Neuromuscular physiology of Grillotia erinaceus metacestodes (Cestoda: Trypanorhyncha) in vitro

Abstract

SUMMARYIsometric tension recordings and the single sucrose-gap technique were used to record mechanical and electrical activity from Grillotia erinaceus metacestodes in vitro. Both complete preparations and those cut longitudinally (to allow access of the bathing medium to the region of the somatic muscle) showed spontaneous contractions of frequency ≃ 1/min in Hanks’ Balanced Salt Solution (HBSS) at 13 °C. Changing the pH, temperature or osmolarity of the HBSS did not improve the activity but rather abolished it at extremes of these variables, so confirming the adequacy of the experimental environment for further work. The neurotoxin tetrodotoxin (TTX; 3 × 10−6 M) failed to abolish or modify these spontaneous contractions although excitatory and inhibitory responses to 5-hydroxytryptamine (5-HT) and acetylcholine (ACh) respectively were demonstrated. Electrical recordings showed that spontaneous contractions were mediated by slow membrane depolarizations upon which spike-like potentials were often superimposed. 5-HT was shown to mediate its excitatory effect via membrane depolarization and an increase in the frequency of both slow depolarization and spikes. In contrast, inhibition by ACh was accompanied by membrane hyperpolarization and loss of all regenerative electrical activity. Electric field stimulation of the preparation using a range of stimulus parameters failed to demonstrate a functional motor innervation to the somatic muscle.