Histochemical distribution of potassium-dependent p-nitrophenylphosphatase in the calf intestine

Potassium-dependent p-nitrophenylphosphatase was demonstrated, using the lead citrate method of Mayahara et al. (1980), in frozen sections of calf intestine fixed in formalin-calcium. The calcium chloride included in the fixative was shown to improve the localization of the reaction markedly. The phosphatase activity observed in the basolateral cell borders of the surface epithelium in the small intestine and colon was reduced by 10 mM ouabain and by substitution of sodium ions for potassium ions, confirming that the reaction was representative for the second step in the Na+/K+-ATPase complex. The intensity of the basolateral enzyme reaction was in the order: colon greater than duodenum, proximal jejunum greater than ileum greater than middle and distal jejunum. The crypts reacted weakly. A reaction in the brush border of the proximal jejunum and duodenum and a granular reaction in the supranuclear cytoplasm of the epithelial cells was not influenced by ouabain. The staining pattern for the potassium-dependent phosphatase differed from that of alkaline phosphatase and Mg2+-dependent ATPase, which gave a reaction that was restricted to the brush border.