CALCIUM-TRANSPORT AND CALCIUM-ACTIVATED ATPASE ACTIVITY IN MICROSOMALVESICLES OF RAT GASTRIC-MUCOSA

1. Microsomal and plasma membrane vesicles, isolated from rat gastric mucosa, were found to exhibit Ca2+-dependent ATPase activities of 14.1 +/-1.4 and 7.8+/-1.1 mu mol/mg/hr, respectively. The optimum condition s for the microsomal Ca2+-ATPase was pH 6-7, and required Mg2+, while divalent cation such as CU2+, Zn2+, Fe2+, Ba2+ and Cd2+ had no signifi cant effect. 2. As in the case of Ca2+, Mg2+-ATPase, the Ca2+ uptake a ctivity of the microsomal membrane required Mg2+. Both processes were stimulated by submicro molar concentrations of Ca2+ and the apparent X , for Ca2+, Mg2+ ATPase and Ca2+ uptake activities were 0.06 mu M and 0.02 mu M, respectively. 3. Divalent cations Ba2+ and Fe2+, inhibited both microsomal activities, while Zn2+ and Cd2+ showed no effect on th em. However, the monovalent cation K+ did not stimulate Ca2+, Mg2+-ATP ase and Ca2+ uptake activities. 4. The Ca2+ pumping ATPase of rat gast ric mucosal microsome cross-reacted with a monoclonal antibody (mAb-5F 10) against the human erythrocyte Ca2+ pump. The apparent molecular we ight of mucosal Ca2+ pump was 98 kDa. 5. Close relationship between th e kinetic parameters of Ca2+, Mg2+-ATPase and Ca2+ uptake activities, and the cross reaction of 98 kDa protein of mucosal microsome with ery throcyte Ca2+ pump antibody, strongly suggest the expression of Ca2+ p ump in rat gastric mucosa.