The effect of the anthelmintic emodepside at the neuromuscular junction of the parasitic nematode Ascaris suum
Here we report on the action of the novel cyclo-depsipeptide anthelmintic, emodepside, on the body wall muscle of the parasitic nematode, Ascaris suum. Emodepside caused (i) muscle relaxation, (ii) inhibition of muscle contraction elicited by either acetylcholine (ACh), or the neuropeptide, AF2 (KHEYLRFamide) and (iii) a rapid relaxation of muscle tonically contracted by ACh. The inhibitory action of emodepside on the response to ACh was not observed in a denervated muscle strip, indicating that it may exert this action through the nerve cord, and not directly on the muscle. Electrophysiological recordings showed emodepside elicited a Ca++-dependent hyperpolarization of muscle cells. Furthermore, the response to emodepside was dependent on extracellular K+, similar to the action of the inhibitory neuropeptides PF1 and PF2 (SDPNFLRFamide and SADPNFLRFamide). Thus emodepside may act at the neuromuscular junction to stimulate release of an inhibitory neurotransmitter or neuromodulator, with a similar action to the PF1/PF2 neuropeptides.(Received June 21 2002)
(Revised August 22 2002)
(Revised September 17 2002)
(Accepted September 17 2002)
Key Words: anthelmintic; Ascaris suum; neuropeptide.
c1 Corresponding author: Neuroscience Research Group, University of Southampton, Bassett Crescent East, Southampton SO16 7PX. Tel: +44 (0) 2380 594295. Fax: +44 (0) 2380594319. E-mail: R.J.Walker@soton.ac.uk