Effects of the muscarinic agonist, 5-methylfurmethiodide, on contraction and electrophysiology of Ascaris suum muscle

Abstract

Contraction and electrophysiological effects of 5-methylfurmethiodide (MFI), a selective muscarinic agonist in mammals, were tested on Ascaris suum muscle strips. In a contraction assay, MFI produced weak contraction and was less potent than levamisole and acetylcholine. Atropine (3 µM) a nonselective muscarinic antagonist in mammalian preparations, did not affect contractions produced by MFI. Mecamylamine (3 µM) a nicotinic antagonist in A. suum preparations, blocked the MFI contractions indicating that MFI had weak nicotinic agonist actions. In two-micropipette currentclamp experiments MFI, at concentrations greater than 10 µM, produced concentration-dependent depolarizations and small increases in membrane conductance. The depolarizing effects were not abolished by perfusing the preparation in a calcium-free Ascaris Ringer solution to block synaptic transmission, suggesting that MFI effects were mediated by receptors on the muscle and were calcium-independent. A high concentration of mecamylamine, 30 µM, only reduced the depolarizing responses by 42%, indicating that MFI also had effects on non-nicotinic receptors. Three nonnicotinic effects in the presence of 30 µM mecamylamine were identified using voltage-clamp techniques: i) MFI produced opening of mecamylamine-resistant non-selective-cation channel currents; ii) MFI inhibited opening of voltage-activated potassium currents; and iii) MFI increased the threshold of voltage-activated calcium currents. We suggest that a drug that is more selective for voltage-activated potassium currents, without effects on other channels like MIF, may be exploited pharmacologically as a novel anthelmintic or as an agent to potentiate the action of levamisole. In a larval migration assay we demonstrated that 4-aminopyridine (4-AP: a potassium channel blocker) potentiated the effects of levamisole but MFI did not.

Anthelmintic resistance and homeostatic plasticity (Brugia malayi)

“…The rise in cytosolic calcium following opening of AChRs by levamisole then produces muscle contraction mediated by the calcium contraction coupling pathway 46 , 49 , 50 . TRP channels (TRP-2, GON-2 and CED-11) channels present in Brugia muscle also contribute to the muscle contraction 16 , 51 , 52 . TRP channels are subject to regulation by intracellular messengers including direct or indirect activation and inhibition by calcium and PKC 51 , 53 , 54 , Fig.…”

Whole-cell patch-clamp recording of nicotinic acetylcholine receptors in adult Brugia malayi muscle

“…In contraction assay and electrophysiological recordings from A. suum muscle, pyrantel > bephenium > levamisole > acetylcholine (Harrow and Gration, 1985; Martin et al ., 2004; Trailovic et al ., 2008). In reconstituted Haemonchus contortus L-AChRs, levamisole > acetelcholine > pyrantel in Hco-L-AChR1 subtype and in the Hco-L-AChR2 subtype, pyrantel > acetylcholine > levamisole (Boulin et al ., 2011).…”

Expression of five acetylcholine receptor subunit genes in Brugia malayi adult worms

“…Our expression data are consistent with results from whole-cell patch-clamp studies in B. malayi that found that AChRs are activated by cholinergic anthelmintics (levamisole, pyrantel, bephenium and tribendimidine) and that levamisole reversibly paralyzed adult worms ( Robertson et al., 2011 ). Biophysical and pharmacological features of body muscle ACh receptors in B. malayi ( Robertson et al., 2011 , 2013 ) suggest that the B. malayi AChRs are different from those in A. suum [( Martin et al., 2004; Trailovic et al., 2008 ) and H. contortus ( Boulin et al., 2011 ) and possibly more similar to those in C. elegans ( Boulin et al., 2008 ). The B. malayi AChRs in body muscle are less sensitive to both acetylcholine and levamisole than that in C. elegans , A. suum or O. dentatum ( Robertson et al., 2011 ).…”