Zeng W, Lee M G, Yan M, Diaz J, Benjamin I, Marino C R, Kopito R, Freedman S, Cotton C, Muallem S, Thomas P
Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235, USA.
Am J Physiol. 1997 Aug;273(2 Pt 1):C442-55. doi: 10.1152/ajpcell.1997.273.2.C442.
Cystic fibrosis results from defective Cl- channel activity mediated by the cystic fibrosis transmembrane conductance regulator (CFTR) gene product. In the gastrointestinal tract this is manifested in abnormal salivary secretion and pancreatic insufficiency. This is generally attributed to defective Cl- transport by the ductal system of the glands. We provide the first immunocytochemical and functional evidence for expression of CFTR protein and Cl- current in rat and mouse submandibular gland (SMG) and pancreatic acinar cells, a site proximal to the ductal system of these secretory glands. Monoclonal and polyclonal antibodies recognizing COOH-terminal epitopes of CFTR show that duct and acinar cells from the two glands express CFTR in the luminal membrane. Specificity of the polyclonal antibody was verified by absence of staining in duct and acinar cells of the SMG of cf-/cf- and delta F/delta F mice. Identification of CFTR in acinar cells was aided by demonstrating coexpression of CFTR and type 3 inositol 1,4,5-trisphosphate receptors in the luminal pole of acini and absence of type 3 inositol 1,4,5-trisphosphate receptors in ducts. Electrophysiological characterization in single SMG duct and acinar cells shows the presence of a protein kinase A-activated, voltage- and time-independent, ohmic Cl- current and absence of repolarization-dependent tail currents, all of which are kinetic properties of the CFTR-dependent Cl- channel. In addition, the channel was activated by the nonhydrolyzable ATP analog 5'-adenylylimidodiphosphate and the benzimidazalone NS-004. Channels activated by all activators were inhibited by glibenclamide and a known inhibitory antiserum [anti-CFTR-(505-511)]. Combined immunologic, functional, and pharmacological evidence allows us to conclude that acinar cells of the SMG and pancreas express functional CFTR-dependent Cl- channels. Because this site is proximal to the duct, modification of activity of this channel in acinar cells is likely to contribute to abnormal salivary secretion and pancreatic insufficiency typical of cystic fibrosis.
囊性纤维化是由囊性纤维化跨膜传导调节因子（CFTR）基因产物介导的氯离子通道活性缺陷所致。在胃肠道中，这表现为唾液分泌异常和胰腺功能不全。这通常归因于腺体导管系统氯离子转运缺陷。我们首次提供了免疫细胞化学和功能证据，证明CFTR蛋白和氯离子电流在大鼠和小鼠下颌下腺（SMG）及胰腺腺泡细胞中表达，这些细胞位于这些分泌腺导管系统的近端部位。识别CFTR羧基末端表位的单克隆和多克隆抗体显示，这两种腺体的导管和腺泡细胞在腔膜中表达CFTR。通过在cf-/cf-和delta F/delta F小鼠的SMG导管和腺泡细胞中未检测到染色，验证了多克隆抗体的特异性。通过证明CFTR与腺泡腔极的3型肌醇1,4,5-三磷酸受体共表达以及导管中不存在3型肌醇1,4,5-三磷酸受体，辅助鉴定了腺泡细胞中的CFTR。对单个SMG导管和腺泡细胞的电生理特性分析显示，存在一种蛋白激酶A激活的、电压电压和时间依赖性的欧姆型氯离子电流，且不存在复极化依赖性尾电流，所有这些都是CFTR依赖性氯离子通道的动力学特性。此外，该通道可被不可水解的ATP类似物5'-腺苷酰亚胺二磷酸和苯并咪唑酮NS-004激活。所有激活剂激活的通道均被格列本脲和一种已知的抑制性抗血清[抗CFTR-(505-511)]抑制。综合免疫、功能和药理学证据，我们得出结论，SMG和胰腺的腺泡细胞表达功能性CFTR依赖性氯离子通道。由于该部位靠近导管，腺泡细胞中该通道活性的改变可能导致囊性纤维化典型的唾液分泌异常和胰腺功能不全。
