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Cardiac Myocyte Physiology

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Topic updated on 06/12/17 8:30am

Overview
 

 
Introduction
  • Excitation-contraction coupling 
    • coupling of action potential to contraction of cardiac myocyte:
      • cardiac action potential depolarizes cardiac myocyte cell membrane
      • L-type voltage-gated Ca2+ channels in cardiac myocyte cell membrane open
        • aka dihydropyridine receptors
        • Ca2+ conductance increases in phase 2 (plateau) of cardiac action potential
      • inward Ca2+ current increases intracellular Ca2+
        • triggers calcium-induced calcium release
          • in response to increase in intracellular Ca2+, Ca2+ release channels in sarcoplasmic reticulum membrane open
            • aka ryanodine receptors
            • further increase intracellular Ca2+ levels
          • calcium-induced calcium release amplifies intracellular Ca2+ signal
      • intracellular Ca2+ binds troponin
        • induces a conformational change that removes tropomyosin inhibition of actin-myosin interaction
      • actin and myosin bind and cross-bridge cycling produces cardiac muscle tension
  • Relaxation
    • cardiac muscle relaxation and cardiac myocyte cell membrane repolarization occur when intracellular Ca2+ levels return to resting levels  
    • mechanisms of intracellular Ca2+ clearance
      • Na+/Ca2+ exchanger
        • Na+/Ca2+ exchanger (1 Ca2+ out, 3 Na+ in) pumps Ca2+ out of cardiac myocyte
          • Na+/K+ ATPase (3 Na+ out, 2 K+ in) in cardiac myocyte cell membrane establishes Na+ gradient that drives Na+/Ca22+ exchanger
      • Ca2+ ATPase
        • pump in cardiac myocyte cell membrane
        • Ca2+ ATPase pumps Ca2+ out of cardiac myocyte
      • Ca2+ ATPase
        • pump in sarcoplasmic reticulum membrane
        • Ca2+ ATPase pumps Ca2+ into sarcoplasmic reticulum


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Qbank (1 Questions)

TAG
(M1.CV.101) A scientist observes a myocyte beating in cell culture. Which step is a necessary component of relaxation for this cell? Topic Review Topic

1. Influx of sodium ions
2. Efflux of potassium ions
3. Influx of calcium ions from the sacroplasmic reticulum
4. Influx of calcium ions from outside the myocyte
5. Efflux of calcium ions

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