Figure 4.

Cardiac muscle contraction and changes with exercise. (A) Cardiac muscle contraction can occur as a consequence of calcium entry through L-type calcium channels, which activate ryanodine receptor (RyR) channels in the SR. Alternatively, β-adrenergic receptors on the cell membrane lead to activation of adenylyl cyclase (AC), which stimulates PKA. This can promote contraction by phosphorylating RyR and L-type calcium channels or relaxation by phosphorylating the SERCA pump inhibitor phospholamban. (B) Changes with exercise lead to an activation of the PI3K/Akt pathway, and a down-regulation of NFAT and calcinurin.