Osteoclasts create a sealed resorption lacuna beneath the ruffled border and must acidify it to dissolve hydroxyapatite. Which transporter on the ruffled border membrane directly pumps protons into the lacuna?

• A Na+/H+ exchanger isoform 3
• B Na+/K+-ATPase
• C Vacuolar-type H+-ATPase ✓
• D Cl-/HCO3- exchanger

Explanation

The osteoclast ruffled border expresses a vacuolar-type H+-ATPase that actively secretes protons into the sealed lacuna, dropping its pH to about 4.5 and dissolving mineral. A chloride channel provides charge balance, and cytoplasmic carbonic anhydrase II supplies the protons. The Cl-/HCO3- exchanger sits on the opposite basolateral membrane to export bicarbonate, so it does not deliver acid to the lacuna.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.