Ryanodine receptor calcium channels and their partners as drug targets.

Ryanodine receptors (RyRs) are high conductance intracellular cation channels that release calcium ions from stores such as the endoplasmic reticulum and sarcoplasmic reticulum. Although RyRs are expressed in many cell types, their roles have only been extensively characterised in tissues in which they are abundant: RyR1 is essential for excitation-contraction coupling in skeletal muscle; whereas RyR2 is required for the analogous signal transduction pathway in heart. Defects in RyR1 cause malignant hyperthermia and a spectrum of myopathies in skeletal muscle; whereas RyR2 dysregulation can result in fatal cardiac arrhythmias and is involved in heart failure. Altered RyR gating has been implicated in a range of other diseases, including epilepsy, neurodegeneration, pain and cancer. RyRs interact with a range of toxic substances, providing insights into their functional and structural properties. Consequently, these channel complexes represent potential therapeutic targets for treatment of numerous diseases. Furthermore, strategies for combating multicellular parasites and agricultural pests could exploit pharmacological differences between their RyRs and those of vertebrates. However, available pharmacological tools for manipulation of RyR gating are generally unsuitable for clinical, veterinary or agricultural use, owing to their lack of selectivity, inappropriate solubility in the aqueous or lipid environment, or generation of side-effects. The expression, subcellular distribution and gating of RyRs is modified by a wide variety of cellular proteins, some of which are expressed in a developmentally or tissue-restricted manner. This commentary examines the possibility of manipulating the expression and function of such proteins in order develop new drugs acting on RyR channel complexes.