Sørensen J B, Larsen E H
August Krogh Institute, University of Copenhagen, DK-2100 Copenhagen O, Denmark.
J Gen Physiol. 1998 Jul;112(1):19-31. doi: 10.1085/jgp.112.1.19.
Chloride channels in the luminal membrane of exocrine gland acini from frog skin (Rana esculenta) constituted a single homogeneous population. In cell-attached patches, channels activated upon exposure to isoproterenol, forskolin, or dibutyryl-cAMP and isobutyl-1-methyl-xanthine rectified in the outward direction with a conductance of 10.0 +/- 0.4 pS for outgoing currents. Channels in stimulated cells reversed at 0 mV applied potential, whereas channels in unstimulated cells reversed at depolarized potentials (28.1 +/- 6.7 mV), indicating that Cl- was above electrochemical equilibrium in unstimulated, but not in stimulated, cells. In excised inside-out patches with 25 mM Cl- on the inside, activity of small (8-pS) linear Cl--selective channels was dependent upon bath ATP (1.5 mM) and increased upon exposure to cAMP-dependent protein kinase. The channels displayed a single substate, located just below 2/3 of the full channel amplitude. Halide selectivity was identified as PBr > PI > PCl from the Goldman equation; however, the conductance sequence when either halide was permeating the channel was GCl > GBr >> GI. In inside-out patches, the channels were blocked reversibly by 5-nitro-2-(3-phenylpropylamino)benzoic acid, glibenclamide, and diphenylamine-2-carboxylic acid, whereas 4, 4-diisothiocyanatostilbene-2,2-disulfonic acid blocked channel activity completely and irreversibly. Single-channel kinetics revealed one open state (mean lifetime = 158 +/- 72 ms) and two closed states (lifetimes: 12 +/- 4 and 224 +/- 31 ms, respectively). Power density spectra had a double-Lorentzian form with corner frequencies 0.85 +/- 0.11 and 27.9 +/- 2.9 Hz, respectively. These channels are considered homologous to the cystic fibrosis transmembrane conductance regulator Cl- channel, which has been localized to the submucosal skin glands in Xenopus by immunohistochemistry (Engelhardt, J.F., S.S. Smith, E. Allen, J.R. Yankaskas, D.C. Dawson, and J.M. Wilson. 1994. Am. J. Physiol. 267: C491-C500) and, when stimulated by cAMP-dependent phosphorylation, are suggested to function in chloride secretion.
食用蛙（食用蛙）皮肤外分泌腺腺泡腔膜中的氯离子通道构成了一个单一的同质群体。在细胞贴附片中，通道在暴露于异丙肾上腺素、福斯可林或二丁酰环磷腺苷以及异丁基-1-甲基黄嘌呤时被激活，并向外整流，外向电流的电导为10.0±0.4 pS。受刺激细胞中的通道在施加0 mV电位时反转，而未受刺激细胞中的通道在去极化电位（28.1±6.7 mV）时反转，这表明在未受刺激而非受刺激的细胞中，Cl-高于电化学平衡。在内部面向外的膜片中，内部含有25 mM Cl-，小的（8 pS）线性Cl-选择性通道的活性依赖于浴中的ATP（1.5 mM），并且在暴露于cAMP依赖性蛋白激酶时增加。这些通道显示出一个单一的亚状态，位于全通道幅度的2/3以下。根据戈德曼方程，卤化物选择性被确定为PBr>PI>PCl；然而，当任何一种卤化物通透通道时，电导顺序为GCl>GBr>>GI。在内部面向外的膜片中，通道被5-硝基-2-（3-苯丙基氨基）苯甲酸、格列本脲和二苯胺-2-羧酸可逆性阻断，而4,4-二异硫氰酸根合芪-2,2-二磺酸完全不可逆地阻断通道活性。单通道动力学揭示了一个开放状态（平均寿命=158±72 ms）和两个关闭状态（寿命分别为12±4和224±31 ms）。功率密度谱具有双洛伦兹形式，拐角频率分别为0.85±0.11和27.9±2.9 Hz。这些通道被认为与囊性纤维化跨膜电导调节因子Cl-通道同源，通过免疫组织化学已将其定位到非洲爪蟾的粘膜下皮肤腺体中（恩格尔哈特，J.F.，S.S.史密斯，E.艾伦，J.R.扬卡斯卡斯，D.C.道森，和J.M.威尔逊。1994。美国生理学杂志。267：C491-C500），并且当受到cAMP依赖性磷酸化刺激时，被认为在氯离子分泌中起作用。
