An investigation into the mechanism of action of the novel anthelmintic emodepside

Willson, James Michael (2003) An investigation into the mechanism of action of the novel anthelmintic emodepside. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The action of emodepside on the body wall muscle of the nematode A. suum was investigated. Emodepside (10μM) was applied for 10mins prior to ACh addition and caused a reduction in the ACh induced contraction of 39 ± 4%. Emodepside was also shown to relax the dorsal muscle strip (DMS) following prolonged contraction with ACh. A slow relaxation of the DMS was then observed over a period of 10mins. Addition of 10μM emodepside at the point of maximum contraction, caused a faster relaxation of the DMS, 9.0%min^-1 ± 0.3 compared to the ACh control. The action of emodepside was similar to that of an inhibitory neuropeptide PF2 (SADPNFLRFamide). PF2 (1μM) caused a faster relaxation of the DMS (9.2%min^-1 ± 0.4) compared to ACh control (7.4% min^-1 ± 0.3), similar to emodepside. The ionic dependence of the response of A. suum muscle to emodepside was investigated using an intracellular electrophysiology recording technique. A 2 min perfusion of emodepside over muscle cells caused a slow hyperpolarisation of 5.5 ± 0.1 mV, with no consistent change in input conductance after 30 min. A calcium and potassium component of emodepside action was demonstrated. In the absence of calcium, emodepside (10μM) caused no change in membrane potential. Re-introduction of calcium ions, resulted in a slow hyperpolarisation of 5.5 ± 1.1 mV. The potassium channel blockers 4-aminopyridine and tetra-ethylammonium also blocked the emodepside induced hyperpolarisation of A. suum muscle cells. To elucidate whether emodepside acts pre-or post-synaptically at the neuromuscular junction, the effect of emodepside was investigated on a denervated muscle strip preparation. Application of emodepside (10μM) to the denervated muscle strip caused no reduction in A Ch induced contraction. These studies on A. suum therefore suggest emodepside may inhibit nematode motility by acting pre-synaptically to trigger the release of an inhibitory neuropeptide.