Ryanodine
Encyclopedia
Ryanodine is a poisonous alkaloid
Alkaloid
Alkaloids are a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids...

 found in the South American plant Ryania speciosa (Flacourtiaceae
Flacourtiaceae
Flacourtiaceae is a defunct family of flowering plants whose former members have been scattered to various other families, mostly to Achariaceae, Samydaceae, and Salicaceae. It was so vaguely defined that hardly anything seemed out of place there and it became a dumping ground for odd and anomalous...

). It was originally used as an insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...

.

The compound has extremely high affinity to the ryanodine receptor
Ryanodine receptor
Ryanodine receptors form a class of intracellular calcium channels in various forms of excitable animal tissue like muscles and neurons...

, a group of calcium channel
Calcium channel
A Calcium channel is an ion channel which displays selective permeability to calcium ions. It is sometimes synonymous as voltage-dependent calcium channel, although there are also ligand-gated calcium channels.-Comparison tables:...

s found in skeletal
Striated muscle
Striated muscle tissue is a form of fibers that are combined into parallel fibers. More specifically, it can refer to:* Cardiac muscle .* Skeletal muscle* Branchiomeric muscles...

 and heart muscle cells. It binds with such high affinity to the receptor that it was used as a label for the first purification of that class of ion channel
Ion channel
Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...

s and gave its name to it.

At nanomolar concentrations, ryanodine locks the receptor in a half-open state, whereas it fully closes them at micromolar concentration. The effect of the nanomolar-level binding is that ryanodine causes release of calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 from calcium stores in the sarcoplasmic reticulum leading to massive muscular contractions. This is true for both mammals and insects.
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