Biochemical and cytochemical comparison of intestinal bicarbonate-stimulated Mg2+ dependent ATPase and alkaline phosphatase activities in rat, rabbit and guinea pig.

Bicarbonate-stimulated Mg2+ dependent ATPase activity was demonstrated both biochemically and cytochemically, in brush border membranes from rat, rabbit and guinea pig duodenum. There was no correlation between enzyme activity and basal HCO3- secretion rates in the different species. The concentration of HCO3- necessary for optimal stimulation of ATPase activity, degree of stimulation and total activity was higher in the rat than in other species. Activity was higher in rat duodenum than in the ileum. This is consistent with the proposed electrogenic HCO3- secretion in the duodenum. Distribution of activities of alkaline phosphatase and HCO3(-)-stimulated Mg2+-ATPase along the duodenal villus showed significant differences, suggesting that the two activities reflect, at least in part, distinct enzymes.