title: Potassium channel activity recorded from the apical membrane of freshly isolated epithelial cells in rat caudal epididymis.
abstract: K+ channels were recorded in excised, inside-out patches from the apical membrane of the freshly isolated tubule of the caudal portion of the rat epididymis. With asymmetric K+ concentrations in bath and pipette (140 mM K+in/6 mM K+out), the channels had a slope conductance of 54.2 pS at 0 mV. The relative permeability of K+ over Na+ was about 171 to 1. The channels were activated by intracellular Ca2+ and by membrane depolarization. These channels belong to a class defined as "intermediate-conductance Ca2+-activated K+ channel. " External tetraethylammonium ions (TEA+) caused a flickery block of the channel with reduction in single-channel current amplitude measured at a range of holding membrane potentials (-40 to 60 mV). Activity of the K+ channels was inhibited by intracellular ATP (KD =1.188 mM). The channel activity was detected only occasionally in patches from the apical membrane (about 1 in 17 patches containing active channels). The presence of the intermediate-conductance Ca2+-activated K+ channels indicates that they could provide a route for K+ secretion in a Ca2+-dependent process responsible for a high luminal K+ concentration found in the epididymal duct of the rat.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology*; D003981:Diazoxide / Q000494:pharmacology; D004553:Electric Conductivity; D004822:Epididymis / Q000648:ultrastructure*; D004847:Epithelial Cells / Q000648:ultrastructure*; D008297:Male; D008564:Membrane Potentials; D011188:Potassium / Q000008:administration & dosage / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019789:Tetraethylammonium / Q000494:pharmacology