E-C coupling
EXCITATION-CONTRACTION COUPLING
Marie Nováková
DEFINITION
Events connecting electrical activity of the heart (depolarization
of sarcolemma), EXCITATION
and its mechanical response, CONTRACTION
Link between these events is Ca2+
FUNCTION
• Triggering of contraction
• Regulation of contraction force
KEY STRUCTURES / ORGANELLES / RECEPTORS
• Transverse tubules of sarcolemma (T-tubules)
• Sarcoplasmic reticulum (SR)
• Calcium channels:
DHPR (dihydropyridine receptor) in T-tubules/sarcolemma
RYR (ryanodine receptor) in SR
SARCOTUBULAR SYSTEM
FUNCTIONAL ORGANISATION of SARCOTUBULAR SYSTEM
RHABDOMYOCYTE CARDIOMYOCYTE
TRIAD DIAD
DHPR
T-tubuleterminal SR cistern terminal SR cistern T-tubule terminal SR cistern
RYR
Ca2+
Ca2+Ca2+
RHABDOMYOCYTE
DHPR RYR1 (voltage-gated)
„Mechanical“ relation between DHPR and RYR
sarcolemma
AP
terminal SR cistern terminal SR cistern
Ca2+
Calsequestrin = Ca2+ buffer
SERCA
SERCA- Sarcoplasmic
Endoplasmic Reticular
Ca2+-ATPase
Ca2+
10-4M
10-7M
[Ca2+]c
„Closed system“ of Ca2+ movement
CARDIOMYOCYTE
DHPR (in sarcolemma
and in T-tubules)
RYR2 (calcium-gated)
AP
10-5M
10-7M
[Ca2+]c
Calsequestrin = Ca2+ buffer
SERCA
Ca2+
Ca2+
ICa
CICR
(calcium-induced-calcium-release)
„Open system“ of Ca2+ movement
Strong dependence on [Ca2+]e !
ICa
ICa
Ca2+
ATPase
Na+/Ca2+
exchanger