Concurrent and Independent HCO − 3 and Cl −; Secretion in a Human Pancreatic Duct Cell Line (CAPAN-1)

Abstract

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.

Secretagogues stimulate electrogenic HCO3–secretion in the ileum of the brushtail possum,Trichosurus vulpecula:evidence for the role of a Na+/HCO3– cotransporter

“…Similarly, the change in I sc stimulated by CCH following pretreatment with acetazolamide was of similar magnitude (⌬I sc =55±9 μA cm -2 ) as in the absence of acetazolamide (⌬I sc =61±10 μA cm -2 ) and both responses were of comparable duration (duration control, 10±1.1 min; duration plus acetazolamide, 10±0.7 min, N=7). Thus acetazolamide, at a dose in excess of that shown to inhibit carbonic anhydrase-dependent HCO 3 -secretion in the eutherian pancreas (Cheng et al, 1998), had no effect on the secretory current in the possum ileum, suggesting that the hydration of CO 2 contributes little to HCO 3 -secretion in the ileum. This was supported by the observation that the addition of serosal amiloride also had little effect on the PGE 2 -stimulated response.…”

A primary culture of guinea pig gallbladder epithelial cells that is responsive to secretagogues

“…In human gallbladder epithelia (8), differential sensitivity of Ca 2+ -and cAMP-dependent Cl − secretion to anion transport inhibitors was suggested to reflect activation of separate Cl − efflux pathways. This appears to be the case in a number of secretory epithelia, in which DIDS has been observed to block Ca 2+ -dependent Cl − currents and channels (1, 2) but has no effect on cAMP-dependent Cl − currents and channels (1,2,4,7,9,14,16). On the other hand, DPC blocks both Ca 2+ -and cAMPdependent Cl − currents and channels (1, 4, 7).…”

“…This appears to be the case in a number of secretory epithelia, in which DIDS has been observed to block Ca 2+ -dependent Cl − currents and channels (1, 2) but has no effect on cAMP-dependent Cl − currents and channels (1, 2, 4, 7, 9, 14, 16). On the other hand, DPC blocks both Ca 2+ -and cAMPdependent Cl − currents and channels (1,4,7). The molecular species underlying DIDSsensitive currents are unclear; however, DPC-sensitive, cAMP-dependent currents appear to be associated with the cystic fibrosis transmembrane conductance regulator CFTR (4,12,48).…”

The Cystic Fibrosis of Exocrine Pancreas

“…3). One obvious candidate is the vacuolar H þ -pump, but evidence at the molecular level is missing, and the function in stimulated ducts is unclear (Zhao et al 1994;Villanger et al 1995;de Ondarza and Hootman 1997;Cheng et al 1998). Recently, another study focused on other types of pumps, and it was shown that rodent pancreatic ducts express both gastric and nongastric H þ /K þ pumps, which significantly contribute to secretin-stimulated duct secretion ).…”