The distribution of K + -ATPase activity in surface and crypt cells from rabbit distal colon was studied. Separation of surface and crypt cells was validated using the multidrug resistance gene (mdr I) product. P-glycoprotein, as marker for differentiated surface epithelial cells. Western blot analysis revealed a 6-fold higher expression level of P-glycoprotein in colonic surface cells. K + -stimulated ouabain-insensitive ATPase activity was present in surface and in crypt cells. In surface cells, this K + -ATPase activity was only partly inhibitable by 10 μM SCH 28080, while in crypt cells K + -ATPase activity equalled SCH 28080-sensitive ATPase activity. These results strongly suggest the presence of two distinct K + -ATPases in colonic epithetial cells.