Chloride transport in microperfused interlobular ducts isolated from guinea-pig pancreas
H Ishiguro, S Naruse, M Kitagawa, T Mabuchi, T Kondo, T Hayakawa, R M Case, M C Steward, H Ishiguro, S Naruse, M Kitagawa, T Mabuchi, T Kondo, T Hayakawa, R M Case, M C Steward
Abstract
Isolated interlobular ducts from the guinea-pig pancreas secrete a HCO3--rich fluid in response to secretin. To determine the role of Cl- transporters in this process, intracellular Cl- concentration ([Cl-]i) was measured in ducts loaded with the Cl--sensitive fluoroprobe, 6-methoxy-N-ethylquinolinium chloride (MEQ). [Cl-]i decreased when the luminal Cl- concentration was reduced. This effect was stimulated by forskolin, was not dependent on HCO3- and was not inhibited by application of the anion channel/transporter inhibitor H2DIDS to the luminal membrane. It is therefore attributed to a cAMP-stimulated Cl- conductance, probably the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. [Cl-]i also decreased when the basolateral Cl- concentration was reduced. This effect was not stimulated by forskolin, was largely dependent on HCO3- and was inhibited by basolateral H2DIDS. It is therefore mediated mainly by Cl-/HCO3- exchange. With high Cl- and low HCO3- concentrations in the lumen, steady-state [Cl-]i was 25-35 mM in unstimulated cells. Stimulation with forskolin caused [Cl-]i to increase by approximately 4 mM due to activation of the luminal anion exchanger. With low Cl- and high HCO3- concentrations in the lumen to simulate physiological conditions, steady-state [Cl-]i was 10-15 mM in unstimulated cells. Upon stimulation with forskolin, [Cl-]i fell to approximately 7 mM due to increased Cl- efflux via the luminal conductance. We conclude that, during stimulation under physiological conditions, [Cl-]i decreases to very low levels in guinea-pig pancreatic duct cells, largely as a result of the limited capacity of the basolateral transporters for Cl- uptake. The resulting lack of competition from intracellular Cl- may therefore favour HCO3- secretion via anion conductances in the luminal membrane, possibly CFTR.
Figures
![Figure 1. Calibration of MEQ fluorescence for…](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/2290131/bin/tjp0539-0175-f1.jpg)
![Figure 2. Changes in [Cl − ]…](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/2290131/bin/tjp0539-0175-f2.jpg)
![Figure 3. Effects of forskolin on Cl…](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/2290131/bin/tjp0539-0175-f3.jpg)
![Figure 4. Effects of forskolin on Cl…](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/2290131/bin/tjp0539-0175-f4.jpg)
![Figure 5. Effects of luminal inhibitors on…](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/2290131/bin/tjp0539-0175-f5.jpg)
![Figure 6. Changes in [Cl − ]…](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/2290131/bin/tjp0539-0175-f6.jpg)
![Figure 7. Effects of basolateral or luminal…](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/2290131/bin/tjp0539-0175-f7.jpg)
![Figure 8. Implications of measured [Cl −…](https://www.ncbi.nlm.nih.gov/pmc/articles/instance/2290131/bin/tjp0539-0175-f8.jpg)
Source: PubMed