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#calcium release

3 public questions tagged with this topic.

Regeneration -ll

What molecule initiates calcium release in egg cytoplasm after fertilization?

Egg cytoplasmic calcium rise is triggered by diffusible second messenger inositol 1,4,5-trisphosphate IP3 acting on endoplasmic reticulum calcium stores. IP3 binds ligand-gated IP3 receptors, tetrameric channels releasing sequestered calcium producing self-propagating wave due to calcium-induced calcium release. Upstream sperm factor activates Src-family kinase that phosphorylates and recruits phospholipase C gamma to membrane where it cleaves PIP2 into DAG and IP3. Cyclic AMP predominates in sperm chemotaxis signaling, diacylglycerol activates protein kinase C regulating Na+/H+ exchange, ATP fuels processes but does not gate calcium release directly; IP3 is immediate chemical trigger.

Ref: Molecular Biology of the Cell, Chapter 15: IP3-mediated calcium release via phospholipase C during egg activation.

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Sea urchin -l

What molecule initiates calcium release in egg cytoplasm after fertilization?

Egg activation calcium wave absolutely requires inositol trisphosphate-mediated release of endoplasmic reticulum calcium stores rather than extracellular influx. Phospholipase C enzyme introduced by sperm factor and activated endogenous PLCγ via Src family tyrosine kinases cleaves abundant phosphatidylinositol 4,5-bisphosphate residing in egg plasma membrane inner leaflet generating two potent second messengers: membrane-bound diacylglycerol activating protein kinase C and soluble inositol 1,4,5-trisphosphate (IP3) that diffuses rapidly to bind IP3 receptors on endoplasmic reticulum opening ligand-gated Ca2+ channels. Resulting localized Ca2+ efflux triggers further calcium-induced calcium release propagating global wave. cAMP, DAG alone, ATP do not directly liberate calcium from internal stores.

Ref: Whitaker & Irvine, Nature 1984, IP3 mediated calcium release; Gilbert Chapter 7: PLC-IP3 pathway.

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Cell Signaling GPCR Pathways - I

IP3 primarily causes release of Ca2+ from

Inositol 1,4,5-trisphosphate generated by phospholipase C diffuses through the cytosol and binds IP3-gated calcium channels on the endoplasmic reticulum. Channel opening releases stored Ca2+ into the cytosol, producing a rapid rise in free calcium that activates calmodulin-dependent enzymes and other calcium-sensitive effectors. The endoplasmic reticulum is therefore the primary source of IP3-mobilized calcium.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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