INTESTINAL AMMONIUM TRANSPORT BY AMMONIUM AND HYDROGEN-EXCHANGE

BACKGROUND: Ionized ammonia (NH3) transport in the intestine has not b een previously established as a mechanism of acidosis in urinary intes tinal diversion or hepatic failure. STUDY DESIGN: The purpose of this study was to establish that ionized transport of ammonium (NH4) occurs in the intestine and to characterize the mechanism of its transport u sing the methodology of brush border membrane vesicles and acridine or ange fluorescence. RESULTS: An NH4/H exchange was demonstrated and fou nd to be the dominant mechanism causing a pH change when NH4 is transp orted across the lumenal membrane. Ionized NH4 transport was demonstra ted to occur against an NH3 concentration gradient. The K-m was 1.02 m mol and the V-max was 247 U/sec. The Hill coefficient was 0.97, indica ting a single port. Ammonium hydrogen exchange could be inhibited by a miloride but not by bumetanide, Sodium, potassium or chloride, or both , did not effect the NH4/H exchanger. CONCLUSIONS: This study establis hes that ionized NH4 transport occurs across the small intestine brush border in exchange for a hydrogen ion.