al-Nakkash L, Cotton C U
Department of Pediatrics, Case Western Reserve University, Cleveland, Ohio 44106-4948, USA.
Am J Physiol. 1997 Jul;273(1 Pt 1):G204-16. doi: 10.1152/ajpgi.1997.273.1.G204.
Secretion of salt and water by the epithelial cells that line pancreatic ducts depends on activation of apical membrane Cl- conductance. In the present study, we characterized two types of Cl- conductances present in the apical cell membrane of bovine pancreatic duct epithelial cells. Primary cultures of bovine main pancreatic duct epithelium and an immortalized cell line (BPD1) derived from primary cultures were used. Elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) or Ca2+ in intact monolayers of duct epithelium induced sustained anion secretion. Agonist-induced changes in plasma membrane Cl- permeability were accessed by 36 Cl- efflux, whole cell current recording, and measurements of transepithelial Cl- current across permeabilized epithelial monolayers. Elevation of intracellular cAMP elicited a sustained increase in Cl- permeability, whereas elevation of intracellular Ca2+ induced only a transient increase in Cl- permeability. Ca(2+)- but not cAMP-induced increases in Cl- permeability were abolished by preincubation of cells with the Ca2+ buffer 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl) ester (BAPTA-AM). N-phenylanthranilic acid (DPC; 1 mM) and glibenclamide (100 microM), but not 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 500 microM), inhibited the cAMP-induced increase in Cl- permeability. In contrast, DPC and DIDS, but not glibenclamide, inhibited the Ca(2+)-induced increase in Cl- permeability. We conclude from these experiments that bovine pancreatic duct epithelial cells express at least two types of Cl- channels, cAMP and Ca2+ activated, in the apical cell membrane. Because the Ca(2+)-activated increase in Cl- permeability is transient, the extent to which this pathway contributes to sustained anion secretion by the ductal epithelium remains to be determined.
胰腺导管内衬的上皮细胞分泌盐和水取决于顶端膜氯离子电导的激活。在本研究中，我们对牛胰腺导管上皮细胞顶端细胞膜中存在的两种氯离子电导进行了特性描述。使用了牛主胰管上皮的原代培养物以及从原代培养物衍生的永生化细胞系（BPD1）。在完整的导管上皮单层细胞中，细胞内3',5'-环磷酸腺苷（cAMP）或钙离子（Ca2+）浓度升高会诱导持续的阴离子分泌。通过36Cl-外流、全细胞电流记录以及跨通透化上皮单层细胞的跨上皮氯离子电流测量来检测激动剂诱导的质膜氯离子通透性变化。细胞内cAMP浓度升高会引起氯离子通透性持续增加，而细胞内Ca2+浓度升高仅诱导氯离子通透性短暂增加。用钙离子缓冲剂1,2-双（2-氨基苯氧基）乙烷-N,N,N',N'-四乙酸四（乙酰氧甲基）酯（BAPTA-AM）预孵育细胞后，可消除由Ca2+而非cAMP诱导的氯离子通透性增加。N-苯基邻氨基苯甲酸（DPC；1 mM）和格列本脲（100 microM）可抑制cAMP诱导的氯离子通透性增加，但4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS；500 microM）则不能。相反，DPC和DIDS可抑制Ca2+诱导的氯离子通透性增加，而格列本脲则不能。我们从这些实验得出结论，牛胰腺导管上皮细胞在顶端细胞膜中表达至少两种类型的氯离子通道，即cAMP激活型和Ca2+激活型。由于Ca2+激活的氯离子通透性增加是短暂的，该途径对导管上皮持续阴离子分泌的贡献程度仍有待确定。
