16 Intro to Cardiac Electrophysiology Flashcards
inward rectifier K currents work better at what membrane potential
more negative Vm
effective refractory period
too many Na channels still inactive for AP
inward current would be too small to spread to neighbors
are mostly depolarized by Ca2+ current rather than Na+ current
nodal cells(SA, AV)
describe adenosine/acetylcholine effects on nodal cells
- *act on M2 receptors **
- decreases cAMP, pacemaker(funny) current initiates at more negative/later potentials
- decreased PKA activity means less Ca current
act on IKAdo/IKACh directly
- increase K efflux making APs take longer
describe NE modulation of nodal cells
- *increases cAMP**
- makes pacemaker current initiate sooner during repolarization
- indirectly activates Ca channels via PKA prodution
pacemaker current
Na and K; Na predominates allowing eventual threshold/AP generation
strategies for interrupting arrhythmias
increase threshold(decrease Na current)
extend refractory period(increase AP duration, decrease K current)
EAD vs DAD
EAD appear during normal repolarization prior to complete repolarization
- most common in prolonged QT
DAD occur after max hyperpolarization
- occur with high intracellular calcium(digitalis)
blocking of hERG channels is associated with what pathology?
long QT syndrome
hERG channels are K channels; less K current means longer time to repolarize