Cardiac muscles

[Ref: WG21:Chp3]

See Fast-response cardiac action potential for cardiac action potential

 

Some differences

• Very rich in mitochondria
• Transverse-tubular system is at Z lines

Intercalated disks

• Located at Z lines
• Gap junctions present
• Allow myocytes to act as a syncytium
• Provide strong cell-to-cell cohesion

 

Contraction

• Contractile response begins just after the start of the depolarisation
• Last about 1.5 times as long as the AP

 

Excitation-contraction coupling

Voltage change in membrane

--> Activation of dihydropyridine channels in the T-tubules

--> Influx of Ca2+ from ECF

--> Release of stored Ca2+ from SR via calcium release channels (ryanodine receptors)

--> Contraction initiated

Ca2+ from ECF alone is insufficient to induce contraction.