Ryanodine Receptor - Physiology

Physiology

Ryanodine receptors mediate the release of calcium ions from the sarcoplasmic reticulum, an essential step in muscle contraction. In skeletal muscle, it is thought that activation occurs via a physical coupling to the dihydropyridine receptor, whereas, in cardiac muscle, the primary mechanism is calcium-induced calcium release from the sarcoplasmic reticulum.

It has been shown that calcium release from a number of ryanodine receptors in a ryanodine receptor cluster results in a spatiotemporally-restricted rise in cytosolic calcium that can be visualised as a calcium spark.

Ryanodine receptors are similar to the inositol trisphosphate (IP3) receptor, and stimulated to transport Ca into the cytosol by recognizing Ca on its cytosolic side, thus establishing a positive feedback mechanism; a small amount of Ca in the cytosol near the receptor will cause it to release even more Ca (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 Ca in the cytosol is also called a Ca wave. The building of the wave is done by

  • the feedback mechanism of the ryanodine receptor
  • the activation of phospholipase C by GPCR or TRK, which leads to the production of inositol trisphosphate, which in turn activates the InsP3 receptor.

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