Figure 3.

Influence of aldosterone on K⁺ transport along the gastrointestinal tract. K⁺ absorption in the small bowel is primarily passive pulled by bulk water movement via solvent drag. K⁺ secretion in the colon occurs by both a passive and active mechanism, both of which are stimulated by aldosterone. Aldosterone does not affect the small component of active K⁺ absorption mediated by the apically located H⁺-K⁺-ATPase present in the terminal part of the colon. See text for discussion. Red indicates energy requiring transporter. BK, large-conductance, Ca²⁺-activated K(Ca)1.1 (BK) channel; NKCC, Na⁺-K⁺-2Cl^– cotransporter; ClC-2, chloride channel; ENaC, epithelial Na⁺ channel.