Question

Omeprazole produces antacid action by inhibiting

• A. H1 receptor
• B. H2 receptor
• C. H+ - K+ ATPase
• D. Na+ - K+ ATPase

Hint:

Gastric Acid Inhibitors:
Proton Pump Inhibitors (Omeprazole, Pantoprazole) $\rightarrow$ Irreversibly blocks $\text{H}^+/\text{K}^+$-ATPase.
$\text{H}_2$-Blockers (Ranitidine, Famotidine) $\rightarrow$ Blocks histamine $\text{H}_2$ receptors.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Proton pump inhibitors (PPIs) irreversibly inhibit the gastric parietal cell $ ext{H}^+/ ext{K}^+$-ATPase pump (the final common pathway of gastric acid secretion).
Key Formula or Approach:
\[ \text{Omeprazole (Sulfenamide active form)} + \text{Cys-813 of } \text{H}^+/\text{K}^+\text{-ATPase} \longrightarrow \text{Irreversible Covalent Disulfide Bond} \]

Step 2: Detailed Explanation:
Mechanism of action of Omeprazole (Proton Pump Inhibitor PPI):
- Omeprazole is a substituted benzimidazole prodrug that concentrates selectively in the acidic secretory canaliculi of gastric parietal cells ($pH < 2$).
- In the acidic environment, it undergoes proton-catalyzed rearrangement into an active thiophilic sulfenamide.
- The sulfenamide forms a covalent disulfide bond with critical cysteine residues (Cys813) of the $\text{H^+ - \text{K}^+$ ATPase (Gastric Proton Pump)}, permanently inactivating the enzyme and completely blocking basal and stimulated gastric hydrochloric acid secretion.

Step 3: Final Answer:
Therefore, Omeprazole acts by inhibiting H+ - K+ ATPase, matching option (C).