Electrophysiological and pharmacological characteristics of buccal smooth muscle of the pest slug Deroceras reticulatum

Buccal mass muscle of the pest slug Deroceras reticulatum was examined by c onventional tension recording and the sucrose-gap electrophysiological tech nique. Elevated potassium salines induced dose-dependent depolarisations ac companied by tonic contractures with superimposed rapid twitch contractions , The latter were suppressed at over 40 mmol . l(-1) external potassium, wh ere depolarisation-induced inactivation of voltage-sensitive calcium channe ls may have occurred. Acetylcholine caused significant dose-dependent depol arisations and tonic contractures, while 5-hydroxy tryptamine induced lower depolarisations accompanied by phasic contractile activity superimposed on low level tonic force. Of the purines examined only guanosine triphosphate caused significant mechanical activity above a threshold of 0.1 mu mol . l (-1). The tetrapeptides inhibited buccal muscle spontaneous activity, but t he related small cardioactive peptide B was weakly excitatory. The amino ac ids glutamate and gamma-aminobutyric acid were weakly excitatory on buccal muscle while the molluscicides metaldehyde and methiocarb disrupted normal mechanical activity of the feeding musculature. Acetylcholine and 5-hydroxy tryptamine appear to have major roles in regulating feeding muscle activity , seemingly modulated by guanosine triphosphate and inhibited by phenylalan ine-methionine-argininephenylalanine-NH2 and phenylalanine-leucine-arginine -phenylalanine-NH2.