What is "ruthenium red"

n. An inorganic dye used in histology to stain aldehyde-fixed mucopolysaccharides

The inorganic dye ammoniated ruthenium oxychloride, also known as ruthenium red, is used in histology to stain aldehyde fixed mucopolysaccharides.

Ruthenium red (RR) has also been used as a pharmacological tool to study specific cellular mechanisms. Selectivity is a significant issue in such studies as RR is known to interact with a large number of proteins. These include mammalian ion channels ( CatSper1, TASK, RyR1, RyR2, RyR3, TRPM6, TRPM8, TRPV1, TRPV2, TRPV3, TRPV4, TRPV5, TRPV6, TRPA1, mCa1, mCa2, CALHM1) TRPP3, a plant ion channel, Ca-ATPase, mitochondrial Ca uniporter, tubulin, myosin light-chain phosphatase, and Ca binding proteins such as calmodulin. Ruthenium red displays nanomolar potency against several of its binding partners (e.g. TRPV4, ryanodine receptors,...). For example, it is a potent inhibitor of intracellular calcium release by ryanodine receptors (Kd ~20 nM). As a TRPA1 blocker, it assists in reducing the airway inflammation caused by pepper spray.

RR has been used on plant material since 1890 for staining pectins, mucilages, and gums. RR is a stereoselective stain for pectic acid, insofar as the staining site occurs between each monomer unit and the next adjacent neighbor.