Molecular basis of the differential sensitivity of nematode and mammalian muscle to the anthelminitic agent levamisole

D. RAYES; M.J. DE ROSA; M. BARTOS; C. BOUZAT

JOURNAL OF BIOLOGICAL CHEMISTRY

The American Society for Biochemistry and Molecular Biology

Año: 2004 vol. 279 p. 36372 - 36381

0021-9258

Levamisole is an anthelmintic agent that exerts its therapeutic effect by acting as a full agonist of the nicotinic receptor (AChR) of nematode muscle. Its action at the mammalian muscle AChR has not been elucidated to date despite its wide use as an anthelmintic in humans and cattle. By single-channel and macroscopic-current recordings we investigated the interaction of levamisole with the mammalian muscle AChR. Levamisole activates mammalian AChRs. However, single-channel openings are briefer than those activated by ACh and do not appear in clusters at high concentrations. The peak current induced by levamisole is about  3 % of that activated by ACh. Thus, the anthelmintic acts as a weak agonist of the mammalian AChR. Levamisole also produces open-channel blockade of the AChR. The apparent affinity for block (190 mM at -70 mV) is similar to that of nematode AChR, suggesting that differences in channel activation kinetics govern the different sensitivity of nematode and mammalian muscle to anthelmintics. To identify the structural basis of this different sensitivity, we performed mutagenesis targeting residues in the a subunit that differ between vertebrates and nematodes. The replacement of the conserved aG153 with the homologous glutamic acid of nematode AChR significantly increases the efficacy of levamisole to activate channels. Channel activity takes place in clusters having two different kinetic modes. The kinetics of the high open probability mode are almost identical when the agonist is ACh or levamisole. It is concluded that aG153 is involved in the low efficacy of levamisole to activate mammalian muscle AChRs.