Functions of serotonin-containing EC cells in the GI tract

研究了含5-羟色胺（5-HT）的肠嗜铬细胞在胃肠道中的功能作用。首先，我们研究了离体灌流大鼠十二指肠5-HT释放的调节机制。胆碱能毒蕈碱机制刺激5 HT释放到肠腔。CCK刺激5 HT释放到管腔内，其机制是通过胆碱能机制介导的。VIP和PACAP可通过VIP-2受体抑制5-HT向EC释放。VIP/PACAPs和NO对5-HT释放的抑制作用密切相关。为了检测EC细胞释放的5 HT的功能作用，研究了5 HT受体拮抗剂对肠运动的影响。5 HT-3受体拮抗剂可明显阻断十二指肠运动。5 HT-4受体拮抗剂每周阻断运动，而5 HT-1或-2受体拮抗剂不改变运动。最后，我们通过免疫电镜检查了刺激管腔释放5 HT后5 HT细胞内定位的变化。由于我们获得了高管腔内压刺激管腔内5 HT释放的证据，因此将离体灌流的十二指肠暴露于高管腔内压，固定并制备用于免疫电镜研究。在正常情况下，与5-HT反应的免疫金颗粒集中在分泌颗粒上，而在刺激的十二指肠中，它们弥散地散布在颗粒外细胞质和微绒毛上。这些结果表明，5-HT可能是由EC细胞通过一种双分泌方式向肠腔扩散释放的。

The functional role of serotonin (5HT)-containing enterochromaffin cells in the gastrointestinal tract has been studied. First of all, we examined the mechanism to regulate the release of 5HT from isolated perfused rat duodenum. Cholinergic muscarinic mechanism stimulated the release of 5HT into the intestinal lumen. CCK stimulated the release of 5HT into the lumen, this mechanism was mediated by the cholinergic mechanism. VIP and PACAP inhibited the release of 5HT into the lumen via the VIP-2 receptors on the EC cells. VIP/PACAPs and NO were strongly related on the inhibition of 5HT release. To examine the functional role of 5HT released from the EC cells, the effect of 5HT receptor antagonists on the intestinal motility was investigated. 5HT-3 receptor antagonist strongly blocked the duodenal motility. 5HT-4 receptor antagonist weekly blocked, however 5HT-1 or-2 receptor antagonist did not change the motility. Finally, we examined the change in the intracellular localization of 5HT after stimulation of luminal release of 5HT by immunoelectron microscopy. Since we obtained the evidence that the luminal release of 5HT was stimulated by the high intraluminal pressure, the isolated perfused duodenum was exposed to the high luminal pressure, fixed and prepared for immunoelectron microscopic study. Immunogold particles which react to 5HT were concentrated over the secretory granules in normal conditions, however they diffusely scattered over the extragranular cytoplasm and over the microvilli in the stimulated duodenum. These results suggest that 5HT might be diffusely released from the EC cells to the intestinal lumen by a diacrine manner of secretion.