Cardiac Electrophysiology - Myocardial Cells Flashcards
what controls resting potential in fast response cardiac cells?
high conductance through unique K channel
why is fast response K channel unique?
it closes when cell depolarizes
what causes upstroke of AP in fast response?
fast Na channels
what causes plateau of AP in fast response?
Ca channels
how does repolarization occur in fast response cells?
Ca channels inactivate, and slow K channel opens
when does slow K channel open?
doesnt open until cell has been depolarized for a long time
what cells do fast response cardiac aP?
- atrial myocytes
- ventricular myocytes
- purkinje conducting fibers
what cells do slow response cardiac AP ?
- SA node
2. AV node
which AP has a plateau?
atria/ventricle
how do cardiac cells prevent tetanic contraction?
duration of ventricular muscle AP and its effective refractory period is about as long as mechanical event (so unlikely to get another AP)
what types of K channels exist in cardiac resting potential
- voltage gated (slower or faster , longer or shorter)
- channels regulated by NT or hormones
- channels sensitive to intracellular metabolism like ATP
which K channel causes efflux of K through a voltage gated channel to hyperpolarize the cell?
iK1 (inwardly rectifying K current)
what controls fast upstroke of depolarization?
Na influx
what controls rapid partial repolarization spike?
Na channels closing
what controls plateau phase?
Ca influx
what controls repolarization phase
Ca channels close, iK channel opens, then iTO channels, then iK1
what controls membrane resting potential
iK1
when do iK1 channels open?
when cell is repolarizing, not when cells are depolarized
when does phase 0 end?
Na conductance drops because h gate closes (inactivation)
what causes phase 0
opening of fast Na channels
what causes phase 1
closing of Na channels, and transient K current iTO
what causes phase 2?
sustained Ca current through voltage gated channels
describe K conductance during phase 2
conductance drops because iK1 channels are closed, but some K current
what terminates plateau?
delayed iK channels opening
what is effect of sympathetic innervation on cardiac
B1 receptor effects via cAMP increase, increases Ca, increases force
PSNS effect on cardiac muscle
muscarinic receptor via cAMP decrease, decreases Ca, decrease force
what helps control active force in cardia cells?
calcium influx that controls Ca release from SR (inotropic state)
what occurs if Ca is modified in cardiac cell?
modifies SR release of Ca, which changes AP and force
what causes phase 3 repolarization?
Ca channels closing, iK delayed rectifying K channels opening to increase K current, then iTO opens K and Cl briefly, and then iK1 comes back.
what is the “voltage clamp”
iK1 channels hyperpolarizing the cell
what channel dominates resting membrane potential?
iK1
