Levamisole-activated single-channel currents from muscle of the nematode parasite Ascaris suum.
1. The patch-clamp technique was used to examine levamisole-activated channels in muscle vesicles from Ascaris suum. Cell-attached and isolated inside-out patches were used. 2. Levamisole (1-90 microM), applied to the extracellular surface, activated channels which had apparent mean open-times in the range 0.80-2.85 ms and linear I/V relationships with conductances in the range 19-46 pS. Ion-replacement experiments showed the channels to be cation selective. 3. The kinetics of the channels were analysed. Generally open- and closed-time distributions were best fitted by two, and three exponentials respectively, indicating the presence of at least two open states and at least three closed states. The distributions of burst-times were best-fitted by two exponentials. 4. Channel open- and burst-times were voltage-sensitive: at low levamisole concentrations (1-10 microM), they increased with hyperpolarization. At higher concentrations of levamisole (30 microM and 90 microM) flickering channel-block was observed at hyperpolarized potentials. Using a simple channel-block model, values for the blocking dissociation constant, KB were determined as 123 microM at -50 mV, 46 microM at -75 mV and 9.4 microM at -100 mV. 5. At the higher concentration of levamisole (30 microM and 90 microM) long closed-times separating 'clusters' of bursts were observed, at both hyperpolarized and depolarized membrane potentials and this was interpreted as desensitization.
Robertson
S J
SJ
Dept of Preclinical Veterinary Sciences, Royal (Dick) School of Veterinary Studies, University of Edinburgh.
Martin
R J
RJ
D000818:Animals; D017165:Ascaris suum / Q000187:drug effects* / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D007700:Kinetics; D007978:Levamisole / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000378:metabolism
D007473:Ion Channels; D007978:Levamisole