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

Abstract

Fibres isolated from the ventral sucker of Fasciola hepatica were identified as muscle on the basis of their contractility, and their actin and myosin staining. They were voltage-clamped at a holding potential of -40 mV and depolarization-activated outward currents were characterized both electrophysiologically and pharmacologically. Activation was well fitted by a Boltzmann equation with a half-maximal potential of + 9 mV and a slope factor of -14.3 mV, and the kinetics of activation and deactivation were voltage-sensitive. Tail current analysis showed that the reversal potential was shifted by +46+/-3 mV when E(K) was increased by 52 mV, confirming that this was a K+-current with electrophysiological characteristics similar to delayed rectifier and Ca2+-activated K+-currents in other tissues. The peak current at + 60 mV was inhibited by 76+/-6% by tetrapentylammonium chloride (1 mM) and by 84+/-7% by Ba2+ (3 mM), but was completely resistant to block by tetraethylammonium (30 mM), 3,4-diaminopyridine (100 microM) and 4-aminopyridine (10 mM). Penitrem A, a blocker of high-conductance Ca2+-activated K+-channels reduced the current at +60 mV by 23+/-5%. When the effects of Ca2+-channel blocking agents were tested, the peak outward current at + 60 mV was reduced by 71+/-7% by verapamil (30 microM) and by 59+/-4% by nimodipine (30 microM). Superfusion with BAPTA-AM (50 microM), which is hydrolysed intracellularly to release the Ca2+-buffer BAPTA, also decreased the current by 44+/-16%. We conclude that voltage-and Ca2+-sensitive K+-channels are expressed in this tissue, but that their pharmacology differs considerably from equivalent channels in other phyla.

SLO-1-Channels of Parasitic Nematodes Reconstitute Locomotor Behaviour and Emodepside Sensitivity in Caenorhabditis elegans slo-1 Loss of Function Mutants

“…It has also been used as a BK channel inhibitor in a study on muscle fibres of the liver fluke Fasciola hepatica [62]. The concentration in those experiments was 10 µM, but the authors do not report, whether they tested other concentrations.…”

Neuropeptide signalling systems in flatworms

“…Firstly, the study of dispersed muscle fibres is expanding and more data should accumulate regarding the events associated with FLP-induced myoexcitation. For example, the protocol has been successfully applied to F. hepatica (Kumar et al 2003(Kumar et al , 2004. Secondly, more techniques are now becoming available to investigate the functional biology of flatworms, such as RNA interference (Boyle et al 2003 ;Skelly, Da'dara & Harn, 2003) and genetic transformation (Wippersteg et al 2002(Wippersteg et al , 2003(Wippersteg et al , 2005Gonzalez-Estevez et al 2003 ;Heyers et al 2003).…”

Comparison of biochemical and immunochemical properties of myosin II in taeniid parasites

“…They are conserved proteins, but differences in the variable regions, mainly in the filamentous segment, result in different biochemical and immunochemical characteristics (Werner and Rajan, 1992). Because of their antigenic differences, myosins have been distinguished in muscles of Fasciola hepatica (Kumar et al, 2003(Kumar et al, , 2004 and in T. solium (Ambrosio et al, 1997), and have been used in studies of protection against Schistosoma mansoni (Newport et al, 1987). Parasite myosin has been found in serum from patients with filariosis (Raghavan et al, 1992) and in the faeces of hamsters experimentally infected with adult T. solium (Ambrosio et al, 1997).…”