1 Danish Biomembrane Research Centre, Faculty of Health Sciences, Aarhus University, Aarhus University2 Department of Physiology and Biophysics, Faculty of Health Sciences, Aarhus University, Aarhus University3 Aarhus Institute of Advanced Studies, Centers at the university level, Aarhus University4 Department of Biomedicine - Forskning og uddannelse, Vest, Department of Biomedicine, Health, Aarhus University5 Aarhus Institute of Advanced Studies, Centers at the university level, Aarhus University6 Department of Biomedicine - Forskning og uddannelse, Vest, Department of Biomedicine, Health, Aarhus University
Homeostatic control of plasma K+ is a necessary physiological function. The daily dietary K+ intake of approximately 100 mmol is excreted predominantly by the distal tubules of the kidney. About 10% of the ingested K+ is excreted via the intestine. K+ handling in both organs is specifically regulated by hormones and adapts readily to changes in dietary K+ intake, aldosterone and multiple local paracrine agonists. In chronic renal insufficiency, colonic K+ secretion is greatly enhanced and becomes an important accessory K+ excretory pathway. During severe diarrheal diseases of different causes, intestinal K+ losses caused by activated ion secretion may become life threatening. This topical review provides an update of the molecular mechanisms and the regulation of mammalian colonic K+ absorption and secretion. It is motivated by recent results, which have identified the K+ secretory ion channel in the apical membrane of distal colonic enterocytes. The directed focus therefore covers the role of the apical Ca2+ and cAMP-activated BK channel (KCa1.1) as the apparently only secretory K+ channel in the distal colon.