J. exp. Biol. (1980), 88, 147-159 147 With S figures Wrinted in Great Britain THE PHARMACOLOGICAL PROFILE OF THE ACETYLCHOLINE RESPONSE OF A CRUSTACEAN MUSCLE BY EVE MARDER Biology Department, Brandeis University Waltham, MA 02254, USA AND DANIELE PAUPARDIN-TRITSCH Laboratoire de Neurobiologie, Ecole Normale Supirieure, 46 rue d'Ulm, Paris, 75005, France (Received 19 December 1979) SUMMARY A pharmacological analysis was made of the depolarizing acetylcholine (ACh) response found on the gastric mill 1 muscles of the crabs Cancer pagurus, Cancer irroratus and Cancer borealis. Acetylcholine, carbamylcholine, trimethylammonium, nicotine, and dimethyl-4-phenyl-piperazinium were effective in producing contractures and depolarizations in these muscles. No response to decamethonium, suberyldicholine, acetyl-/?-methylcholine, carbamyl-^-methylcholine, pilo- carpine and oxotremorine could be detected. High concentrations of muscarinic agonists (io~ 4 to io~ 3 M) potentiated and prolonged the ACh iontophoretic response. When the acetylcholinest- erase activity was inhibited with neostigmine, or when the response was elicited with carbamylcholine, muscarinic agonists partially inhibited the response. ACh responses were most effectively blocked by vertebrate nicotinic ganglionic antagonists, including dihydro-/?-erythroidine, pempidine, and mecamylamine. a-Bungarotoxin was without effect on the ACh response. INTRODUCTION Acetylcholine (ACh) is the neurotransmitter at vertebrate skeletal neuromuscular junctions and mimics the effects of the natural transmitter at neuromuscular junctions in many invertebrates (Gerschenfeld, 1973). These include animals as diverse as nematodes (Baldwin & Moyle, 1949; Del Castillo, DeMello & Morales, 1963), leech (Kuffler, 1978; Flacke & Yeoh, 1968), the polychaete worm Syllis spongiphila (Anderson & Mrose, 1978), and various molluscs (Twarog, i960; Liebeswar et al. 1975; Taraskevich et al. 1977; Elliott, 1979). Until recently there were no known cases of arthropod muscles with postsynaptic ACh receptors and cholinergic neuromuscular junctions. Futamachi (1972) first suggested the presence of ACh receptors on an arthropod muscle. This was followed by the discovery that some of the muscles of the stomatogastric system in decapod ^lstacea receive cholinergic excitatory neuromuscular innervation (Marder, 1974a, b, 1976).