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Contraction Mechanism

Contraction Mechanism. Actin and myosin interact via to the sliding filament mechanism Resting State Actin bound by caldesmon Myosin light chain (MLC) dephosphorylated Intracellular [Ca 2+ ] low Rise in intracellular Ca 2+ triggers contraction

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Contraction Mechanism

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  1. Contraction Mechanism • Actin and myosin interact via to the sliding filament mechanism • Resting State • Actin bound by caldesmon • Myosin light chain (MLC) dephosphorylated • Intracellular [Ca2+] low • Rise in intracellular Ca2+ triggers contraction • Ca2+ enters from the extracellular space (some from SR) • Increase in [Ca2+ ]caused by: • Excitation by neurotransmitters (extracellular Ca) • Hormonal signaling via receptors & 2nd messengers (SR Ca) • Ca flux can be inhibited by various inhibitory stimuli – hormonal & neuronal

  2. Regulation of SM Contraction Actin

  3. Role of Ca2+ for Contraction • Ca2+ binds to calmodulin (Cam) • Ca-Cam binds to & activates myosin light chain kinase (MLCK) • Ca-Cam binds to & inactivates caldesmon • Active caldesmon binds actin • Ca-Cam-inactivated caldesmon can’t bind actin • The free actin is available for myosin to bind • Activated MLCK phosphorylates myosin head region allowing cross bridges with actin to form

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