Reddy M M, Quinton P M
Division of Biomedical Sciences, University of California, Riverside 92521-0121.
J Membr Biol. 1992 Oct;130(1):49-62. doi: 10.1007/BF00233738.
Cystic fibrosis (CF) is characterized by abnormal epithelial Cl- conductance (GCl). In vitro studies that have shown that cAMP regulation is an intrinsic property of the CF-affected GCl(CF-GCl) have been carried out previously on cultured secretory cells and on nonepithelial cells. Even though GCl in absorption is defective in CF, a clear demonstration of cAMP regulation of CF-GCl in a purely absorptive tissue is lacking. We studied the cAMP regulation of CF-GCl in the microperfused intact human reabsorptive sweat duct. About 40% of the ducts responded to cAMP (responsive) while the remainder of the ducts did not. In responsive ducts, cAMP-elevating agents: beta-adrenergic agonist isoproterenol (IPR), CPT-cAMP, forskolin, theophylline or IBMX increased Gt by about 2.3-fold (n = no. of ducts = 8). Removal of media Cl-, but not amiloride pretreatment (in the lumen), abolished the cAMP response, indicating exclusive activation of GCl. cAMP activated both apical and basolateral GCl. cAMP hyperpolarized gluconate: Cl- (lumen:bath) transepithelial bionic potentials (delta Vt = -20.3 +/- 5.2 mV, mean +/- SE, n = 9) and transepithelial 3: 1 luminal NaCl dilution diffusion potentials (delta Vt = -8.8 +/- 2.9 mV, n = 5). cAMP activated basolateral GCl as indicated by increased bi-ionic (gluconate:Cl-, bath:lumen) diffusion potentials (by about 12 mV). The voltage divider ratio in symmetric NaCl solutions increased by 60%. Compared to responsive ducts, nonresponsive ducts were characterized by smaller spontaneous transepithelial potentials in symmetrical Ringer's solution (Vt = -6.9 +/- 0.8 mV, n = 24, nonresponsive vs. -19.4 +/- 1.8 mV, n = 22, responsive ducts) but larger bi-ionic potentials (-94 +/- 6 mV, n = 35, nonresponsive vs. -65 +/- 5 mV, n = 17, responsive ducts) and dilution diffusion potentials (-40 +/- 5 mV, n = 11, nonresponsive vs. -29 +/- 3 mV, n = 7, responsive ducts). These results are consistent with an inherently (prestimulus) maximal activation of GCl in nonresponsive ducts and submaximal activation of GCl in responsive ducts. We conclude that cAMP activates CF-GCl which is expressed and abnormal in both apical and basal membranes of this absorptive epithelium in CF.
囊性纤维化（CF）的特征是上皮细胞氯离子电导（GCl）异常。先前已在培养的分泌细胞和非上皮细胞上进行了体外研究，这些研究表明cAMP调节是受CF影响的GCl（CF-GCl）的固有特性。尽管CF中吸收过程中的GCl存在缺陷，但在纯吸收性组织中缺乏cAMP对CF-GCl调节的明确证据。我们研究了微灌注的完整人重吸收性汗腺导管中CF-GCl的cAMP调节。约40%的导管对cAMP有反应（反应性导管），而其余导管无反应。在反应性导管中，升高cAMP的药物：β-肾上腺素能激动剂异丙肾上腺素（IPR）、CPT-cAMP、福斯可林、茶碱或异丁基甲基黄嘌呤（IBMX）使Gt增加约2.3倍（n = 导管数量 = 8）。去除培养基中的氯离子，但管腔内预先用氨氯吡咪处理则不会消除cAMP反应，这表明GCl被特异性激活。cAMP激活了顶端和基底外侧的GCl。cAMP使葡萄糖酸盐：氯离子（管腔：浴液）跨上皮双离子电位超极化（ΔVt = -20.3 ± 5.2 mV，平均值 ± 标准误，n = 9）以及跨上皮3:1管腔氯化钠稀释扩散电位（ΔVt = -8.8 ± 2.9 mV，n = 5）。如双离子（葡萄糖酸盐：氯离子，浴液：管腔）扩散电位增加（约12 mV）所示，cAMP激活了基底外侧GCl。在对称的氯化钠溶液中，分压器比率增加了60%。与反应性导管相比，无反应性导管的特征是在对称的林格氏溶液中自发跨上皮电位较小（Vt = -6.9 ± 0.8 mV，n = 24，无反应性导管 vs. -19.4 ± 1.8 mV，n = 22，反应性导管），但双离子电位较大（-94 ± 6 mV，n = 35，无反应性导管 vs. -65 ± 5 mV，n = 17，反应性导管）以及稀释扩散电位较大（-40 ± 5 mV，n = 11，无反应性导管 vs. -29 ± 3 mV，n = 7，反应性导管）。这些结果与无反应性导管中GCl固有地（刺激前）最大激活以及反应性导管中GCl次最大激活一致。我们得出结论，cAMP激活了CF-GCl，CF-GCl在CF患者这种吸收性上皮的顶端和基底膜中均有表达且异常。
