View of K⁺ secretion through the apical K channel of cortical collecting duct

The apical small-conductance K⁺ channel plays an important role in renal K⁺ secretion, as evidenced by the presence of the extensive modulatory pathways. Stimulation of adenylate cyclase enhances channel activity and consequently K⁺ secretion. In contrast, increases in intracellular Ca²⁺ concentration and activation of Ca²⁺-dependent signal transduction pathways inhibit the K⁺ channel and thus decrease K⁺ secretion. The vasopressin-induced stimulation of K⁺ secretion in CCD results at least in part from cAMP-dependent signal transduction pathways. The Ca²⁺-dependent signal transduction pathway is responsible for modulatory coupling between Na⁺ pump turnover and apical K⁺ conductance when the Na⁺ pump is inhibited.