Effect of calcium on the H+/K+ ATPase of hog gastric microsomes.
The K+-stimulated, ouabain-insensitive ATPase activity present in vesicles of microsomal fractions from hog gastric mucosa can be demonstrated in fresh preparations by adding Ca2+ (micron range) to the incubation medium. Ca2+ effect is similar but not additive to the effect of gramicidin or freezing. High Ca2+ concentrations (1 mM) produce an inhibitory effect on the K+-stimulated ATPase activity. This effect is not seen in the presence of gramicidin. Calcium increases the magnitude of ATP-driven H+ uptake in vesicles exposed to K+ for periods of time up to 60 min. At longer times of exposure (120 min) the response does not differ from controls. It is concluded that Ca2+ at low concentrations (micron range) enhances the K+ permeability of the vesicular membrane. At higher concentrations (mM range), Ca2+ becomes inhibitory to the K+ permeability. A role for Ca2+ as a second messenger in stimulus-secretion coupling in the parietal cell is discussed.
D000818:Animals; D002118:Calcium / Q000494:pharmacology* / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D005753:Gastric Mucosa / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D006096:Gramicidin / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D008954:Models, Biological; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
D006096:Gramicidin; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium