Abstract
1.1. 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 μmol/mg/hr, respectively. The optimum conditions 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 significant effect.2.2. As in the case of Ca2+, Mg2+-ATPase, the Ca2+ uptake activity of the microsomal membrane required Mg2+. Both processes were stimulated by submicro molar concentrations of Ca2+ and the apparent Km for Ca2+, Mg2+ ATPase and Ca2+ uptake activities were 0.06 μM and 0.02 μM, respectively.3.3. Divalent cations Ba2+ and Fe2+, inhibited both microsomal activities, while Zn2+ and Cd2+ showed no effect on them. However, the monovalent cation K+ did not stimulate Ca2+, Mg2+-ATPase and Ca2+ uptake activities.4.4. The Ca2+ pumping ATPase of rat gastric mucosal microsome cross-reacted with a monoclonal antibody (mAb-5F10) against the human erythrocyte Ca2+ pump. The apparent molecular weight of mucosal Ca2+ pump was 98 kDa.5.5. Close relationship between the kinetic parameters of Ca2+, Mg2+-ATPase and Ca2+ uptake activities, and the cross reaction of 98 kDa protein of mucosal microsome with erythrocyte Ca2+ pump antibody, strongly suggest the expression of Ca2+ pump in rat gastric mucosa.
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