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In the present work, we study the effect of different stimuli (living preys, its homogenate, and reduced glutathione (GSH)) on the discharge of desmonemes in the freshwater cnidarian, Hydra plagiodesmica (Dioni, 1968) (Cnidaria: Hydrozoa). Once confirmed their stimulatory effect, we choose GSH to analyze the relevance of Ca2+, the probable identity of the sensory receptor molecule, and the specific signalling pathway driving the discharge mechanism. Our results show that not only mechanical, but also chemical stimuli by itself may stimulate the discharge of desmonemes. Using calcium chelators, we verify that the discharge mechanism triggered by GSH is dependent on calcium. By mean of drugs that inhibit proteins pertaining to canonical signalling pathways, including GPCRs, we show that GSH causes the influx of Ca2+ via L-type voltage sensitive calcium channel (VGCC), and its release by mean of endoplasmic reticulum calcium channels. Moreover, our results suggest that the putative receptor for GSH is a GPCR coupled to Gq, which produces IP3 and Ca2+ as second messengers. Finally, we show that the genome of Hydra vulgaris (Pallas, 1766) predicts the existence of the different subunits of L-type VGCC, showing a high level of conservation when compared with other groups of Metazoa. [ABSTRACT FROM AUTHOR]

Our laboratory has previously examined the effect of neuropeptides on the activity of the hypostome of the hydra Hydra plagiodesmica Dioni, 1968 (Cnidaria: Hydrozoa). These results showed that the hypostome, a structure extruded during feeding, responds to myoregulatory peptides and that this mechanism might be regulated by changes in the cytosolic levels of calcium (Ca2+). We analyse now the ways in which Ca2+ modulates hypostome activity during feeding. The use of calcium chelators confirms that Ca2+ is relevant in inducing hypostome extrusion. The assay of compounds that modulate the activity of Ca2+ channels in the endoplasmic reticulum suggests that, beyond the extracellular influx of calcium, intracellular sources of the ion are involved and might include both ryanodine receptors (RyR) and the inositol 1,4,5-trisphosphate receptor (IP3R). Bioinformatic searches based on sequences of RyR and IP3R of humans (Homo sapiens Linnaeus, 1758) show that IP3Rs are present in all groups analysed, including Fungi and Choanoflagellata. Although H. plagiodesmica responds to caffeine and ryanodine, which are known to modulate RyRs, this family of receptors seems not to be predicted in Cnidaria, suggesting that this phylum either lacks these kinds of channels or that they possess a different structure compared with those possessed by other Metazoa. [ABSTRACT FROM AUTHOR]

Allatotropin is a pleiotropic peptide originally characterized in insects. The existence of AT neuropeptide signaling was proposed in other invertebrates. In fact, we previously proposed the presence of an AT-like system regulating feeding behavior in Hydra sp. Even in insects, the information about the AT signaling pathway is incomplete. The aim of this study is to analyze the signaling cascade activated by AT in Hydra plagiodesmica using a pharmacological approach. The results show the involvement of Ca 2+ and IP 3 signaling in the transduction pathway of the peptide. Furthermore, we confirm the existence of a GPCR system involved in this pathway, that would be coupled to a G q subfamily of Gα protein, which activates a PLC, inducing an increase in IP 3 and cytosolic Ca 2+ . To the best of our knowledge, this work represents the first in vivo approach to study the overall signaling pathway and intracellular events involved in the myoregulatory effect of AT in Hydra sp., (Copyright © 2020 Elsevier Inc. All rights reserved.)