Dharmsathaphorn K, Pandol S J
J Clin Invest. 1986 Feb;77(2):348-54. doi: 10.1172/JCI112311.
Serosal application of carbachol to T84 cell monolayers mounted in an Ussing chamber caused an immediate increase in short circuit current (Isc) that peaked within 5 min and declined rapidly thereafter, although a small increase in Isc persisted for approximately 30 min. The increase in Isc was detectable with 1 microM carbachol; half-maximal with 10 microM carbachol; and maximal with 100 microM carbachol. Unidirectional Na+ and Cl- flux measurements indicated that the increase in Isc was due to net Cl- secretion. Carbachol did not alter cellular cAMP, but caused a transient increase in free cytosolic Ca2+ ([Ca2+]i) from 117 +/- 7 nM to 160 +/- 15 nM. The carbachol-induced increase in Isc was potentiated by either prostaglandin E1 (PGE1) or vasoactive intestinal polypeptide (VIP), agents that act by increasing cAMP. Measurements of cAMP and [Ca2+]i indicated that the potentiated response was not due to changes in these second messengers. Studies of the effects of these agents on ion transport pathways indicated that carbachol, PGE1, or VIP each increased basolateral K+ efflux by activating two different K+ transport pathways on the basolateral membrane. The pathway activated by carbachol was not sensitive to barium, while that activated by PGE1 or VIP was; furthermore, their action on K+ efflux are additive. Our study indicates that carbachol causes Cl- secretion, and that this action may result from its ability to increase [Ca2+]i and basolateral K+ efflux. Carbachol's effect on Cl- secretion is greatly augmented in the presence of VIP or PGE1, which open a cAMP-sensitive Cl- channel on the apical membrane, accounting for a potentiated response.
将卡巴胆碱应用于安装在尤斯灌流小室中的T84细胞单层，可使短路电流（Isc）立即增加，在5分钟内达到峰值，此后迅速下降，尽管Isc仍有小幅增加并持续约30分钟。1 μM卡巴胆碱可检测到Isc增加；10 μM卡巴胆碱时达到半最大效应；100 μM卡巴胆碱时达到最大效应。单向Na⁺和Cl⁻通量测量表明，Isc增加是由于净Cl⁻分泌。卡巴胆碱不会改变细胞内cAMP，但会使游离胞质Ca²⁺（[Ca²⁺]i）从117±7 nM短暂增加到160±15 nM。前列腺素E1（PGE1）或血管活性肠肽（VIP）可增强卡巴胆碱诱导的Isc增加，这两种物质通过增加cAMP起作用。cAMP和[Ca²⁺]i测量表明，增强的反应并非由于这些第二信使的变化。这些物质对离子转运途径影响的研究表明，卡巴胆碱、PGE1或VIP各自通过激活基底外侧膜上两种不同的K⁺转运途径来增加基底外侧K⁺外流。卡巴胆碱激活的途径对钡不敏感，而PGE1或VIP激活的途径对钡敏感；此外，它们对K⁺外流的作用是相加的。我们的研究表明，卡巴胆碱可引起Cl⁻分泌，且这种作用可能源于其增加[Ca²⁺]i和基底外侧K⁺外流的能力。在存在VIP或PGE1的情况下，卡巴胆碱对Cl⁻分泌的作用会大大增强，它们会在顶端膜上打开一个对cAMP敏感的Cl⁻通道，从而导致增强的反应。
