Chen J X, Pan H, Rothman T P, Wade P R, Gershon M D
Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
Am J Physiol. 1998 Sep;275(3):G433-48. doi: 10.1152/ajpgi.1998.275.3.G433.
Studies of the guinea pig small intestine have suggested that serotonin (5-HT) may be a mucosal transmitter that stimulates sensory nerves and initiates peristaltic and secretory reflexes. We tested the hypothesis that guinea pig villus epithelial cells are able to inactivate 5-HT because they express the same 5-HT transporter as serotonergic neurons. A full-length cDNA, encoding a 630-amino acid protein (89.2% and 90% identical, respectively, to the rat and human 5-HT transporters) was cloned from the guinea pig intestinal mucosa. Evidence demonstrating that this cDNA encodes the guinea pig 5-HT transporter included 1) hybridization with a single species of mRNA ( approximately 3.7 kb) in Northern blots of the guinea pig brain stem and mucosa and 2) uptake of [3H]5-HT by transfected HeLa cells via a saturable, high-affinity (Michaelis constant 618 nM, maximum velocity 2.4 x 10(-17) mol . cell-1 . min-1), Na+-dependent mechanism that was inhibited by chlorimipramine > imipramine > fluoxetine > desipramine > zimelidine. Expression of the 5-HT transporter in guinea pig raphe and enteric neurons and the epithelium of the entire crypt-villus axis was demonstrated by in situ hybridization and immunocytochemistry. Inhibition of mucosal 5-HT uptake potentiates responses of submucosal neurons to mucosal stimulation. The epithelial reuptake of 5-HT thus appears to be responsible for terminating mucosal actions of 5-HT.
对豚鼠小肠的研究表明，血清素（5-羟色胺，5-HT）可能是一种刺激感觉神经并引发蠕动和分泌反射的黏膜递质。我们验证了这样一个假说，即豚鼠绒毛上皮细胞能够使5-HT失活，因为它们表达与血清素能神经元相同的5-HT转运体。从豚鼠肠黏膜中克隆出一个全长cDNA，其编码一种630个氨基酸的蛋白质（分别与大鼠和人类的5-HT转运体有89.2%和90%的同源性）。证明该cDNA编码豚鼠5-HT转运体的证据包括：1）在豚鼠脑干和黏膜的Northern印迹中与单一物种的mRNA（约3.7 kb）杂交；2）转染的HeLa细胞通过一种可饱和、高亲和力（米氏常数618 nM，最大速度2.4×10⁻¹⁷ mol·细胞⁻¹·分钟⁻¹）、依赖钠离子的机制摄取[³H]5-HT，该机制受氯米帕明>丙咪嗪>氟西汀>地昔帕明>齐美利定抑制。通过原位杂交和免疫细胞化学证明了5-HT转运体在豚鼠中缝核、肠神经元以及整个隐窝-绒毛轴上皮中的表达。抑制黏膜对5-HT的摄取会增强黏膜下神经元对黏膜刺激的反应。因此，5-HT的上皮再摄取似乎是终止5-HT黏膜作用的原因。
