Ion channels ofFasciola hepaticaincorporated into planar lipid bilayers

Abstract

Ion channels are important target sites of anthelmintics, but little is known about those in Fasciola hepatica. In this work, we applied a planar lipid bilayer technique to characterize the properties of single ion channels in F. hepatica. Under a 200/40 mM KCl gradient, a large conductance channel of 251 pS was observed in 18% of the membranes studied. The channel was selective to K(+) over Cl(-) with a permeability ratio of K(+) to Cl(-) (PK/PCl) of 4.9. Open state probability (Po) of the channel was less than 0.5 and dependent on voltage (-60 to approximately +40 mV) and Ca(2+) (approximately 100 microM). The other two types of single channels observed in 11 and 5% of membranes, respectively, were a K(+)-permeable channel of 80 pS (PK/PCl=4.6) and a Cl(-)-permeable channel of 64 pS (PK/PCl=0.058). Open state probability of both channels showed little voltage dependence. The results indicate that distinct single channels of 60 to approximately 251 pS are present in relative abundance and, in addition, that the planar lipid bilayer technique can be a useful tool for the study of single ion channels in F. hepatica.

Electrophysiological characterization of potassium conductive pathways in Trypanosoma cruzi

“…The relative permeability ratio P K /P Cl calculated was about 5, similar to the reported values for potassium channels in Fasciola hepatica [Jang et al, 2004] and Dictyostelium discoideum [Yoshida et al, 1997]. Further work is necessary to obtain a complete biophysical characterization of this channel as well as its possible cellular functions and molecular identity.…”

Molecular and Electrophysiological Characterization of a Novel Cation Channel of Trypanosoma cruzi

“…Characterization of K + channels, although detailed and exhaustive in some cases, is mainly limited to bacterial (KcsA) and mammalian channels, with some particular cases of model organisms like Drosophila and C. elegans . In Fasciola hepatica [60]and Dictyosteliumdiscoideum [61] the presence of K + channels with relative permeability ratio P K /P Cl of 5 and 7, respectively, have been previously reported, suggesting that the selectivity of some channels in these organisms is not as high as for bacterial or mammalian K + channels.…”

Electrophysiological and pharmacological characterization of K+-currents in muscle fibres isolated from the ventral sucker ofFasciola hepatica

“…This is, to the best of our knowledge, the first such study on muscle from F. hepatica. It is only the second voltage-clamp study on cells of any type from this organism, a non-specific cation current having recently been described in neurons isolated from F. hepatica (Kim et al 2002), although ion channels from F. hepatica have also been studied in lipid bilayers (Jang et al 2003). We describe here outward K + -currents evoked during depolarization, along with their unusual pharmacological profile.…”

“…Another possibility is that an opposing inward current may have shifted the reversal potential positively with regard to E K , with either a chloride (Large & Wang, 1996) or a non-specific cation conductance (Loirand et al 1991) being possible candidates. A non-specific cation current has recently been identified in neurons isolated from F. hepatica (Kim et al 2002), while both K + -and Cl x -channels have been identified in lipid bilayer experiments using extracts from homogenized flukes (Jang et al 2003). Unfortunately, this technique does not allow the tissue of origin to be identified.…”

“…The use of the patch-clamp technique has led to a huge growth in our understanding of the ion channels responsible for excitation in mammalian nerve and muscle (for review, see Sakmann & Neher, 1984), but relatively few studies have addressed these issues from an electrophysiological perspective in flatworms (Keenan & Koopowitz, 1981Bricker, Pax & Bennett, 1982 ;Solon & Koopowitz, 1982 ;Bennett & Kohler, 1987 ;Blair et al 1991 ;Blair & Anderson, 1993Day et al 1993Day et al , 1995Kim et al 2002 ;Cobbett & Day, 2003 ;Jang et al 2003). In this paper we describe the isolation and identification of muscle fibres from the ventral sucker of the liver fluke, F. hepatica and summarize the results of voltage-clamp experiments carried out on these cells.…”