Which one of the following is NOT involved in the secretion of K⁺ from blood into the tubular fluid by the principal cells of distal tubules?

Correct option is C

Correct Answer: Option 3
Explanation: In principal cells of the distal tubule and collecting duct, K⁺ secretion occurs mainly through ROMK and BK channels present on the apical membrane. K⁺/Cl⁻ cotransporters (KCC1) help maintain intracellular ionic balance indirectly supporting K⁺ handling. The Na⁺–K⁺–2Cl⁻ symporter (NKCC2) is located in the thick ascending limb of the loop of Henle, not in principal cells of the distal tubule. Therefore, it is not involved in K⁺ secretion by principal cells.