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CFTR functions as a bicarbonate channel in pancreatic duct cells.

Ishiguro H, Steward MC, Naruse S, Ko SB, Goto H, Case RM, Kondo T, Yamamoto A - J. Gen. Physiol. (2009)

Bottom Line: Apical HCO(3)(-) fluxes activated by cyclic AMP were independent of Cl(-) and luminal Na(+), and substantially inhibited by the CFTR blocker, CFTR(inh)-172.From the changes in pH(i), membrane potential, and buffering capacity, the flux and electrochemical gradient of HCO(3)(-) across the apical membrane were determined and used to calculate the HCO(3)(-) permeability.This suggests that CFTR functions as a HCO(3)(-) channel in pancreatic duct cells, and that it provides a significant pathway for HCO(3)(-) transport across the apical membrane.

View Article: PubMed Central - PubMed

Affiliation: Human Nutrition, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan. ishiguro@htc.nagoya-u.ac.jp

ABSTRACT
Pancreatic duct epithelium secretes a HCO(3)(-)-rich fluid by a mechanism dependent on cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane. However, the exact role of CFTR remains unclear. One possibility is that the HCO(3)(-) permeability of CFTR provides a pathway for apical HCO(3)(-) efflux during maximal secretion. We have therefore attempted to measure electrodiffusive fluxes of HCO(3)(-) induced by changes in membrane potential across the apical membrane of interlobular ducts isolated from the guinea pig pancreas. This was done by recording the changes in intracellular pH (pH(i)) that occurred in luminally perfused ducts when membrane potential was altered by manipulation of bath K(+) concentration. Apical HCO(3)(-) fluxes activated by cyclic AMP were independent of Cl(-) and luminal Na(+), and substantially inhibited by the CFTR blocker, CFTR(inh)-172. Furthermore, comparable HCO(3)(-) fluxes observed in ducts isolated from wild-type mice were absent in ducts from cystic fibrosis (Delta F) mice. To estimate the HCO(3)(-) permeability of the apical membrane under physiological conditions, guinea pig ducts were luminally perfused with a solution containing 125 mM HCO(3)(-) and 24 mM Cl(-) in the presence of 5% CO(2). From the changes in pH(i), membrane potential, and buffering capacity, the flux and electrochemical gradient of HCO(3)(-) across the apical membrane were determined and used to calculate the HCO(3)(-) permeability. Our estimate of approximately 0.1 microm sec(-1) for the apical HCO(3)(-) permeability of guinea pig duct cells under these conditions is close to the value required to account for observed rates of HCO(3)(-) secretion. This suggests that CFTR functions as a HCO(3)(-) channel in pancreatic duct cells, and that it provides a significant pathway for HCO(3)(-) transport across the apical membrane.

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Inhibition of HCO3− fluxes across the apical membrane of guinea pig pancreatic ducts by CFTRinh-172. Membrane potential–evoked changes in pHi in the presence or absence of 5 µM of luminal CFTRinh-172 as indicated. Experimental conditions were similar to those in Fig. 1 D. (A) Reduced rate of increase in pHi evoked by depolarization with 70 mM K+ when CFTRinh-172 was added to the luminal perfusate. (B) Recovery of pHi increase evoked by 70 mM K+ when CFTRinh-172 was removed from the luminal perfusate. Representative of six experiments.
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fig3: Inhibition of HCO3− fluxes across the apical membrane of guinea pig pancreatic ducts by CFTRinh-172. Membrane potential–evoked changes in pHi in the presence or absence of 5 µM of luminal CFTRinh-172 as indicated. Experimental conditions were similar to those in Fig. 1 D. (A) Reduced rate of increase in pHi evoked by depolarization with 70 mM K+ when CFTRinh-172 was added to the luminal perfusate. (B) Recovery of pHi increase evoked by 70 mM K+ when CFTRinh-172 was removed from the luminal perfusate. Representative of six experiments.

Mentions: To explore the possibility that the apical HCO3− conductance in stimulated guinea pig ducts is due to the presence of CFTR, we next tested the effect of adding the selective blocker CFTRinh-172 to the luminal perfusate (Fig. 3). The experimental conditions and protocol were otherwise similar to those used in the experiments shown in Fig. 1. 2 min after applying 5 µM CFTRinh-172 to the apical membrane, the rise in pHi evoked by switching [K+]B from 1 to 70 mM (Fig. 3 A) was significantly slower than in the absence of the blocker. The rate of increase in pHi was reduced from 0.158 ± 0.030 pH units min−1 (n = 6) to 0.066 ± 0.023 pH units min−1 (n = 6; P < 0.05), representing a mean inhibition of 61 ± 7% in the presence of CFTRinh-172.


CFTR functions as a bicarbonate channel in pancreatic duct cells.

Ishiguro H, Steward MC, Naruse S, Ko SB, Goto H, Case RM, Kondo T, Yamamoto A - J. Gen. Physiol. (2009)

Inhibition of HCO3− fluxes across the apical membrane of guinea pig pancreatic ducts by CFTRinh-172. Membrane potential–evoked changes in pHi in the presence or absence of 5 µM of luminal CFTRinh-172 as indicated. Experimental conditions were similar to those in Fig. 1 D. (A) Reduced rate of increase in pHi evoked by depolarization with 70 mM K+ when CFTRinh-172 was added to the luminal perfusate. (B) Recovery of pHi increase evoked by 70 mM K+ when CFTRinh-172 was removed from the luminal perfusate. Representative of six experiments.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2654087&req=5

fig3: Inhibition of HCO3− fluxes across the apical membrane of guinea pig pancreatic ducts by CFTRinh-172. Membrane potential–evoked changes in pHi in the presence or absence of 5 µM of luminal CFTRinh-172 as indicated. Experimental conditions were similar to those in Fig. 1 D. (A) Reduced rate of increase in pHi evoked by depolarization with 70 mM K+ when CFTRinh-172 was added to the luminal perfusate. (B) Recovery of pHi increase evoked by 70 mM K+ when CFTRinh-172 was removed from the luminal perfusate. Representative of six experiments.
Mentions: To explore the possibility that the apical HCO3− conductance in stimulated guinea pig ducts is due to the presence of CFTR, we next tested the effect of adding the selective blocker CFTRinh-172 to the luminal perfusate (Fig. 3). The experimental conditions and protocol were otherwise similar to those used in the experiments shown in Fig. 1. 2 min after applying 5 µM CFTRinh-172 to the apical membrane, the rise in pHi evoked by switching [K+]B from 1 to 70 mM (Fig. 3 A) was significantly slower than in the absence of the blocker. The rate of increase in pHi was reduced from 0.158 ± 0.030 pH units min−1 (n = 6) to 0.066 ± 0.023 pH units min−1 (n = 6; P < 0.05), representing a mean inhibition of 61 ± 7% in the presence of CFTRinh-172.

Bottom Line: Apical HCO(3)(-) fluxes activated by cyclic AMP were independent of Cl(-) and luminal Na(+), and substantially inhibited by the CFTR blocker, CFTR(inh)-172.From the changes in pH(i), membrane potential, and buffering capacity, the flux and electrochemical gradient of HCO(3)(-) across the apical membrane were determined and used to calculate the HCO(3)(-) permeability.This suggests that CFTR functions as a HCO(3)(-) channel in pancreatic duct cells, and that it provides a significant pathway for HCO(3)(-) transport across the apical membrane.

View Article: PubMed Central - PubMed

Affiliation: Human Nutrition, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan. ishiguro@htc.nagoya-u.ac.jp

ABSTRACT
Pancreatic duct epithelium secretes a HCO(3)(-)-rich fluid by a mechanism dependent on cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane. However, the exact role of CFTR remains unclear. One possibility is that the HCO(3)(-) permeability of CFTR provides a pathway for apical HCO(3)(-) efflux during maximal secretion. We have therefore attempted to measure electrodiffusive fluxes of HCO(3)(-) induced by changes in membrane potential across the apical membrane of interlobular ducts isolated from the guinea pig pancreas. This was done by recording the changes in intracellular pH (pH(i)) that occurred in luminally perfused ducts when membrane potential was altered by manipulation of bath K(+) concentration. Apical HCO(3)(-) fluxes activated by cyclic AMP were independent of Cl(-) and luminal Na(+), and substantially inhibited by the CFTR blocker, CFTR(inh)-172. Furthermore, comparable HCO(3)(-) fluxes observed in ducts isolated from wild-type mice were absent in ducts from cystic fibrosis (Delta F) mice. To estimate the HCO(3)(-) permeability of the apical membrane under physiological conditions, guinea pig ducts were luminally perfused with a solution containing 125 mM HCO(3)(-) and 24 mM Cl(-) in the presence of 5% CO(2). From the changes in pH(i), membrane potential, and buffering capacity, the flux and electrochemical gradient of HCO(3)(-) across the apical membrane were determined and used to calculate the HCO(3)(-) permeability. Our estimate of approximately 0.1 microm sec(-1) for the apical HCO(3)(-) permeability of guinea pig duct cells under these conditions is close to the value required to account for observed rates of HCO(3)(-) secretion. This suggests that CFTR functions as a HCO(3)(-) channel in pancreatic duct cells, and that it provides a significant pathway for HCO(3)(-) transport across the apical membrane.

Show MeSH
Related in: MedlinePlus