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#sarcoplasmic reticulum

8 public questions tagged with this topic.

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 perce

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

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

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Cytoskeleton

In skeletal muscle contraction, which protein regulates Ca2+ reuptake into the sarcoplasmic reticulum?

Relaxation requires rapid calcium clearance to restore resting state permitting cross bridge detachment and tropomyosin return to blocking. Sarcoplasmic reticulum calcium ATPase SERCA, family of P type ATPases with ten transmembrane helices and three cytoplasmic domains N P A, couples ATP hydrolysis to transport of two calcium ions per cycle from cytosol to SR lumen against concentration gradient 10,000 fold. In skeletal fast twitch SERCA1a constitutes 60 percent SR protein, in cardiac SERCA2a regulated by phospholamban PLN small inhibitor that reduces calcium affinity when dephosphorylated, p

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17: SERCA Ca2+-ATPase and Muscle Relaxation.

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