The present study investigated both HCO− 3 and Cl− secretions in a human pancreatic duct cell line, CAPAN-1, using the short-circuit current (I sc ) technique. In Cl−/HCO− 3-containing solution, secretin (1 μm) or forskolin (10 μm) stimulated a biphasic rise in the I sc which initially reached a peak level at about 3 min and then decayed to a plateau level after 7 min. Removal of external Cl− abolished the initial transient phase in the forskolin-induced I sc while the plateau remained. In HCO− 3/CO2-free solution, on the contrary, only the initial transient increase in I sc was prominent. Summation of the current magnitudes observed in Cl−-free and HCO− 3-free solutions over a time course of 10 min gave rise to a curve which was similar, both in magnitude and kinetics, to the current observed in Cl−/HCO− 3-containing solution. Removal of external Na+ greatly reduced the initial transient rise in the forskolin-induced I sc response, and the plateau level observed under this condition was similar to that obtained in Cl−-free solution, suggesting that Cl−-dependent I sc was also Na+-dependent. Bumetanide (50 μm), an inhibitor of the Na+-K+-2Cl− cotransporter, and Ba2+ (1 mm), a K+ channel blocker, could reduce the forskolin-induced I sc obtained in Cl−/HCO− 3-containing or HCO− 3-free solution. However, they were found to be ineffective when external Cl− was removed, indicating the involvement of these mechanisms in Cl− secretion. On the contrary, the HCO− 3-dependent (in the absence of external Cl−) forskolin-induced I sc could be significantly reduced by carbonic anhydrase inhibitor, acetazolamide (45 μm). Basolateral application of amiloride (100 μm) inhibited the I sc ; however, a specific Na+-H+ exchanger blocker, 5-N-methyl-N-isobutylamiloride (MIA, 5–10 μm) was found to be ineffective, excluding the involvement of the Na+-H+ exchanger. However, an inhibitor of H+-ATPase, N-ethylmaleimide did suppress the I sc (IC50= 22 μm). Immunohistochemical studies also confirmed the presence of a vacuolar type of H+-ATPase in these cells. H2DIDS (100 μm), an inhibitor of Na+-HCO− 3 cotransporter, was without effect. Apical addition of Cl− channel blocker, diphenylamine-2,2′-dicarboxylic acid (DPC, 1 mm), but not disulfonic acids, DIDS (100 μm) or SITS (100 μm), exerted an inhibitory effect on both Cl− and HCO− 3-dependent forskolin-induced I sc responses. Histochemical studies showed discrete stainings of carbonic anhydrase in the monolayer of CAPAN-1 cells, suggesting that HCO− 3 secretion may be specialized to a certain population of cells. The present results suggest that both HCO− 3 and Cl− secretion by the human pancreatic duct cells may occur concurrently and independently.
The Journal of Membrane Biology – Springer Journals
Published: Jul 15, 1998
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