Physiology of obliquely striated muscle fibres within Grillotia erinaceus metacestodes (Cestoda: Trypanorhyncha)

The tentacular bulb of Grillotia erinaceus metacestodes consists of obliquely striated muscle fibres with obvious motor end-plates. In this study isometric tension recordings and intracellular microelectrodes have been used to record mechanical and electrical activity from single isolated bulbs. Bulbs were mechanically quiescent and displayed resting membrane polentials (RMP) in the region of −49 to −64 mV with a mean RMP of −56 mV (n = 60). The membrane potential varied with [K+]o in a manner consistent with the RMP being determined largely by the K+ equilibrium potential. High K+ solution (> 15 mM) caused membrane depolarization and contraction of the preparation with the contraction showing both phasic and tonic components. L-glutamate caused membrane depolarization, contraction of quiescent preparations and increased the amplitude of electrically evoked responses. In contrast, 5-HT, dopamine, histamine, adrenaline, GABA, noradrenaline and D-glutamate, at concentrations up to and including 10−3 M, were without apparent affect, although acetylcholine, at relatively high concentrations (≥ 10−4 M) slightly reduced the amplitude of field-evoked contractions.