Cho, S.Spencer, E.Baker, S.Han, I.Park, K.Monaghan, K.Ward, S.Sanders, K.Koh, S.2008-08-122008-08-122005Journal of Physiology, 2005; 565(1):243-2590022-37511469-7793http://hdl.handle.net/2440/47318Published online before print March 17, 2005. The definitive version is available at www.blackwell-synergy.comThe excitability of smooth muscles is regulated, in part, by background K+ conductances that determine resting membrane potential. However, the K+ conductances so far described in gastrointestinal (GI) muscles are not sufficient to explain the negative resting potentials of these cells. Here we describe expression of two-pore K+ channels of the TASK family in murine small and large intestinal muscles. TASK-2, cloned from murine intestinal muscles, resulted in a pH-sensitive, time-dependent, non-inactivating K+ conductance with slow activation kinetics. A similar conductance was found in native intestinal myocytes using whole-cell patch-clamp conditions. The pH-sensitive current was blocked by local anaesthetics. Lidocaine, bupivacaine and acidic pH depolarized circular muscle cells in intact muscles and decreased amplitude and frequency of slow waves. The effects of lidocaine were not blocked by tetraethylammonium chloride, 4-aminopyridine, glibenclamide, apamin or MK-499. However, depolarization by acidic pH was abolished by pre-treatment with lidocaine, suggesting that lidocaine-sensitive K+ channels were responsible for pH-sensitive changes in membrane potential. The kinetics of activation, sensitivity to pH, and pharmacology of the conductance in intestinal myocytes and the expression of TASK-1 and TASK-2 in these cells suggest that the pH-sensitive background conductance is encoded by TASK genes. This conductance appears to contribute significantly to resting potential and may regulate excitability of GI muscles.enCopyright © 2005 The Physiological Society.Gastrointestinal TractIntestinesOocytesCells, CulturedMuscle CellsAnimalsMice, Inbred BALB CXenopus laevisMicePotassiumPotassium Channels, Tandem Pore DomainNerve Tissue ProteinsIon Channel GatingMembrane PotentialsElectric ConductivityHydrogen-Ion ConcentrationJournal article00200821302008081214411510.1113/jphysiol.2005.0845740002293446000232-s2.0-1944436238542340