This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T., Subject name: Physiology
Apical membrane of parietal cells contains which ion channels- 
Select and explain. 
A. Na+ K+ ATPase, B. H+ K+ ATPase, C. Na+ K+ 2Cl- transporter, D. Na+ - Ca+2 cotransporter
B: H+ K+ ATPase
Answer: B: H+ K+ ATPase 
Explanation: Ans. is 'b' i.e., H+ K+ ATPase o The H~ are produced inside the parietal cell through the reaction of metabolic CO., with water. The reaction is catalyzed by carbonic anhydrase. H+ is secreted by proton pump (H~ K'ATPase) into the gastric lumen in exchange with a K+ ion and the HCG, is transported out of the parietal cells at the basolateral membrane (by HCO3 - Cl- antiport ) into the interstitial fluid and from there into the blood. This HCO3- increases the blood pH. Hence after a meal, there is a rise in blood pH which is called the post-prandial alkaline tide.o The Cl" that enter the parietal cell in exchange for HCO3 are secreted into the lumen. So, inside the gastric lumen secreted H+ and Cl- from hydrochloric acid (HC1).