, Volume 169, Issue 8, pp 561-568

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

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Abstract

Buccal mass muscle of the pest slug Deroceras reticulatum was examined by conventional tension recording and the sucrose-gap electrophysiological technique. Elevated potassium salines induced dose-dependent depolarisations accompanied by tonic contractures with superimposed rapid twitch contractions. The latter were suppressed at over 40 mmol · l−1 external potassium, where depolarisation-induced inactivation of voltage-sensitive calcium channels may have occurred. Acetylcholine caused significant dose-dependent depolarisations 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 μmol · l−1. The tetrapeptides inhibited buccal muscle spontaneous activity, but the related small cardioactive peptide B was weakly excitatory. The amino acids 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-hydroxytryptamine appear to have major roles in regulating feeding muscle activity, seemingly modulated by guanosine triphosphate and inhibited by phenylalanine-methionine-arginine-phenylalanine-NH2 and phenylalanine-leucine-arginine-phenylalanine-NH2.

Accepted: 22 July 1999