Final answer:
The target of muscarinic receptor antagonists in parietal cells is the gastric mucosa.
Step-by-step explanation:
The target of muscarinic receptor antagonists in parietal cells is the gastric mucosa. Parietal cells are found in the stomach and are responsible for producing hydrochloric acid required for digestion. Muscarinic receptor antagonists block the action of acetylcholine on the parietal cells, reducing acid secretion.