Characterization of gastric Na+/I- symporter of the rat

Characterization of gastric Na+/I- symporter (NIS) of the rat was carried o ut. Sequencing of the open reading frame of gastric MS mRNA showed only thr ee nucleotide changes when compared with FRTL-5 NIS cDNA, and two of these changes led to amino acid changes. The results of Northern blot analysis sh owed that abundant NIS mRNA was expressed in the stomach when compared with other organs. Western blot analysis using gastric mucosa and FRTL-5 lysate s detected the difference in molecular weight between FRTL-5 and gastric mu cosa lysates, suggesting abnormal posttranslational modification of gastric MS protein. Immunohistochemically, gastric MS protein was located in the c ornification layer of the stratified squamous epithelium of the pars proven tricularis and in parietal cells and on the apical border of surface epithe lial cells of the pars glandularis. Gastric MS protein was present in tubul ovesicular structures and lysosomes in parietal cells by immunoelectron mic roscopy. Gastric MS protein exists to trap I- from the gastric lumen, excep t in parietal cells. Results indicated that a very large amount of gastric MS mRNA is expressed to be translated, whereas only a small amount of immat ure gastric NIS protein is detected. This may indicate that immature gastri c MS protein rapidly degrades to peptides. (C) 1998 Academic Press.