Concurrent and independent HCO3- and Cl- secretion in a human pancreatic duct cell line (CAPAN-1).
The present study investigated both HCO-3 and Cl- secretions in a human pancreatic duct cell line, CAPAN-1, using the short-circuit current (Isc) technique. In Cl-/HCO-3-containing solution, secretin (1 microM) or forskolin (10 microM) stimulated a biphasic rise in the Isc 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 Isc while the plateau remained. In HCO-3/CO2-free solution, on the contrary, only the initial transient increase in Isc 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 Isc response, and the plateau level observed under this condition was similar to that obtained in Cl--free solution, suggesting that Cl--dependent Isc was also Na+-dependent. Bumetanide (50 microM), an inhibitor of the Na+-K+-2Cl- cotransporter, and Ba2+ (1 mm), a K+ channel blocker, could reduce the forskolin-induced Isc 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 Isc could be significantly reduced by carbonic anhydrase inhibitor, acetazolamide (45 microM). Basolateral application of amiloride (100 microM) inhibited the Isc; however, a specific Na+-H+ exchanger blocker, 5-N-methyl-N-isobutylamiloride (MIA, 5-10 microM) was found to be ineffective, excluding the involvement of the Na+-H+ exchanger. However, an inhibitor of H+-ATPase, N-ethylmaleimide did suppress the Isc (IC50 = 22 microM). Immunohistochemical studies also confirmed the presence of a vacuolar type of H+-ATPase in these cells. H2DIDS (100 microM), 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 microM) or SITS (100 microM), exerted an inhibitory effect on both Cl- and HCO-3-dependent forskolin-induced Isc 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.
Cheng
H S
HS
Department of Physiology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, Hong Kong.
Leung
P Y
PY
Cheng Chew
S B
SB
Leung
P S
PS
Lam
S Y
SY
Wong
W S
WS
Wang
Z D
ZD
Chan
H C
HC
D017920:Antiporters / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002256:Carbonic Anhydrases / Q000378:metabolism; D002460:Cell Line; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D006801:Humans; D010183:Pancreatic Ducts / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D017494:Proton Pumps / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012964:Sodium / Q000502:physiology; D025262:Vacuolar Proton-Translocating ATPases
D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D017494:Proton Pumps; D012964:Sodium; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases; D002256:Carbonic Anhydrases