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#calcium ion

10 public questions tagged with this topic.

Regeneration -ll

Which ion is primarily involved in sperm activation in sea urchins?

Sea urchin sperm remain immotile in testes due to low pH and high CO2, then activate upon spawning into alkaline seawater. Egg jelly peptides speract and resact bind receptor guanylate cyclase on flagellar membrane, elevating cGMP, opening K+ channels, hyperpolarizing membrane, and activating Na+/H+ exchanger raising intracellular pH. Alkalization triggers CatSper channels opening causing calcium influx. Calcium pulses transform flagellar beat from symmetric low-amplitude to asymmetric high-amplitude turning events, accelerating respiration and preparing acrosomal exocytosis. Thus calcium acts as central second messenger linking chemotactic sensing to motility activation and readiness for fertilization.

Ref: NCBI Bookshelf, Molecular Biology of the Cell, Chapter 21: Sperm chemotaxis and CatSper-mediated Ca2+ influx in sea urchin.

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Sea urchin -l

Which ion is primarily involved in sperm activation in sea urchins?

Sea urchin sperm activation and chemotaxis involve dramatic intracellular ion fluxes coordinating motility. Egg jelly peptides like resact bind receptor guanylate cyclase localized on flagellar membrane, raising cGMP that opens K+ selective channels hyperpolarizing membrane, then Na+/H+ exchanger SLC9C1 raises intracellular pH activating dynein motor. Crucially Ca2+ influx through CatSper-associated channels in flagellum triggers increased asymmetric beating and acrosome reaction exocytosis. Intracellular Ca2+ oscillations also regulate turning behavior during chemotactic navigation toward egg. While K+, Na+, Mg2+ modulate excitability, Ca2+ acts as central second messenger orchestrating flagellar beat changes and secretory events.

Ref: Kaupp et al., Nature Reviews Mol Cell Biol 2008, Sperm chemotaxis and Ca2+ signaling in sea urchins.

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Membrane Transportation

Which ion is transported into the sarcoplasmic reticulum (SR) by SERCA?

Muscle contraction cycle requires rapid increase and decrease of cytosolic free calcium. At rest calcium about 100 nanomolar maintained by pumps and buffering proteins. Depolarization opens Cav1.1 dihydropyridine receptors mechanically coupled to RyR1 ryanodine receptors in skeletal muscle releasing calcium stored at millimolar total bound to calsequestrin in sarcoplasmic reticulum terminal cisternae, raising cytosolic calcium to ten micromolar activating troponin and cross bridge formation. For relaxation SERCA pump, sarco endoplasmic reticulum Ca2+ ATPase, abundantly expressed up to 70 percent of SR protein, actively resequesters calcium. It is 110 kilodalton P-type ATPase with ten transmembrane helices, two calcium binding sites high affinity cytosolic facing, ATP driven phosphorylation at Asp351 forming E1P Ca2+ occluded, transition to E2P low affinity lumenal releasing, two calcium per ATP transported against about 10,000 fold gradient. Thapsigargin irreversible inhibition depletes SR stores triggering ER stress. Plasma membrane Ca2+ ATPase PMCA and Na+/Ca2+ exchanger NCX supplement, but bulk reuptake into reticular store mediated by SERCA.

Ref: Toyoshima et al., Nature, SERCA Ca2+ ATPase Structure and Sarcoplasmic Reticulum Calcium Transport.

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Cytoskeleton

Which ion plays a crucial role in triggering muscle contraction?

Triggering of all muscle types converges on transient elevation of calcium as intracellular messenger linking excitation to contraction coupling electrical and mechanical events effectively. Resting cytosolic calcium held near 100 nanomolar by SERCA pumps actively sequestering calcium in sarcoplasmic endoplasmic reticulum lumen. Action potential propagating along sarcolemma and T tubules activates voltage gated L type channels physically coupled to ryanodine receptors in striated muscle causing explosive calcium release raising concentration to 10 micromolar in microdomains near thin filaments. Calcium binds to EF hand motifs: troponin C in skeletal cardiac exposing myosin binding sites on actin via tropomyosin movement and calmodulin in smooth muscle activating myosin light chain kinase phosphorylating regulatory light chain. Sodium influx initiates excitation but does not directly activate contractile proteins potassium and magnesium maintain electrochemical gradients and serve as ATP Mg cofactor. Rapid pump mediated calcium reuptake ends signal making calcium ideally suited for rapid reversible control of force and speed of contraction.

Ref: Alberts et al., Molecular Biology of the Cell, Chapter 15 – Calcium ion as crucial trigger for muscle contraction.

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