Fig. 1. (A) Acetylcholine (nicotinic) receptor -subunit of Ascaris suum (ASAR-1 GenBank Accession No. AJ011382) and protein kinase phosphorylation sites. The -subunit combines with other subunits to form the pentameric receptor ion-channel membrane protein. The regions TM1, TM2, TM3 and TM4 are transmembrane regions. The region between TM3 and TM4 is exposed to the cytoplasm and contains consensus serine (S), threonine (T) and tyrosine (Y) phosphorylation sites. The structural motifs S, T or Y are consensus sites recognized by kinases: C, protein kinase C; A, protein kinase A; G, protein kinase G; T, tyrosine kinase; and CaM, Ca²⁺/calmodulin kinase. (B) Representative responses to levamisole (Lev) and acetylcholine (ACh). The amplitude of the first peak was measured for experimental purposes. The secondary component or slow-phase responses to levamisole and acetylcholine (arrows) were not always present but were seen in approximately one-third of the responses; they were more labile than the first component and may have arisen as a secondary effect of calcium entry following stimulation of the nicotinic receptors, or following stimulation of a metabotrophic (muscarinic) receptor (Hwang et al., 1999).

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