Park M K, Lomax R B, Tepikin A V, Petersen O H
Medical Research Council Secretory Control Research Group, Physiological Laboratory, University of Liverpool, Liverpool L69 3BX, United Kingdom.
Proc Natl Acad Sci U S A. 2001 Sep 11;98(19):10948-53. doi: 10.1073/pnas.181353798. Epub 2001 Sep 4.
In exocrine acinar cells, Ca(2+)-activated Cl(-) channels in the apical membrane are essential for fluid secretion, but it is unclear whether such channels are important for Cl(-) uptake at the base. Whole-cell current recording, combined with local uncaging of caged Ca(2+), was used to reveal the Cl(-) channel distribution in mouse pancreatic acinar cells, where approximately 90% of the current activated by Ca(2+) in response to acetylcholine was carried by Cl(-). When caged Ca(2+) in the cytosol was uncaged locally in the apical pole, the Cl(-) current was activated, whereas local Ca(2+) uncaging in the basal or lateral areas of the cell had no effect. Even when Ca(2+) was uncaged along the whole inner surface of the basolateral membrane, no Cl(-) current was elicited. There was little current deactivation at a high cytosolic Ca(2+) concentration (Ca(2+)), but at a low Ca(2+) there was clear voltage-dependent deactivation, which increased with hyperpolarization. Functional Ca(2+)-activated Cl(-) channels are expressed exclusively in the apical membrane and channel opening is strictly regulated by Ca(2+) and membrane potential. Ca(2+)-activated Cl(-) channels do not mediate Cl(-) uptake at the base, but acetylcholine-elicited local Ca(2+) spiking in the apical pole can regulate fluid secretion by controlling the opening of these channels in the apical membrane.
在外分泌腺泡细胞中，顶膜上的Ca(2+)激活的Cl(-)通道对于液体分泌至关重要，但尚不清楚此类通道对基底侧的Cl(-)摄取是否重要。全细胞电流记录结合笼锁Ca(2+)的局部解笼锁，用于揭示小鼠胰腺腺泡细胞中Cl(-)通道的分布，其中约90%由乙酰胆碱引起的Ca(2+)激活电流由Cl(-)携带。当在细胞顶部极局部解笼锁胞质中的笼锁Ca(2+)时，Cl(-)电流被激活，而在细胞基底侧或侧面区域局部解笼锁Ca(2+)则无影响。即使沿着基底外侧膜的整个内表面解笼锁Ca(2+)，也不会引发Cl(-)电流。在高胞质Ca(2+)浓度(Ca(2+))下电流失活很少，但在低Ca(2+)时存在明显的电压依赖性失活，且随着超极化而增加。功能性Ca(2+)激活的Cl(-)通道仅在顶膜中表达，且通道开放严格受Ca(2+)和膜电位调节。Ca(2+)激活的Cl(-)通道不介导基底侧的Cl(-)摄取，但乙酰胆碱引发的细胞顶部极局部Ca(2+)尖峰可通过控制顶膜中这些通道的开放来调节液体分泌。
