GUINEA-PIG 5-HT TRANSPORTER - CLONING, EXPRESSION, DISTRIBUTION, AND FUNCTION IN INTESTINAL SENSORY RECEPTION

Studies of the guinea pig small intestine have suggested that serotoni n (5-HT) may be a mucosal transmitter that stimulates sensory nerves a nd initiates peristaltic and secretory reflexes. We tested the hypothe sis that guinea pig villus epithelial cells are able to inactivate 5-H T because they express the same 5-HT transporter as serotonergic neuro ns. A full-length cDNA, encoding a 630-amino acid protein (89.2% and 9 0% identical, respectively, to the rat and human 5-HT transporters) wa s cloned from the guinea pig intestinal mucosa. Evidence demonstrating that this cDNA encodes the guinea pig 5-HT transporter included 1) hy bridization with a single species of mRNA (similar to 3.7 kb) in North ern blots of the guinea pig brain stem and mucosa and 2) uptake of [H- 3]5-HT by transfected HeLa cells via a saturable, high-affinity (Micha elis 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 epith elium of the entire crypt-villus axis was demonstrated by in situ hybr idization and immunocytochemistry. Inhibition of mucosal 5-HT uptake p otentiates responses of submucosal neurons to mucosal stimulation. The epithelial reuptake of 5-HT thus appears to be responsible for termin ating mucosal actions of 5-HT.