Question

In the proximal tubule, hydrogen ions are transported into the filtrate by ________.

1) Na⁺/H+ countertransporters only
2) H+ primary active transporters only
3) H+/Cl⁻ cotransporters only
4) both Na⁺/H+ countertransporters and H+ primary active transporters
5) both Na⁺/H+ countertransporters and H+/Cl⁻ cotransporters

Answer 1

In the proximal tubule, hydrogen ions are transported into the filtrate by both Na+/H+ countertransporters and H+ primary active transporters, contributing to acid-base balance and bicarbonate conservation.

Step-by-step explanation:

In the proximal tubule of the nephron, hydrogen ions (H+) are transported into the filtrate via both Na+/H+ countertransporters and H+ primary active transporters. Sodium ions (Na+) are reabsorbed from the filtrate in exchange for hydrogen ions by an antiport mechanism in the apical membranes of cells lining the renal tubule (Na+/H+ countertransport). Concurrently, H+ ions may also be secreted into the filtrate using H+ primary active transporters that do not depend on the Na+ gradient. Together, these processes contribute to acid-base balance by conserving bicarbonate ions (HCO3−) and excreting H+ ions.