Actin-myosin interactions in cardiac contraction
Cardiac contraction is brought about
by interactions between actin in the thin filament and myosin
cross‐bridges that project from the thick filament.
A, In relaxed muscle, where troponin C (TnC) is not bound to
calcium, the “relaxed” conformation of the troponin complexes and
tropomyosin prevents actin in the thin filament from interacting
with the myosin cross‐bridges. As a result, actin is
unable to convert the chemical energy of the ATP bound to the
myosin cross‐bridges into mechanical work.
B, In active muscle, Ca2+ bound to
TnC has shifted the troponin complexes and tropomyosin to an
“active” conformation that enables actin to interact with the
myosin cross‐bridges. Release of chemical energy when
actin stimulates hydrolysis of myosin‐bound ATP enables
the cross‐bridges to “row” the thin filaments toward the
center of the sarcomere. TnI—troponin I; TnT—troponin T.
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