Various solutes are reabsorbed in the proximal tubule during tubular reabsorption. Which of the following ion is exchanged for H+ in proximal convoluted tubule?

Na+/H+ exchanger (NHE3) is located in the luminal membrane of the proximal tubule epithelial cell. This transpo system allows Na+ to enter the cell from the tubular lumen in exchange for a proton (H+) from inside the cell. As in all poions of the nephron, Na+/K+-ATPase in the basolateral membrane pumps the reabsorbed Na+ into the interstitium so as to maintain a low intracellular Na+ concentration. The H+ secreted into the lumen combines with bicarbonate (HCO3-) to form H2CO3 (carbonic acid). Ref: Ives H.E. (2012). Chapter 15. Diuretic Agents. In B.G. Katzung, S.B. Masters, A.J. Trevor (Eds), Basic & Clinical Pharmacology, 12e.