Signaling mechanisms of vasopressin/oxytocin-type neuropeptide-induced muscle contraction in the sea cucumber Apostichopus japonicus.
This study reveals that holotocin induces muscle contraction in sea cucumbers through a Gαq-dependent signaling pathway, but further research is needed to confirm these findings in living organisms.
Where it sits
this study against the rest of the vasopressin corpusSummary and findings
This study investigated the signaling pathways of vasopressin/oxytocin-type neuropeptides in inducing muscle contraction in the sea cucumber Apostichopus japonicus. The research focused on the contraction of the longitudinal muscle of the body wall (LMBW) and identified the involvement of a Gαq-dependent pathway. The findings contribute to understanding the evolutionary conservation of muscle contraction mechanisms across species.
Abstract
The myoregulatory action of vasopressin/oxytocin (VP/OT)-type neuropeptides is evolutionarily conserved across Bilateria. In vertebrates, the signaling cascades involved have been comprehensively characterized in several muscle types, including uterine and gastrointestinal smooth muscles. VP/OT-type neuropeptide-induced muscle contraction or relaxation has been reported in a variety of invertebrates, but the downstream signaling pathways responsible for these effects have yet to be elucidated. Here, using heterologous cell systems and in vitro pharmacological experiments, we investigated the signaling pathways underlying VP/OT-type neuropeptide (holotocin) induced contraction of the longitudinal muscle of the body wall (LMBW) in the sea cucumber Apostichopus japonicus (phylum Echinodermata), a deuterostome invertebrate. Holotocin-induced contraction of the LMBW comprised two distinct phases: an initial rapid phasic contraction followed by a sustained tonic contraction. Pharmacological experiments revealed that upon binding to its receptor AjHOR, holotocin activates a Gαq-dependent pathway, leading to phospholipase C (PLC) activation and subsequent hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP<sub>2</sub>) into inositol 1,4,5-trisphosphate (IP<sub>3</sub>) and diacylglycerol (DAG). IP<sub>3</sub> triggers Ca<sup>2+</sup> release from intracellular Ca<sup>2+</sup> stores via IP₃ receptors (IP<sub>3</sub>R), but depletion of intracellular Ca<sup>2+</sup> does not activate store-operated Ca<sup>2+</sup> entry (SOCE). DAG activates protein kinase C (PKC), which may modulate the activity of ion channels in the plasma membrane, resulting in membrane depolarization, opening of voltage-gated Ca<sup>2+</sup> channels (VGCCs), and subsequent influx of extracellular Ca<sup>2+</sup>. Overall, this study reveals similarities and differences in the signaling pathways mediating smooth muscle contraction in invertebrates and vertebrates, providing new insights into the evolution of these mechanisms across the Bilateria.
Background
This paper addresses the mechanisms of muscle contraction induced by vasopressin/oxytocin-type neuropeptides, which are known to play a role in muscle regulation across various species. Prior research has characterized these signaling pathways in vertebrates, but there is limited understanding of how these mechanisms operate in invertebrates. This study is significant as it explores these pathways in the sea cucumber, contributing to the broader understanding of muscle contraction evolution across Bilateria.
Methods
The study utilized heterologous cell systems and in vitro pharmacological experiments to investigate the signaling pathways involved in holotocin-induced contraction of the longitudinal muscle of the body wall in Apostichopus japonicus. Specific doses and durations were not reported in the abstract.
Results
Holotocin induced a two-phase contraction in the longitudinal muscle of the body wall, characterized by an initial rapid phasic contraction followed by a sustained tonic contraction. The activation of a Gαq-dependent pathway was identified as a key mechanism in this process.
Interpretation
The findings reveal both similarities and differences in the signaling pathways mediating muscle contraction between invertebrates and vertebrates. While the study identifies significant pathways, the clinical relevance remains uncertain due to the lack of in vivo data and the focus on a single species, which may limit broader applicability.
Key findings
- Holotocin induced an initial rapid phasic contraction followed by a sustained tonic contraction.
- The contraction was mediated by the activation of a Gαq-dependent pathway.
- Phospholipase C was activated, leading to the hydrolysis of phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-trisphosphate and diacylglycerol.
- Increased intracellular Ca<sup>2+</sup> was triggered by inositol 1,4,5-trisphosphate release from intracellular stores.
- Depletion of intracellular Ca<sup>2+</sup> did not activate store-operated Ca<sup>2+</sup> entry.
Limitations
- In vitro experiments may not replicate in vivo conditions.
- Findings are specific to Apostichopus japonicus and may not generalize.
- No quantitative results reported in the abstract.