Walk through the sequence of events during excitation, contraction, and relaxation of cardiac muscle cells, including terms DHPR, RyR2, myoplasm, SR, troponin, thin filaments, SERCA2, terminal cisternae, longitudinal cisternae, calsequestrin, NCX Na+/Ca2+ exchanger, and PMCA.
- AP spreads into t-tubule system
- Ca2+ channel in t-membrane (DHPR) opens and allows entry of extracellular Ca2+
- Influx of Ca2+ activates RyR2 in SR membrane to cause a much larger flux of Ca2+ from SR into myoplasm
- Ca2+ activates contraction by binding to troponin on thin filaments, allowing actin-myosin cross-bridge cycling and contraction
- Ca2+ is removed from myoplasm by: 1) SERCA2 pumps located in longitudinal SR. Ca2+ diffuses within SR to terminal cisternae, where it binds to calsequestrin (low affinity, high capacity) and 2) NCX Na+/Ca2+ exchanger in junctional domains of plasma membrane and t-tubules and 3) PMCA pump in surface membrane (1 Ca2+ per cycle).