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Excitation-Contraction Coupling

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imissyou419's version from 2017-01-27 22:59

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Cardiac cell similarities to Skeletal AP on sacrolemma spreads to T-tubules, depolarizes it, and causes release of Ca2+ from SR, contraction similar: Ca2+ bind to troponin, troponin pulls tropomyosin off myosin binding sites, myosin attaches to actin and form cross bridge, powerstroke, sliding filament
Cardiac cell differences to Skeletalextracellular Ca2+ enters sacroplasm during depolarization of sacrolemma, extracellular Ca2+ can interact with SR to cause Ca2+-induced Ca2+ release from SR, instead of DHP receptor (voltage sensor) on T-tubule changing conformation, it is slow L-type Ca2+ channels
What are the 4 ways free intracellular Ca2+ can be increased by:1. depolarization induced Ca2+ influx from extracellular through L-type Ca2+ channels (DHP Ca2+ channels), 2. Extracellular Ca2+ can enter through Na+/Ca2+ exchanger, extracellular Ca2+ induced Ca2+ release, 4. intracellular Ca2+ induced Ca2+ release from SR
Does depolarization directly open ryanodine/Ca2+ channels on SR?Not sure, but Ca2+ does in cardiac muscle
DHP-Ryr Ca2+ release channels in Cardiac vs. SkeletalIn cardiac, DHP-Ryr are not physically linked, DHP are slow L-type Ca2+ channels; extracellular Ca2+ can directly cause contraction + cause Ca2+ induced Ca2+ release. In skeletal, DHP-Ryr are physically linked, DPH sensors depolarization and releases Ca2+; NO CA+ INDUCED CA2+ RELEASE
Why is extracellular Ca2+ important in cardiac cells?Extracellular Ca2+ small amount compared to released from SR but ESSENTIAL for triggering Ca2+ release from SR + maintains intracellular Ca2+ stores over long run (since Na+/Ca2+ exchanger normally putting Ca2+ out)
What are the 3 ways free intracellular Ca2+ decreased by:1. actively pumped back into SR by Ca2+ ATPase (80%), Ca2+ actively pumped outside by Ca2+ ATPase (5%), Na+/Ca2+ exchanger on sacrolemma pumps 3 Na+ in/1 Ca2+ out (15%)
Na+/Ca2+ exchanger on sacrolemmaNormally puts 3 Na+ in/ 1 Ca2+ out; reversed when: Na+ conc inside cell rises dramatically, membrane pot become + during depol
Why can there be no tetanus in heart?Contractile response begins after start of depol and lasts 250-300 ms because of plateau phase so it occupies most of absolute refractory period, so when AP ends, contractile response is pretty much done so cannot summate (different than motor unit because length of AP = 1-2 ms and contractile response = 100 ms so can have many APs hit before contractile response is over)
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