A voltage-dependent chloride channel from Tetrahymena ciliary membrane incorporated into planar lipid bilayers

Membrane vesicles from cilia of Tetrahymena thermophila were incorporated into a planar phospholipid bilayer membrane, and single-channel currents across the planar membrane were recorded under voltage-clamp conditions. A novel and reproducible chloride channel was observed when a mixture of phosphatidylethanolamine and phosphatidylcholine was used to form the planar lipid membrane but not when acidic phospholipid mixtures such as asolectin or a mixture containing phosphatidylserine. Using symmetrical 100 mM KCl solutions, the single-channel conductance of the fully open state (O1) was 73.1 pS, with sub-level (O2) conductance of 9.0 pS. The permeability ratio Pc1/Pk was calculated as 3.7, according to the Goldman-Hodgkin-Katz current equation. This channel exhibited characteristic voltage-dependent burst activities. With an increase in membrane potential, the lifetimes of both the burst and interburst states decreased. In the burst state, the frequency of transition between the O1 and O2 states was also voltage-dependent, mainly due to the decrease in the lifetime of the O1 state, with an increase in membrane potential. In addition, channel activity was inhibited by indanyloxyacetic acid-94 (IAA-94), an inhibitor of epithelial chloride channels.