Stimulation of Cl/HCO3 exchange in rat duodenal brush border membrane vesicles by cAMP

Dunk, C.R.; Brown, Charles D.; Turnberg, L A

doi:10.1007/bf00582138

Cited by 20 publications

(9 citation statements)

References 20 publications

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“…In this study, the most likely explanation of our results is inhibition by FURO or DIDS of HCO3-/C1-exchange coupled to Na+-HCO3 -symport (see above). The appearance of active C1-reabsorption in the presence of TERB is consistent with the known stimulation (or permission) of HCOs-/C1--exchange by TERB (Harada et al, 1991;Hayashi et al, 1991;Dunk et al, 1989;Schuster and Stokes, 1987;Schuster, 1986). Both transport processes have recently been shown (Nord et al, 1988;Lubman and Crandall, 1991) to be present in alveolar epithelial cells.…”

Section: Ion Flux Studiessupporting

confidence: 71%

Studies on the mechanisms of active ion fluxes across alveolar epithelial cell monolayers

Kim

Suh

Lubman

et al. 1992

Journal of Tissue Culture Methods

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SUMMARY: To investigate the celt physiologic and biological properties of the alveolar epithelium, we studied rat alveolar epithelial cell monolayers grown on permeable supports in primary culture. Type II alveolar epithelial cells were disaggregated using elastase, and partially purified on a discontinuous metrizamide gradient. These isolated cells were plated onto tissue culture-treated Nuclepore membrane filters at 1.5 )< 106 cells/cm 2 and maintained in a humidified incubator (5% CO2 in air, 37 ° C). After 2 days in culture, the bathing media on both sides of the cell monolayers were changed to fresh culture medium, thus removing nonadherent cells (mostly lcukocytes). These monolayers exhibit a high transmonolayer resistance (>2000 ~-cm 2) and actively transport ions. Radionuclide flux studies indicate that Na + is the predominant ionic species absorbed actively under baseline conditions, accounting for about 80% of the total active ion transport. CI-seems to be passively transported across the epithelium. However, when the epithelium is exposed to a beta-agonist (terbutaline), active absorption of Na + is increased ar, d active absorption of C1-occurs. Ahhough it is clear that both active Na + and CI-transport are dependent on Na+/K+-ATPase activity, and that Na + enters cells predominantly through channels, the specific mechanisms by which CI-enters and exits the alveolar epithelial cells remain unclear. The stimulated reabsorption of Na + and CImay be important in helping to remove excess fluid from alveolar air spaces in the lung.

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Section: Ion Flux Studiessupporting

confidence: 71%

Studies on the mechanisms of active ion fluxes across alveolar epithelial cell monolayers

Kim

Suh

Lubman

et al. 1992

Journal of Tissue Culture Methods

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“…Inhibition of this effect by colchicine, also suggests that DBcAMP acts by stimulating microtubule-dependent insertion of the transporter at the excretory domain. Activation (as well as inhibition) of Cl-/HCO3 exchanger by DBcAMP has been reported in other cell types (19,20) by modulating a cAMP-activated C1--channel. A Cl--channel has been described in the canalicular membrane of hepatocytes (21), and although its cAMPsensitivity is not known, part of the cAMP effect could be secondary to Cl--channel activation.…”

Section: Methodsmentioning

confidence: 74%

Regulation of activity and apical targeting of the Cl-/HCO3- exchanger in rat hepatocytes.

Benedetti

Strazzabosco

et al. 1994

Proc. Natl. Acad. Sci. U.S.A.

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To test the hypothesis that rat hepatocyte canalicular Cl-/HCO-exchange activity might be regulated by HCO3-or protein kinase-induced changes in the apical targeting of vesicles, isolated rat hepatocytes were cultured in the presence or absence of HCO /CO2. Cl-/HCO-exchange activity increased in cells cultured in the presence of HCO /CO2 or when stimulated by dibutyryl cAMP. Both of these effects were blocked by either colchicine or the protein kinase C agonist phorbol 12,13-dibutyrate. Fluorescence and confocal microscopy, respectively, revealed increased pericanalicular-apical membrane localization of two canalicular markers, peanut agglutinin and a 11O-kDa canalicular ectoATPase, when hepatocyte couplets were preincubated in HCO /CO2-containing medium, an effect that was again blocked by colchicine. Dibutyryl cAMP also stimulated canalicular localization of the 11O-kDa protein. These rmdings suggest that hepatocyte Cl-/HCO-exchange activity is regulated by HCO /CO2 and by protein kinase A and protein kinase C agonists through microtubule-dependent targeting of vesicles containing this exchanger to the canalicular domain.The location of individual cell surface proteins to specific membrane domains is an essential property ofepithelial cells, including hepatocytes, that establishes their structural and functional polarity. The mechanisms by which these plasma membrane proteins are localized to different cell membrane domains and the signals used to guide this "targeting" are largely unknown.In hepatocytes, the canalicular membrane represents only 13% of the plasma membrane surface and is demarcated from the basolateral cell surface by the tight junctions. This apical domain expresses specific transport systems for excretion of bile acids and other organic anions and cations (1-4).A Na+-independent Cl-/HCO-exchanger has been localized to the canalicular domain (5). This ion exchanger is the mechanism by which the hepatocyte loads acid in defense of increases in intracellular pH (pHi) above its normal set point and is activated by an alkaline load (6).We originally observed that basal Cl--dependent HCO3 fluxes were higher in rat hepatocytes cultured in the presence as opposed to the absence of HCOT/C02-containing medium. Apical insertion and removal of ion transporters have been suggested as regulatory mechanisms in cells from the renal collecting tubule that secrete H+ or HCO-in response to changes in pH of their environment (7). Therefore, we hypothesized that the increased activity of the apical Cl-/ HCO-exchanger might also involve targeting of the exchanger to the canalicular domain when stimulated by changes in pHi and HCO3.To test this hypothesis, we studied the effects of (i) HCO-/CO2, (ii) inhibitors of microtubule and microfilaments, and (iii) activators of protein kinases A and C on Cl-/HCO-exchange activity in rat hepatocyte monolayers.The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance w...

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“…Secretin also regulates HCO excretion in pancreatic ductular cells using cAMP as second intracellular messenger (28)(29)(30)(31)(32)49). Thus, cAMP appears to stimulate HCO-excretion via Cl-/HCO-exchange in epithelia that add base to the luminal side of the cell, including BDE as well as duodenum (42,50), pancreatic duct cells (28)(29)(30)(31)(32) and the cortical collecting tubules (44). In contrast, cAMP decreases the activity of the Cl/HCO-exchanger (51 ) in gallbladder epithelium, which secretes acid into the lumen.…”

Section: Isolation Of Bile Duct Epithelial Cells Male Sprague-dawleymentioning

confidence: 99%

Effect of secretion on intracellular pH regulation in isolated rat bile duct epithelial cells.

et al. 1993

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The effects of secretin on ion transport mechanisms involved in regulation of intracellular pH (pH1) and HCO3 excretion were characterized in bile duct epithelial (BDE) cells isolated from normal rat liver. pHi was measured with 2,7-bis(carboxyethyl)-5(6)-carboxy-fluorescein-acetomethylester (BCECF-AM) using a microfluorimetric method. Basal pHi of BDE was 7.04±0.06 in Hepes and 7.16±0.10 in KRB and was unaffected by secretin (50-200 nM). Recovery rates from an acid load in Hepes or in KRB media (with and without amiloride) were also not altered by secretin, indicating that Na+/H+ exchange and Na /HCO-cotransport were not affected by this hormone. After acute Cl-removal, pH1 rose 0.24±0.08 pHU at a maximal rate of 0.125±0.06 pHU/min (H' flux rates = 6.02±3.27 mM/min) and recovered after Cl-readmission (0.188±0.08 pHU/min; H' flux rates = 11.82±5.34 mM/min). Pretreatment with 1 mM DIDS inhibited the effects of Cl-removal, while valinomycin, which induces cell depolarization, enhanced these effects, probably by stimulating electrogenic HCO3 influx. Secretin significantly increased both the maximal rate of alkalinization after Cl-removal (P < 0.012) and of pH1 recovery after Cl-readmission (P < 0.025), indicating stimulation of Cl-/HCO3 exchange activity. These findings were reproducedwithN',2'-O-Dibutyryladenosine-3'-5'-cyclicmonophosphate (DBcAMP). The Cl-channel blocker 5-nitro-2'-(3-phenylpropylamino)-benzoate (NPPB, 10 AM) significantly decreased the effects of secretin and DBcAMP on the pH1 changes promoted by acute Cl-removal/readmission. These findings establish that secretin stimulates the activity of the Cl-/HCO3 exchanger in BDE cells, probably by activating Cl-channels via the intracellular messenger cAMP. This in turn depolarizes the cell, stimulating electrogenic Na /HCO3 symport. The cell depolarization induced by C1-channel activation should enhance HCO3 entrance through electrogenic Na+/HCO-symport, which in turn stimulates the Cl-/ HCO3 exchange. These mechanisms could account for secretin stimulated bicarbonate secretion in bile. (J. Clin. Invest. 1993. 92:1314-1325.) Key words: bile duct epithelium. intra-

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Stimulation of Cl/HCO3 exchange in rat duodenal brush border membrane vesicles by cAMP

Cited by 20 publications

References 20 publications

Studies on the mechanisms of active ion fluxes across alveolar epithelial cell monolayers

Studies on the mechanisms of active ion fluxes across alveolar epithelial cell monolayers

Regulation of activity and apical targeting of the Cl-/HCO3- exchanger in rat hepatocytes.

Effect of secretion on intracellular pH regulation in isolated rat bile duct epithelial cells.

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