The very small-conductance K+ channel KVLQT1 and epithelial function

K(V)LQT1 (KCNQ1) is a very small conductance K+ channel distributed widely in epithelial and non-epithelial tissues. Its specific biophysical and pharmacological properties are determined by the regulatory subunits I-sK (KCNE1) and MiRP2 (KCNE3). In epithelial cells of the inner ear, pancreas, and airways it interacts with I-sK to conduct a voltage-gated and slowly activating K+ current. In the colon it coassembles with KCNE3 to conduct an instantaneous and constitutively active K+ current. In Cl- secretory epithelia, such as the colon and pancreas, this K+ channel provides the driving force for Cl- exit and is located in the basolateral membrane. In the inner ear it enables luminal secretion of K+ into the endolymphatic space. The functional relevance of K(V)LQT1 to epithelial function is revealed by blocking it pharmacologically or by studying animals with a genetic defect for it, which result in the breakdown of colonic Cl- secretion and endolymph production, respectively. K(V)LQT1 K+ channels are activated via cAMP or Ca2+ and inhibited by the chromanol 293B. Interaction with as yet unknown regulatory subunits may determine the properties of K(V)LQT1 in the rectal gland and other epithelial tissues in which K(V)LQT1 is not inhibited by chromanols.