Fig. 9.

Proposed mechanism of benzamil-induced Cl⁻ secretion. The Na-K-2Cl cotransporter, NKCC1, mediates Cl⁻ uptake across the basolateral membrane in type A intercalated cells. Cl⁻ is then secreted across the apical plasma membrane through a yet to be identified pathway. H⁺ is secreted by type A cells through the apical H⁺-ATPase, which is associated with Cl⁻ secretion mediated by this pathway. However, there is evidence that NKCC1 localizes to the basolateral regions of not only type A intercalated cells (14, 20), but also to the basolateral regions of principal cells (14).