Functional ryanodine receptor channels in flatworm muscle fibres

Abstract

Caffeine, which stimulates intracellular Ca2+ release channels known as ryanodine receptor (RyR) channels, induces contraction of individual muscle fibres dissociated from the trematode Schistosoma mansoni, and the turbellarians Dugesia tigrina and Procerodes littoralis. Caffeine is much more potent on S. mansoni fibres (EC50 0.7 mM) than those from D. tigrina or P. littoralis (3.2 mM and 4.6 mM, respectively). These caffeine-induced contractions are blocked by ryanodine, confirming the presence of functional RyR channels in these flatworm muscles. However, the contractions are not blocked by typical RyR channel blockers ruthenium red or neomycin, indicating that there may be important pharmacological differences between the RyR channels in this early-diverging phylum and those of later animals. These studies demonstrate that RyR channels are present in the muscle of these flatworms, and that the sarcoplasmic reticulum stores sufficient Ca2+ to support contraction.

FMRFamide-Like Peptides (FLPs) Enhance Voltage-Gated Calcium Currents to Elicit Muscle Contraction in the Human Parasite Schistosoma mansoni

“…For example, under these same conditions in which extracellular Ca 2+ is taken away, caffeine can elicit contraction via a ryanodine-sensitive intracellular store [18]. Since YIRFamide does not elicit contractions under the same conditions, it demonstrates that the FLP contraction does not utilize this intracellular store, and reinforces the conclusion that the FLP-induced contractions depend on an influx of extracellular Ca 2+ (Figure 2).…”

Control of calcium homeostasis in Schistosoma mansoni

“…Furthermore, the addition of ryanodine induced the contraction of whole worms, in vitro. These data were corroborated by Day et al (2000) which have showed that caffeine, an agonist of RyR, was able to contract isolated muscle fibres. In this way we may propose that the presence of sarcoplasmic reticulum calcium stores, with both SERCA and RyR, is essencial to support worm contraction.…”

Identification of Intracellular and Plasma Membrane Calcium Channel Homologues in Pathogenic Parasites

“…Experimental observations also suggest the possibility for drug selectivity. For example, S. mansoni muscle fibres show RyR-like Ca 2+ responses that are activated by caffeine but insensitive to the classical RyR blockers, ruthenium red and neomycin [118]. Drugs with selectivity for insect RyRs have been described and these have been utilized to develop novel insecticides, which do not affect mammalian RyRs [119].…”