Sarcoplasmic reticulum calcium-handling system (SR Ca2+ handling system)

The sarcoplasmic reticulum (SR) calcium-handling system is a specialized protein network in striated muscle cells that regulates the rapid cycling of calcium ions (Ca2+) required for contraction and relaxation. This system comprises several key functional units: the Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump, which actively transports Ca2+ from the cytosol into the SR lumen; the Ryanodine Receptor (RyR), which serves as the primary Ca2+ release channel; and a suite of luminal Ca2+-binding proteins, most notably Calsequestrin (CASQ), Sarcalumenin, and Histidine-rich calcium-binding protein (HRC), which buffer and store Ca2+ at high capacities. Proper coordination within this system is vital for excitation-contraction coupling; for instance, CASQ not only buffers Ca2+ but also modulates RyR activity in response to luminal Ca2+ levels. Pathological alterations in these proteins, such as SERCA downregulation or RyR leakiness, are central to the pathogenesis of heart failure, catecholaminergic polymorphic ventricular tachycardia (CPVT), and malignant hyperthermia. Consequently, the system is a major focus for drug development, with therapies like istaroxime targeting SERCA and dantrolene targeting RyR to restore calcium homeostasis and improve muscle function.

Other names

Sarcoplasmic reticulum Ca2+ binding systemSR calcium-buffering systemSR calcium-regulatory complexExcitation-contraction coupling machinery

SERCA activation, Ryanodine receptor inhibition, Ryanodine receptor activation, Calcium buffering modulation, SERCA inhibition