Johnsen A H, Nielsen R
Gen Comp Endocrinol. 1984 Apr;54(1):144-53. doi: 10.1016/0016-6480(84)90210-7.
The cAMP level in isolated frog skin epithelia was stimulated by a range of concentrations of the antidiuretic hormone arginine vasotocin (AVT) and compared to active sodium transport measured as short-circuit current (SCC). The response of SCC and osmotic water flow (OWF) to AVT was investigated in a separate series. SCC was approximately three times more sensitive to AVT than OWF. Measurable increments of cAMP above the basal level were found only with AVT concentrations eliciting half-maximal response or more of SCC. Two models are offered to explain the findings: (A) Total SCC depends on epithelial cAMP with a sigmoidal relationship. (B) Epithelial cAMP exists in two separate pools of which only one is accessible to AVT, and SCC stimulation depends on cAMP in the AVT-controlled pool in a simple saturable fashion. Correlation between cAMP and SCC after stimulation with theophylline resembled that after AVT. Papaverine (10 microM) induced only small changes in SCC inspite of a substantial increase in cAMP level. Higher concentrations of papaverine inhibited both basal and AVT-stimulated SCC, while the cAMP level was further increased. This effect of papaverine may be due to a simultaneous block of another rate-determining process. Papaverine had no effect on basal or AVT-stimulated OWF despite a marked stimulation of the cAMP level. Thus, the role of cAMP as mediator of the hydroosmotic action of AVT must be questioned.
离体蛙皮上皮细胞中的环磷酸腺苷（cAMP）水平受到一系列浓度的抗利尿激素精氨酸血管加压素（AVT）刺激，并与以短路电流（SCC）衡量的活性钠转运进行比较。在另一组实验中研究了SCC和渗透水流量（OWF）对AVT的反应。SCC对AVT的敏感性约为OWF的三倍。仅在引起SCC半数最大反应或更大反应的AVT浓度下，才发现cAMP高于基础水平的可测量增加。提出了两种模型来解释这些发现：（A）总SCC取决于上皮细胞cAMP，呈S形关系。（B）上皮细胞cAMP存在于两个独立的池中，其中只有一个池可被AVT作用，SCC刺激以简单的饱和方式取决于AVT控制池中的cAMP。用茶碱刺激后cAMP与SCC之间的相关性类似于AVT刺激后的相关性。尽管cAMP水平大幅升高，但罂粟碱（10 microM）仅引起SCC的微小变化。更高浓度的罂粟碱抑制基础和AVT刺激的SCC，而cAMP水平进一步升高。罂粟碱的这种作用可能是由于同时阻断了另一个限速过程。尽管cAMP水平明显升高，但罂粟碱对基础或AVT刺激的OWF没有影响。因此，cAMP作为AVT水渗透作用介质的作用必须受到质疑。
