In proximal convoluted tubule, H+ is exchanged for?

The cells of the proximal and distal tubules, like the cells of the gastric glands, secrete hydrogen ions. Acidification also occurs in the collecting ducts. The reaction that is primarily responsible for H+ secretion in the proximal tubules is Na-H exchange. This is an example of secondary active transpo. Ref: Ganong's Review of Medical Physiology, 23rd edition, page no: 679 Ref of image :