Levamisole‐activated single‐channel currents from muscle of the nematode parasite Ascaris suum

Abstract

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. At the higher concentration of levamisole (30 JM and 90 gAM) long closed-times separating 'clusters' of bursts were observed, at both hyperpolarized and depolarized membrane potentials and this was interpreted as desensitization.

Activation and cooperative multi‐ion block of single nicotinic‐acetylcholine channel currents of Ascaris muscle by the tetrahydropyrimidine anthelmintic, morantel

“…The technique of Colquhoun and Sakmann (1985, p.505) Morantol block of nicotinic channels Results When added to the pipette solution, morantel activated single non-selective cation channel currents in membrane patches of vesicles isolated from the somatic muscle cells of Ascaris suum; no such events were observed in the absence of an agonist of the nAChRs (n -84). The conductance and kinetics of activation of these currents are similar to those described for acetylcholine-and levamisole-activated single-channel currents ; Robertson & Martin, 1993a). The concentration-dependence of activation of these nicotinicacetyleholine receptor currents (nAChR) has been studied In relation to other agonists (Robertson & Martin, 1993a) Both main-and sub-conductance states exhibit inward rectification Figure 2a shows examples of single-channel openings to the main conductance state, as recorded from an excised inside-out patch in the presence of 6 gM morantel and a range of holding potentials (+ 75 mV to -75 mV).…”

“…The conductance and kinetics of activation of these currents are similar to those described for acetylcholine-and levamisole-activated single-channel currents ; Robertson & Martin, 1993a). The concentration-dependence of activation of these nicotinicacetyleholine receptor currents (nAChR) has been studied In relation to other agonists (Robertson & Martin, 1993a) Both main-and sub-conductance states exhibit inward rectification Figure 2a shows examples of single-channel openings to the main conductance state, as recorded from an excised inside-out patch in the presence of 6 gM morantel and a range of holding potentials (+ 75 mV to -75 mV). The individual current amplitudes were clearly greater at negative holding potentials, the unitary conductance increasing from (mean + s.e.mean; n=6 patches) 32.41 + 1.09 pS at + 75 mV to 40.4+ 1.1 pS at -75 mV.…”

“…Thus for the purposes of burst analysis a critical time (tcnt) was determined numerically (Robertson & Martin 1993a) for each data set. All closed-times with a duration less than tent were defined as those being within a burst of openings, while all closures with a duration greater than tcit were defined as those with separate bursts.…”

“…In a recent study Robertson and Martin (1993a) found that the anthelmintic levamisole both activated and blocked single nicotinic AChR currents isolated from the somatic muscle cells of Ascaris, even though this compound exhibits no clear selfantagonism with respect to the macroscopic nicotinic AChR currents (Harrow & Gration, 1985). This may be explained by the fact that levamisole produced fast-flickering open channelblock, which was marked only at holding potentials more negative than the normal resting potential of the cell.…”

Eight genes are required for functional reconstitution of the Caenorhabditis elegans levamisole-sensitive acetylcholine receptor

“…3B). This inhibition likely resulted from openchannel block by the positively charged levamisole molecule (10,25,26). To test this hypothesis, we performed voltage ramps and demonstrated that 500 M levamisole produced a slight voltagedependent block of L-AChR responses (Fig.…”