Category: biosynthesis
Parietal cells secrete HCl via the H+/K+-ATPase (proton pump) on the apical canalicular membrane. Three converging stimuli ramp the pump's activity: histamine (H2R, Gs → cAMP), acetylcholine (M3R, Gq → IP3 → Ca²⁺), gastrin (CCK2R, Gq). PPIs (omeprazole, pantoprazole, esomeprazole, lansoprazole, dexlansoprazole, rabeprazole) are acid-activated prodrugs that covalently inactivate the proton pump cysteine; effect outlasts plasma exposure. H2 blockers (famotidine, ranitidine — withdrawn 2020 for NDMA contamination, but slug retained) compete at H2R. M3 antagonists no longer used (broad anticholinergic side effects). Misoprostol is a PGE1 analog → mucosal cytoprotection + acid suppression; abortifacient at higher doses.