) mice using balance studies, immunolocalization, and immunoblotting. Excretion of ammonium, titratable acid, and citrate were the same in Slc26a4 null and wild-type mice. However, urinary pH and Pco(2) were much lower in Slc26a4 null relative to wild-type mice due to reduced urinary buffering of secreted H(+) by HCO(3)(-). Abundance of non-A, but not type A intercalated cells, was reduced within the cortical collecting ducts of Slc26a4 null mice. Moreover, kidneys from Slc26a4 null mice had reduced H(+)-ATPase, NBC3 and RhBG total protein expression, particularly within type B and non-A, non-B intercalated cells, although RhCG protein expression was unchanged. Reduced intercalated cell H(+)/OH(-) transporter expression is observed in Slc26a4 null mice, which likely attenuates the rise in intracellular and systemic pH expected with genetic disruption of Slc26a4.

Animals↗
PubMed2005

Characterization of ammonia transport by the kidney Rh glycoproteins RhBG and RhCG.

The erythrocyte Rh-associated glycoprotein (RhAG) was recently found to mediate transport of ammonia/ammonium when expressed in Xenopus laevis oocytes and yeast Saccharomyces cerevisiae. Nonerythroid homologs, RhBG and RhCG, are expressed in the mammalian kidney connecting segment and the collecting duct, major sites of urinary ammonia secretion. This study characterizes the transport properties of murine RhBG and RhCG by ammonium analog [14C]methylamine (MA) uptake and two-electrode voltage clamping of X. laevis oocytes. Both RhBG and RhCG mediated transport of ammonia, but differed in affinity for substrate (K(m) = 2.5 and 10 mM, respectively). The rates of RhBG- and RhCG-mediated transport were sensitive to the concentration of the protonated MA species and were stimulated by extracellular alkalosis and inhibited by acidosis, suggesting a role for H+ in the transport process. Whereas expression of RhBG or RhCG caused a small increase in plasma membrane conductance, [14C]MA uptake was not affected by depolarization of oocytes with 100 mM extracellular K+ or by clamping the membrane potential between 0 and -100 mV, indicating that RhBG- and RhCG-mediated transport was independent of the membrane potential. These results strongly suggest that RhBG and RhCG transport ammonia by an electroneutral process that involves NH4(+)/H+ exchange resulting in net NH3 translocation. The polarized localization of RhBG and RhCG in kidney tubules and the different substrate affinities may enable these proteins to participate in transepithelial ammonia secretion and to therefore play an important role in whole animal acid-base regulation.

Ammonia↗
PubMed2005

Apical ammonia transport by the mouse inner medullary collecting duct cell (mIMCD-3).

The collecting duct is the primary site of urinary ammonia secretion; the current study determines whether apical ammonia transport in the mouse inner medullary collecting duct cell (mIMCD-3) occurs via nonionic diffusion or a transporter-mediated process and, if the latter, presents the characteristics of this apical ammonia transport. We used confluent cells on permeable support membranes and examined apical uptake of the ammonia analog [(14)C]methylammonia ([(14)C]MA). mIMCD-3 cells exhibited both diffusive and saturable, transporter-mediated, nondiffusive apical [(14)C]MA transport. Transporter-mediated [(14)C]MA uptake had a K(m) of 7.0 +/- 1.5 mM and was competitively inhibited by ammonia with a K(i) of 4.3 +/- 2.0 mM. Transport activity was stimulated by both intracellular acidification and extracellular alkalinization, and it was unaltered by changes in membrane voltage, thereby functionally identifying an apical, electroneutral NH(4)(+)/H(+) exchange activity. Transport was bidirectional, consistent with a role in ammonia secretion. In addition, transport was not altered by Na(+) or K(+) removal, not inhibited by luminal K(+), and not mediated by apical H(+)-K(+)-ATPase, Na(+)-K(+)-ATPase, or Na(+)/H(+) exchange. Finally, mIMCD-3 cells express the recently identified ammonia transporter family member Rh C glycoprotein (RhCG) at its apical membrane. These studies indicate that the renal collecting duct cell mIMCD-3 has a novel apical, electroneutral Na(+)- and K(+)-independent NH(4)(+)/H(+) exchange activity, possibly mediated by RhCG, that is likely to mediate important components of collecting duct ammonia secretion.

Acids↗
PubMed2004

Expression of the ammonia transporter proteins Rh B glycoprotein and Rh C glycoprotein in the intestinal tract.

Ammonia metabolism is important in multiple aspects of gastrointestinal physiology, but the mechanisms of ammonia transport in the gastrointestinal tract remain incompletely defined. The present study examines expression of the ammonia transporter family members Rh B glycoprotein (RhBG) and Rh C glycoprotein (RhCG) in the mouse gastrointestinal tract. Real-time RT-PCR amplification and immunoblot analysis identified mRNA and protein for both RhBG and RhCG were expressed in stomach, duodenum, jejunum, ileum, and colon. Immunohistochemistry showed organ and cell-specific expression of both RhBG and RhCG. In the stomach, both RhBG and RhCG were expressed in the fundus and forestomach, but not in the antrum. In the forestomach, RhBG was expressed by all nucleated squamous epithelial cells, whereas RhCG was expressed only in the stratum germinativum. In the fundus, RhBG and RhCG immunoreactivity was present in zymogenic cells but not in parietal or mucous cells. Furthermore, zymogenic cell RhBG and RhCG expression was polarized, with apical RhCG and basolateral RhBG immunoreactivity. In the duodenum, jejunum, ileum, and colon, RhBG and RhCG immunoreactivity was present in villous, but not in mucous or crypt cells. Similar to the fundic zymogenic cell, RhBG and RhCG expression in villous epithelial cells was polarized when apical RhCG and basolateral RhBG immunoreactivity was present. Thus the ammonia transporting proteins RhBG and RhCG exhibit cell-specific, axially heterogeneous, and polarized expression in the intestinal tract suggesting they function cooperatively to mediate gastrointestinal tract ammonia transport.

Animals↗
PubMed2004

Basolateral ammonium transport by the mouse inner medullary collecting duct cell (mIMCD-3).

The renal collecting duct is the primary site for the ammonia secretion necessary for acid-base homeostasis. Recent studies have identified the presence of putative ammonia transporters in the collecting duct, but whether the collecting duct has transporter-mediated ammonia transport is unknown. The purpose of this study was to examine basolateral ammonia transport in the mouse collecting duct cell (mIMCD-3). To examine mIMCD-3 basolateral ammonia transport, we used cells grown to confluence on permeable support membranes and quantified basolateral uptake of the radiolabeled ammonia analog [14C]methylammonia ([14C]MA). mIMCD-3 cell basolateral MA transport exhibited both diffusive and transporter-mediated components. Transporter-mediated uptake exhibited a Km for MA of 4.6 +/- 0.2 mM, exceeded diffusive uptake at MA concentrations below 7.0 +/- 1.8 mM, and was competitively inhibited by ammonia with a Ki of 2.1 +/- 0.6 mM. Transporter-mediated uptake was not altered by inhibitors of Na+-K+-ATPase, Na+-K+-2Cl(-) cotransporter, K+ channels or KCC proteins, by excess potassium, by extracellular sodium or potassium removal or by varying membrane potential, suggesting the presence of a novel, electroneutral ammonia-MA transport mechanism. Increasing the outwardly directed transmembrane H+ gradient increased transport activity by increasing Vmax. Finally, mIMCD-3 cells express mRNA and protein for the putative ammonia transporter Rh B-glycoprotein (RhBG), and they exhibit basolateral RhBG immunoreactivity. We conclude that mIMCD-3 cells express a basolateral electroneutral NH4+/H+ exchange activity that may be mediated by RhBG.

Acid-Base Equilibrium↗
PubMed2004

The Rh gene family and renal ammonium transport.

PURPOSE OF REVIEW: Renal acid-base homeostasis, to a very large extent, depends on renal ammonia production and transport. A putative ammonia transporter family of proteins has recently been identified, and at least two members of this family are expressed in the renal connecting segment and collecting duct. The purpose of this review is to discuss key features of renal ammonia metabolism and transport, with particular emphasis on the transporters involved in this process. RECENT FINDINGS: The putative ammonia transporter family members, RhBG and RhCG, are expressed in the renal connecting segment and collecting duct. Basolateral RhBG is expressed by all cells in the connecting segment and cortical collecting duct, and by intercalated cells in the outer medullary and inner medullary collecting duct. Apical RhCG is expressed in the same distribution and also in the outer stripe of the outer medullary collecting duct principal cells. In all regions, the expression of RhBG and RhCG is greater in intercalated cells than in principal cells. The related protein, RhAG, appears to be an erythroid-specific protein that mediates ammonium/hydrogen ion (NH4/H) exchange. RhBG and RhCG appear to be sodium and potassium ion-independent ammonia transporters. Whether they mediate electrogenic ammonia transport or electroneutral ammonia/hydrogen ion exchange remains an active area of investigation. Finally, transport studies have identified that electroneutral ammonium/hydrogen ion exchange is present in the collecting duct. SUMMARY: The Rh glycoproteins, RhBG and RhCG, appear to mediate important roles in renal ammonia transport, and therefore in acid-base homeostasis.

Animals↗
PubMed2003

Localization of the ammonium transporters, Rh B glycoprotein and Rh C glycoprotein, in the mouse liver.

BACKGROUND & AIMS: Hepatic ammonium metabolism is critical for maintenance of normal health. Three mammalian members of an ammonium transporter family have recently been identified: Rh A glycoprotein (RhAG), Rh B glycoprotein (RhBG), and Rh C glycoprotein (RhCG). This study examined which of these are expressed in the mouse liver and in which cells they are expressed. METHODS: Normal Balb/c mice were used. Messenger RNA (mRNA) expression was detected using either conventional or real-time reverse-transcription polymerase chain reaction (RT-PCR). Protein expression was examined using immunoblot analysis and either immunohistochemical or immunofluorescent microscopy. RESULTS: We confirmed hepatic RhBG mRNA expression using real-time RT-PCR. Immunoblot analysis identified expression of a approximately 45-kilodalton protein. Immunohistochemical and immunofluorescent microscopy identified basolateral RhBG immunoreactivity in 1-2 cell layers of hepatocytes surrounding central veins. No immunoreactivity was identified in periportal or midzonal hepatocytes. Perivenous hepatocyte-specific expression was confirmed by colocalization with glutamine synthetase. A second ammonium transporter, RhCG, was expressed but at substantially lower levels. Real-time RT-PCR quantified hepatic RhCG mRNA expression at approximately 0.4% of RhBG mRNA expression. Immunoblot analysis confirmed RhCG protein expression, and immunofluorescence microscopy identified RhCG expression in bile duct epithelia. In contrast to RhBG and RhCG, RhAG mRNA was not identified by RT-PCR. CONCLUSIONS: RhBG and RhCG are expressed by the mouse liver. Basolateral RhBG is expressed by perivenous hepatocytes, where it may mediate ammonium uptake, and RhCG immunoreactivity is present in bile duct epithelial cells, where it may contribute to ammonium secretion into bile fluid.

Animals↗
PubMed2002

Localization of the ammonium transporter proteins RhBG and RhCG in mouse kidney.

Ammonia is both produced and transported by renal epithelial cells, and it regulates renal ion transport. Recent studies have identified a family of putative ammonium transporters; mRNA for two members of this family, Rh B-glycoprotein (RhBG) and Rh C-glycoprotein (RhCG), is expressed in the kidney. The purpose of this study was to determine the cellular location of RhBG and RhCG protein in the mouse kidney. We generated RhBG- and RhCG-specific anti-peptide antibodies. Immunoblot analysis confirmed that both proteins were expressed in the mouse kidney. RhBG localization with immunohistochemistry revealed discrete basolateral labeling in the connecting segment (CNT) and in the majority of initial collecting tubule (ICT) and cortical collecting duct (CCD) cells. In the outer medullary collecting duct (OMCD) and inner medullary collecting duct (IMCD) only a subpopulation of cells exhibited basolateral immunoreactivity. Colocalization of RhBG with carbonic anhydrase II, the thiazide-sensitive transporter, and the anion exchangers AE1 and pendrin demonstrated RhBG immunoreactivity in all CNT cells and all CCD and ICT principal cells. In the ICT and CCD, basolateral RhBG immunoreactivity is also present in A-type intercalated cells but not in pendrin-positive CCD intercalated cells. In the OMCD and IMCD, only intercalated cells exhibit RhBG immunoreactivity. Immunoreactivity for a second putative ammonium transporter, RhCG, was present in the apical region of cells with almost the same distribution as RhBG. However, RhCG immunoreactivity was present in all CCD cells, and it was present in outer stripe OMCD principal cells, in addition to OMCD and IMCD intercalated cells. Thus the majority of RhBG and RhCG protein expression is present in the same epithelial cell types in the CNT and collecting duct but with opposite polarity. These findings suggest that RhBG and RhCG may play important and cell-specific roles in ammonium transport and signaling in these regions of the kidney.

Animals↗
PubMed2002

Expression and developmental regulation of the NMDA receptor subunits in the kidney and cardiovascular system.

Antagonists to the N-methyl-D-aspartate (NMDA) receptor bind to various extraneuronal tissues. We therefore assessed the expression of the main NMDA subunit, NR1, in various tissues. We demonstrate that NR1 appears to be most abundant in the rat kidney and heart. NR1 is present in total rat kidney, cortex, and medulla. Of the NR2 subunits, only the NR2C subunit protein is present in the kidney. The abundance of the NR1 subunit protein increases with kidney development. Both NR1 and NR2C are present in opossum kidney, Madin-Darby canine kidney, and LLC-PK(1) cells. Immunohistochemistry studies show that the NR1 subunit is present in the renal proximal tubule. NR1 is abundant in the atrium and ventricle but is also expressed in the aorta and pulmonary artery. The NR2 subunits are not expressed in the heart. NR1 subunit protein expression is constant throughout heart development. Finally, the NR1 subunit protein is expressed in heart cells (H9c2) grown in culture. These studies reveal the presence of the NMDA receptor in the kidney and the cardiovascular system.

Aging↗
PubMed2002

Mechanisms through which ammonia regulates cortical collecting duct net proton secretion.

Ammonia stimulates cortical collecting duct (CCD) net bicarbonate reabsorption by activating an apical H(+)-K(+)-ATPase through mechanisms that are independent of ammonia's known effects on intracellular pH and active sodium transport. The present studies examined whether this stimulation occurs through soluble N-ethylmaleimide-sensitive fusion attachment receptor (SNARE) protein-mediated vesicle fusion. Rabbit CCD segments were studied using in vitro microperfusion, and transepithelial bicarbonate transport was measured using microcalorimetry. Ammonia's stimulation of bicarbonate reabsorption was blocked by either chelating intracellular calcium with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester or by inhibiting microtubule polymerization with colchicine compared with parallel studies performed in the absence of these inhibitors. An inactive structural analog of colchicine, lumicolchicine, did not alter ammonia's stimulation of bicarbonate reabsorption. Tetanus toxin, a zinc endopeptidase specific for vesicle-associated SNARE (v-SNARE) proteins, prevented ammonia from stimulating net bicarbonate reabsorption. Consistent with the functional evidence for v-SNARE involvement, antibodies directed against a conserved region of isoforms 1-3 of the tetanus toxin-sensitive, vesicle-associated membrane protein (VAMP) members of v-SNARE proteins labeled the apical and subapical region of collecting duct intercalated cells. Similarly, antibodies to NSF protein, a protein involved in activation of SNARE proteins for subsequent vesicle fusion, localized to the apical and subapical region of collecting duct intercalated cells. These results indicate that ammonia stimulates CCD bicarbonate reabsorption through an intracellular calcium-dependent, microtubule-dependent, and v-SNARE-dependent mechanism that appears to involve insertion of cytoplasmic vesicles into the apical plasma membrane of CCD intercalated cells.

Acids↗
PubMed2001

Effects of ammonia on acid-base transport by the B-type intercalated cell.

Ammonia, in addition to its role as a constituent of urinary net acid excretion, stimulates cortical collecting duct (CCD) net bicarbonate reabsorption. The current study sought to begin determining the cellular transport processes through which ammonia regulates bicarbonate reabsorption by testing whether ammonia stimulates B-type intercalated cell bicarbonate secretion, bicarbonate reabsorption, or both. The effects of ammonia on single CCD intercalated cells was studied by use of measurements of intracellular pH taken from in vitro microperfused CCD segments after luminal loading of the pH-sensitive fluorescent dye BCECF. These results showed, first, that ammonia inhibited B-cell unidirectional bicarbonate secretion and that this occurred despite no effect of ammonia on apical Cl(-)/HCO(3)(-) exchange activity. Second, ammonia increased the contribution of a SCH28080-sensitive apical H(+)-K(+)-ATPase to basal intracellular pH regulation and it stimulated basolateral Cl(-)/HCO(3)(-) exchange activity. Thus, ammonia activated both apical proton secretion and basolateral base exit, consistent with stimulation of unidirectional bicarbonate reabsorption. It was concluded that ammonia regulates CCD net bicarbonate reabsorption, at least in part, through the coordinated regulation of the separate processes of B-cell bicarbonate reabsorption and bicarbonate secretion. These effects do not reflect a general activation of ion transport but, instead, reflect coordinated and specific regulation of ion transport.

Absorption↗