The nematode neuropeptide, AF2 (KHEYLRF-NH2), increases voltage-activated calcium currents in Ascaris suum muscle.

BACKGROUND AND PURPOSE

Resistance to all the classes of anti-nematodal drugs like the benzimidazoles, cholinergic agonists and avermectins, has now been recorded in parasites of animals and/or humans. The development of novel anthelmintics is an urgent and imperative need. Receptors of nematode neuropeptides have been suggested to be suitable target sites for novel anthelmintic drugs.

EXPERIMENTAL APPROACH

To investigate the effect of AF2 on calcium-currents in Ascaris suum somatic muscle cells we employed the two-micropipette current-clamp and voltage-clamp techniques and a brief application of AF2.

KEY RESULTS

Here we report the isolation of voltage-activated, transient, inward calcium currents. These currents are similar in characteristics to Caenorhabditis elegans UNC-2 type currents, non-L-type calcium currents. Following a 2-minute application of 1 microM AF2 , there was a significant long-lasting increase in the transient inward calcium current; AF2 increased the maximum current (from -84 nA to -158 nA) by shifting the threshold in the hyperpolarising direction (V (50) changed from -7.2 to -12.8 mV) and increasing the maximum conductance change from 1.91 to 2.94 microS.

CONCLUSION AND IMPLICATIONS

These studies demonstrate a mechanism by which AF2 increased the excitability of the neuromuscular system by modulating calcium currents in nematodes. A selective small molecule agonist of the AF2 receptor is predicted to increase the contraction and act synergistically with cholinergic anthelmintics and could counter resistance to these compounds.