POTASSIUM-STIMULATED ATPASE ACTIVITY AND HYDROGEN TRANSPORT IN GASTRIC MICROSOMAL VESICLES

The Mg2+-dependent, K+-stimulated ATPase of microsomes from pig gastric mucosa has been studied in relation to observed active H+ transport into vesicular space. Uptake of fluorescent dyes (acridine orange and 9-aminoacridine) was used to monitor the generated pH gradient. Freeze-fracture electron microscopy showed that the vesicular gastric microsomes have an asymmetric distribution of intramembraneous particles (P-face was particulate; E-face was relatively smooth). Valinomycin stimulated both dye uptake and K+-ATPase (valinomycin-stimulated K+-ATPase); stimulation by valinomycin was due to increased K+ entry to some intravesicular activating site, which in turn depends upon the accompanying anion. Using the valinomycin-stimulated K+-ATPase and H+ accumulation as an index, the sequence for anion permeation was NO3- > Br- > Cl- > I- > acetate ≈ isethionate. When permeability to both K+ and H+ was increased (e.g using valinomycin plus a protonophore or nigericin), stimulation of K+-ATPase was much less dependent on the anion and the observed dissipation of the vesicular pH gradient was consistent with an 'uncoupling' of ATP hydrolysis from H+ accumulation. Thiocyanate interacts with valinomycin inhibiting the typical action of the K+ ionophore. But stimulation of ATPase activity was seen by adding 10 mM SCN- to membranes preincubated with valinomycin. From the relative activation of the valinomycin-stimulated K+-ATPase, it appears that SCN- is a very. © 1979.