Cardiac Muscle Cell Excitation and Contraction Flashcards
What are calcium channels dependent on?
Time-dependent
Voltage-dependent
What characterizes L-type calcium channels?
Long opening time, sensitive to dihydropyridines (DHPs) open at a more positive membrane potential -30 mV
What characterizes T-type calcium channels?
Short opening time, less ion conductance, insensitive to DHPs and open at a more negative MP -50 mV (found in atria pacemaker cells)
What do DHPs do to L-type channel?
Decreases its activity inhibit it
What causes spontaneous action potentials in cardiac tissue?
The SA node
What is calcium induced calcium release?
Calcium entering through the DHP (L-type) causes the RyR2 receptor to release more calcium from the sarcoplasmic reticulum
What is the difference in mechanism of RyR1 and RyR2 and DHP mechanism?
RyR1 is mechanically uncoupled by DHP
DHP always calcium into the cell which then activates RyR2
What troponin does calcium bind to?
Tn-C
What gives cardiac muscle its higher passive tension and length-tension curve?
The protein titin
What are mutations in titin associated with?
Hereditary myopathy
What effect does sympathetic stimulation have on titin?
Titin becomes phosphorylated and becomes more compliant and less resistance to diastolic filling
How does calcium affect myocytes?
It is a graded scale not all or nothing
What happens to velocity and force of contraction when there is greater preload/increased fiber length?
Increased velocity
Increased force of contraction
What happens to calcium channels when the myocytes are stretched?
It increases the sensitivity of the contractile apparatus to Ca2+ causing it to develop more tension and also opens more Ca2+ stretch channels
What is force-frequency relation?
Increases in HR increases the force of contraction up to high rates after which there is a negative effect
