BK channels in the kidney: Role in K⁺ secretion and localization of molecular components

Although it is generally accepted that ROMK is the K⁺ secretory channel in the mammalian distal nephron, recent in vitro and in vivo studies have provided evidence that large-conductance Ca²⁺-activated K ⁺ channels (BK, or maxi K) also secrete K⁺ in renal tubules. This review assesses the current evidence relating BK channels with K⁺ secretion. We shall consider the component proteins of the BK channel, their localization with respect to segment and cell type, and the electrophysiological forces involved in K⁺ secretion. Although the majority of studies have focused on a role for BK channels in flow-mediated K⁺ secretion, this review also considers a potential role for BK channels in high-K diet-induced K⁺ secretion. The division of workload between ROMK and BK is discussed as a mechanism for ensuring a constant plasma K⁺ concentration.