Cation effects on acid secretion in rabbit gastric glands

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Abstract
The ability of isolated gastric glands to produce acid as a function of intra- and extracellular concentrations of K+ and Na+ was investigated. Ouabain inhibited acid formation as measured by the aminopyrine (AP) accumulation technique in a dose-dependent manner with an ED50 of 2 .times. 10-6 M at 5.4 mM extracellular K+. This inhibition was counteracted by increasing extracellular K+ or decreasing extracellular Na+. In K+-free solutions with regular Na+, the AP accumulation was almost totally abolished; the readdition of K+ rapidly restored the response with a K0.5 of 1 mM extracellular K+. In the absence of Na+, with or without ouabain, there was always a significant residual AP accumulation, but the K0.5 of extracellular K+ required for acid formation increased to .apprx. 20 mM. Despite repeated washings in Na+-K+-free solutions, the the intracellular K+ content could not be decreased below 24 mM above the apparent K0.5 for K+. The intracellular K+ could be depleted without disturbance of the acid secretory function if the glands were treated with the neutral ionophore amphotericin B and ouabain in K+-Na+-free solutions. Complete dose-response curves of H+ secretion as a function of K+ concentration could now be obtained. Thus the K0.5 for K+ activation of AP accumulation was 16.5 .+-. 0.9 mM; upon histamine stimulation of the glands, the K0.5 decreased to 10.4 .+-. 0.7 mM. Intracellular K+ concentrations above .apprx. 60 mM inhibited AP accumulation. Na+ dose dependently inhibited the K+-induced response. At low extracellular K+ concentrations, a ouabain-insensitive K+ accumulation mechanism was unmasked. This K+ uptake was partly inhibited by p-chloromercuribenzene sulfonic acid and by inhibitors of the gastric H+-K+-ATPase and amplified by inhibitors of K+ conductance channels such as Ba2+. The K+ content of gastric glands is mainly regulated by the Na+-K+-ATPase, but additional K+-uptake pathways are present. The affinity for K+ is increased in histamine-stimulated glands, which might indicate one mechanism of stimulating the secretory response. Na+ inhibits secretion possibly by binding to the cytosolic cation site of the gastric ATPase. The cation relationship to acid secretion in the rabbit parietal cell is similar to that described for vesicles isolated from hog gastric mucosa.

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