ph-dependent, HCO-3-stimulated ATPase of rat jejunum

Mucosal homogenates from rat jejunum were tested for both HCO-3-stimulated ATPase and anion-stimulated, SCN-inhibited ATPase in assay mixtures ungassed, gassed with pure oxygen or gassed with the appropriate gaseous phase. Experiments were performed at four different initial pHs (7.15; 7.45; 8.10; 8.55) with or without the presence of Triton X-100. Assay mixtures were tested for both pH and % CO2. Only at pH 7.15 and 7.45 anion-sensitive ATPase activities in ungassed conditions are different from those in mixtures gassed with the proper gaseous phase. Moreover, at cited pHs in ungassed mixtures the final pH is higher and % CO2 is lower than initial values. Therefore it seems possible to obtain the exact determination of anion-sensitive ATPases at all pH values only from mixtures gassed with the proper gaseous phase. Bicarbonate-stimulated ATPase activity is absent both at pH 7.15 and 7.45; this fact seems to exclude, at these pHs, an active transport of bicarbonate directly depending on this enzyme activity.