Which of the Following Normally Functions to Lower the PH

Question

Which of the following normally functions to lower the pH of the cytosol?
A) A Na⁺-H⁺ exchanger in the plasma membrane.
B) A Na⁺-driven Cl--HCO₃- exchanger in the plasma membrane.
C) A Na⁺-independent Cl--HCO₃-exchanger in the plasma membrane.
D) A V-type ATPase in the lysosomal membrane.
E) Both answers A and B above.

Accepted Answer

The Na⁺-H⁺ exchanger and the Na⁺-driven Cl--HCO₃- exchanger in the plasma membrane help pump out protons from the cytosol (increase the cytosolic pH), and the latter exchanger also neutralizes cytosolic protons by bringing in bicarbonate ions. On the other hand, the Na⁺-independent Cl--HCO₃-exchanger, which is activated at high pH, helps lower the pH by transporting bicarbonate ions out of the cell down their electrochemical gradient.