Ryanodine receptors form a class of calcium channels in various forms of muscle. RyR1 is expressed in skeletal muscle, and RyR2 in myocardium. A third form, RyR3, is expressed more widely, but especially in the brainZucchi R, Ronca-Testoni S. The sarcoplasmic reticulum Ca²⁺ channel/ryanodine receptor: modulation by endogenous effectors, drugs and disease states. Pharmacol Rev 1997;49:1-51. PMID 9085308..

The receptors are named after the plant alkaloid ryanodine, to which they show affinity.

Physiology

---

Ryanodine receptors mediate the release of calcium from the sarcoplasmic reticulum, an essential step in muscle contraction.

Ryanodine receptors are similar to the InsP₃ receptor and stimulated to transport Ca²⁺ into the cytosol by recognizing Ca²⁺ on its cytosolic side, thus establishing a feedback mechanism; a small amount of Ca²⁺ in the cytosol near the receptor will cause it to release even more Ca²⁺ (calcium-induced calcium release/CICR).

RyRs are especially important in neurons and muscle cells. In heart and pancreas cells, another second messenger (cyclic ADP ribose) takes part in the receptor activation.

The localized and time-limited activity of Ca²⁺ in the cytosol is also called a Ca²⁺ wave. The building of the wave is done by

• the feedback mechanism of the ryanodine receptor and
• the activation of phospholipase C by Ca²⁺, which leads to the production of inositol triphosphate, which in turn activates the InsP₃ receptor.

Role in disease

---

RyR1 mutations are associated with malignant hyperthermia and central core disease. RyR2 mutations play a role in stress-induced polymorphic ventricular tachycardia (a form of cardiac arrhythmia) and ARVD. It has also been shown that levels of type RyR3 are greatly increased in PC12 cells overexpressing mutant human Presenilin 1, and in brain tissue in knockin mice that express mutant Presenilin 1 at normal levels, and thus may play a role in the pathogenesis of neurodegenerative diseases, like Alzheimer's disease.

The presence of antibodies against ryanodine receptors in blood serum has also been associated with myasthenia gravis.

Reference

---

External links

---

• (RyR1), (RyR2), (RyR3)

Récepteur de la ryanodine