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Potassium Channel Activity Recorded from the Apical Membrane of Freshly Isolated Epithelial Cells in Rat Caudal Epididymis¹

^a Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, N.T. Hong Kong, China

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 (K_D =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.

¹ This work was supported by Hong Kong Research Grant Committee awarded to Y.H.

² Correspondence. FAX: 852 2603 5022; yu-huang{at}cuhk.edu.hk

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