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

• Published in: Parasitology 2004-12, Vol.129 (6), p.779-793
• Main Authors: KUMAR, D., WHITE, C., FAIRWEATHER, I., McGEOWN, J. G.
• Format: Article
• Language: English
• Subjects: Actin; Actins - physiology; Animals; Biochemistry; Biological and medical sciences; Blocking; Boltzmann transport equation; Calcium - physiology; Calcium buffering; calcium channel blockers; Calcium channels (voltage-gated); Calcium conductance; Calcium ions; Deactivation; Depolarization; Electric potential; electrophysiology; Fasciola hepatica; Fasciola hepatica - cytology; Fasciola hepatica - physiology; fluorescent labeling; Fundamental and applied biological sciences. Psychology; General aspects; General aspects and techniques. Study of several systematic groups. Models; immunocytochemistry; inhibitors; Invertebrates; ion channels; Kinetics; liver flukes; membrane potential; Membrane Potentials - drug effects; Membrane Potentials - physiology; Microscopy, Electron, Scanning; Microscopy, Fluorescence; muscle; Muscle contraction; muscle fibers; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - physiology; Muscles; Myosin; Myosins - physiology; Nimodipine; Parasites; Pharmacology; Physiology; Potash; Potassium; Potassium - physiology; potassium channel blockers; Potassium Channel Blockers - pharmacology; potassium channels; Potassium channels (calcium-gated); Potassium channels (voltage-gated); Potassium Channels - physiology; Potassium conductance; Proteomics; Quaternary Ammonium Compounds - pharmacology; Rectifiers; Resistance; Scanning electron microscopy; Smooth muscle; sucker muscle; Tetraethylammonium; Titanium alloys; Verapamil; voltage-clamp
• ISSN: 0031-1820; 1469-8161
• DOI: 10.1017/S0031182004006110

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 EK 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 μM) 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 μM) and by 59±4% by nimodipine (30 μM). Superfusion with BAPTA-AM (50 μM), 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.