[Molecular biology of transporters in GI tracts]

The transporters and channels expressed in gastrointestinal tracts were reviewed. The transporters at the apical membrane are coupled with sodium, chloride or hydrogen ions and elecrogenic to accumulate substrates actively against concentration gradient. The transporters at the basolateral membrane are usually facilitators. They belong to several membrane protein families. Their members are increasing with homology cloning. The new families are found with expression cloning and genome sequencing. The posttranscriptional modulation and accesory proteins may regulate the activity of transporters. The mechanisms of tissue specific expression and gene expression are actively investigated.