Figure 1.

Cardiac intracellular Ca²⁺ is tightly regulated by several proteins. Efficient systolic contraction and diastolic relaxation is reliant on efficient Ca²⁺ handling through 5 main processes. (1) Diffusion of Ca²⁺ in to the cytosol via voltage-gated Ca²⁺ channels (DHPRs) located on the surface of the transverse-tubule (T-tubule); (2) Ca²⁺-induced-Ca²⁺-release from the ryanodine receptors (RyRs); (3) Binding of Ca²⁺ to troponin-C in the sarcomere, stimulating actin-myosin cross-linking; (4) Sequestration of Ca²⁺ back in to the sarcoplasmic reticulum via the important Ca²⁺ pump sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA2a); and (5) Expulsion of Ca²⁺ from the cell via sodium-calcium exchanger pumps (NCX). JP, junctophilins; PLB, phopholamban; ATP, ATP pump; 3Na⁺, sodium; K⁺, potassium.