Calcium is a universal second messenger regulating different biological functions from muscle contraction and neuronal excitability, to gene transcription and cell death. Physiologically, Ca2+ signals result both from the release of Ca2+ from intracellular stores as well as influx from the extracellular environment, via the opening of channels on the plasma membrane. In skeletal muscle, Ca2+ regulates contraction and relaxation and alterations in its intracellular concentration can lead to several neuromuscular disorders. Investigations carried out during the past decade have shown that in more than 50% of the cases, Central Core Disease, Multi-minicore disease and Malignant Hyperthermia are linked to point mutations in the gene encoding the skeletal muscle sarcoplasmic reticulum calcium release channel ryanodine receptor (RyR1), which is a key protein involved in releasing the calcium from the sarcoplasmic reticulum after plasma membrane depolarization. There are three isoforms of the ryanodine receptor which are expressed in different tissues; type 1 is preferentially expressed in skeletal muscles but recent data has shown that it is also expressed in some areas of the central nervous system as well as in cells of the immune system, specifically B-lymphocytes and dendritic cells. In the latter cell type, Ca2+ release through the ryanodine receptor leads to dendritic cell maturation, an important step underlying activation of the immune system to foreign antigens. These results imply that mutations in the ryanodine receptor gene will lead to alterations of Ca2+ homeostasis not only in skeletal muscle, but also in dendritic cells and B-lymphocytes, and thus will affect some aspects of the immune system. The aims of this project are to study the impact on the immune system of a mutation in the ryanodine receptor gene linked to Malignant Hyperthermia/Central Core Disease by studying the functions of dendritic cells/B-lymphocytes obtained from the Y522S ryanodine receptor knock in animal model. We will also continue our studies on the functional properties of muscle cells from patients with Central Core disease, Multi-mini core disease, Malignant Hyperthermia harbouring endogenous mutations in genes encoding for proteins involved in Ca2+ homeostasis by monitoring both Ca2+ homeostasis as well as Ca2+-dependent downstream events such as activation of nitric oxide synthase and the subcellular distribution of transcription factors, which may be affected by alterations of normal Ca2+ homeostasis.