Physiology and Pathophysiology of Potassium Channels in Gastrointestinal Epithelia

Institute of Physiology and Clinic and Policlinic for Internal Medicine II, Regensburg, Germany Epithelial cells of the gastrointestinal tract are an important barrier between the "milieu interne" and the luminal content of the gut. They perform transport of nutrients, salts, and water, which is essential for the maintenance of body homeostasis. In these epithelia, a variety of K + channels are expressed, allowing adaptation to different needs. This review provides an overview of the current literature that has led to a better understanding of the multifaceted function of gastrointestinal K + channels, thereby shedding light on pathophysiological implications of impaired channel function. For instance, in gastric mucosa, K + channel function is a prerequisite for acid secretion of parietal cells. In epithelial cells of small intestine, K + channels provide the driving force for electrogenic transport processes across the plasma membrane, and they are involved in cell volume regulation. Fine tuning of salt and water transport and of K + homeostasis occurs in colonic epithelia cells, where K + channels are involved in secretory and reabsorptive processes. Furthermore, there is growing evidence for changes in epithelial K + channel expression during cell proliferation, differentiation, apoptosis, and, under pathological conditions, carcinogenesis. In the future, integrative approaches using functional and postgenomic/proteomic techniques will help us to gain comprehensive insights into the role of K + channels of the gastrointestinal tract. 1 Origin of the channel names: "Shaker": Drosophila melanogaster c arrying a mutated "shaker" channel gene exhibited shaking behavior when recovering from diethylether anesthesia (471); "Shab": Sha ker cognate B ; "Shaw" Sha ker cognate W ; "Shal" Sha ker cognate L (61); "EAG" ( e ther à go-go g ene): flies carrying a mutated "eag" channel gene exhibited movements during recovery from diethylether anesthesia which were reminiscent of dancers at the "Whisky-à-Go-Go" night club (West Hollywood) (276, 673); "ERG": " e ther à go-go r elated g ene" (658); "ELK": " e ther à go-go l ike g ene" (658); "Slo" (slowpoke): a slow, noninactivating Ca 2+ -dependent K + current orignally descirbed in flies (16, 129).