Property of large conductance Ca2+-activated K+ channels from Fasciola hepatica incorporated into planar lipid bilayer

Fasciola hepatica causes biliary epithelial hyperplasia and obstructive jaundice in humans and animals. Using a planar lipid bilayer technique, we further characterized the single channel property of large conductance K+-permeable channels that were previously identified from F. hepatica. The single channel conductance was 254.7 ± 17.9 pS under a symmetrical 200/200 mM (cis/trans) KCl gradient. Open state probability (Po) varied from channel to channel at a given membrane potential and Ca2+ concentration, but increased with voltage (−60 to +40 mV) and cis Ca2+ (1-200 μM). Under a near bi-ionic condition of 200 mM [K+]cis/200 mM [Na+]trans, the permeability ratio of K+ to Na+ was 5.0. Charybdotoxin (1 μM) inhibited Po, whereas tetraethylammonium reduced the conductance (KD = 67.8 mM). Taken together, the results show that the single channel properties of the large conductance K+-permeable channels in F. hepatica are similar to those of large conductance Ca2+-activated K+ (BK) channels in general, but distinct from typical BK channels in the extent of voltage- and Ca2+-dependence, as well as permeability to Na+. This study further reveals a variant BK channel in F. hepatica that could serve as a new drug target to treat fascioliasis.