Study of relationship between intracellular signal transduction system and bile secretion

在分离的大鼠肝细胞中，加压素的加入导致肌醇三磷酸的形成和细胞内Ca^<2+>浓度的增加（[Ca^<2+>]c）呈剂量依赖性。在肝脏灌注实验中，输注抗利尿激素引起胆汁分泌一过性增加而明显减少，导致胆汁淤积。抗利尿激素治疗后，辣根过氧化物酶（HRP）进入胆汁的流量呈剂量依赖性增加。这些数据表明，[Ca^<2+>]c的增加诱导了胆汁淤积，但增强了大鼠肝细胞的囊泡运输。用cAMP类似物激活蛋白激酶A可明显增强抗利尿激素诱导的离体肝细胞[Ca^<2+>]c升高。cAMP类似物增加灌注肝的胆汁分泌。然而，cAMP类似物治疗引起短暂性增加和随后的胆汁分泌减少的显着增强。低浓度加压素（10pM）的加入不影响[Ca^<2+>]c和胆汁分泌，但cAMP类似物治疗后可观察到[Ca^<2+>]c升高和胆汁分泌减少，提示[Ca^<2+>]c升高与胆汁淤积密切相关。然而，牛磺酸脱氧胆酸盐（TUDCA）阻止了cAMP类似物对[Ca^<2+>]c升高和胆汁淤积的增强作用。此外，TUDCA还能抑制胰高血糖素对蛋白激酶A的激活。这些数据表明，TUDCA可能作为蛋白激酶a的抑制剂。

In isolated rat hepatocytes, addition of vasopressin causes the inositol trisphosphate formation and increase of intracellular Ca^<2+> concentration ([Ca^<2+>]c) in a dose dependent manner. In the experiments with perfused liver, infusion of vasopressin caused transient increase and prominent decrease in bile secretion, resulting in cholestasis. Flow of horseradish peroxidase (HRP) into the bile increased by the treatment with vasopressin in a dose dependent manner. These data indicate that increase of [Ca^<2+>]c induces cholestasis, but enhances vesicle transport in rat hepatocytes.Protein kinase A activation by the treatment with cAMP analog clearly enhanced vasopressin induced [Ca^<2+>]c increase in isolated hepatocytes. cAMP analog increased bile secretion in perfused liver. However, treatment with cAMP analog caused a marked enhancement in transient increase and the subsequent decrease of bile secretion. Addition of low concentration of vasopressin (10pM) does not affect [Ca^<2+>]c and bile secretion, but increase of [Ca^<2+>]c and decrease of bile secretion were observed by the treatment with cAMP analog, suggesting the close relationship between [Ca^<2+>]c increase and cholestasis. However, tauroursodeoxycholate (TUDCA) prevented the enhancement effect of cAMP analog on [Ca^<2+>]c increase and cholestasis. In addition, TUDCA inhibits the activation of protein kinase A by glucagon. These data indicate that TUDCA may act as a inhibitory agent of protein kinase A.