Extracellular potassium is necessary for acid translocation but not for acid formation in gastric mucosa.
Removal of potassium from the nutrient solution of a gastric mucosa results in monotonic decline in acid secretion rate. When potassium is added back to the nutrient solution, acid secretion recovers. In both spontaneously and sub-maximally secreting tissue the recovery of the acid secretion rate takes the form of a transient overshoot above the baseline such that the amount of suppressed acid in the absence of potassium is equal to the amount of acid that is secreted above baseline once potassium is added back. The index of conservation r is zero, i.e., the effect is conservative. In maximally secreting tissue the secretion rate only returns to pre-inhibitory level without an overshoot. The net effect is nonconservative with r = -1. Conservative effect under maximally stimulating conditions was unmasked by exposing the tissue to a stimulus for a specific length of time and comparing amount of acid secreted when nutrient potassium was present with amount of acid secreted when potassium was removed and then added back to the nutrient solution. Stimulation with forskolin is not expressed in the absence of potassium but is unmasked once potassium is added back to the nutrient solution. The conclusion is: removing potassium from the nutrient side inhibits proton translocation by decreasing Vmax and/or increasing Km but is without effect on the formation of acid. Adding potassium back restores the parameter(s) for the translocation step.
Ekblad
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EB
Cardiovascular Research Institute, University of California, San Francisco 94143.
Licko
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D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D005744:Gastric Acid / Q000378:metabolism*; D005753:Gastric Mucosa / Q000378:metabolism*; D005768:Gastrointestinal Hormones / Q000378:metabolism; D017506:H(+)-K(+)-Exchanging ATPase; D066298:In Vitro Techniques; D011188:Potassium / Q000494:pharmacology*; D011898:Ranidae; D012636:Secretory Rate / Q000187:drug effects; D013223:Statistics as Topic
D005768:Gastrointestinal Hormones; C052257:hydrogen potassium ATPase, gastric endogenous activator protein, mammal; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium