16 Cardiac AP

Myocyte AP

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  • at rest, pumps maintain ion distribution

  • connected via gap junction

  • if 1 depolarizes with positive ions inside, some positive go to 2, 2 depolarizes

  • phase 4: myocyte at rest, -85

  • phase 0: voltage begins to rise from positive ions entering via gap junction, Na channels open, further rise positive charges, positive loop

  • phase 1: voltage become positive, Na channels close, K open and leak out, lower voltage

  • phase 2: competing Ca in and K out, cancelling one another = plateau

  • phase 3: Ca close, only K

  • -85 maintained by inward rectifier channels: K out

  • Soloist: class I antiarrhythmics

  • Soloist holding peanut butter jar: class I antiarrhythmics block sodium channels (phase 0)

  • Soloist tipping mic stand: class I antiarrhythmics decrease the slope of the phase 0 upstroke (slows conduction of the cardiac AP)

  • Ca ion trigger mechanical contraction of myocyte

  • excitation-contraction coupling: Ca connects electrical activity and mechanical activity of myocytes

  • Pushing away the curtain: class III antiarrhythmics block K+ channels prolonging phase 2 and 3 of the cardiac action potential -> prolonged refractory period

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  • No Ca involvement

  • each cell individually depolarized by neuron

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Pacemaker AP

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  • slightly higher resting voltage > -85

  • no plateau

  • phase 4: slowly drifts upward, funny current allow Na in

  • phase 0: - 40 threshold, Ca open, inward Ca

  • phase 3: above 0, Ca close, K open

  • AV node, same shape, phase 4 slower, longer to reach threshold, usually depolarized by SA signal before threshold

  • fast Na need -85 to function: fewer inward rectifier K (-85 resting membrane) > resting always above -60 > fast Na does not work

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  • slow AV: delay conduction from atrium to ventricle

  • slow phase 0

  • block activated and inactivated Ca channels, not resting channels. Work more on tissues fire more frequently and exclusively activated by Ca current

  • Notes: non-dihydropyridines (e.g. diltiazem, verapamil) treat arrhythmias by blocking Ca2+ current in the SA and AV nodes

  • Disconnected bottom: non-dihydropyridine CCBs decrease atrioventricular conduction

  • Duet: Class 2 antiarrhythmics

  • Muted beta bugle: beta blockers (class 2 antiarrhythmics)

  • notes: beta blockers treat arrhythmias by blocking sympathetic input to the SA and AV nodes

  • Torn band camp: beta blockers decrease cAMP

  • Crushed calci-YUM ice cream cartons: decreased cAMP leads to closure of membrane calcium channels

  • Sliding up the keys: beta blockers prolong phase 4 of the nodal action potential -> decreased pacemaker activity, prolonged conduction time and refractory period.

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  • Swing dancing: adenosine (a purine nucleoside with antiarrhythmic properties)

  • Purine shaped gate: adenosine is a purine nucleotide

  • A1 Swing: adenosine activates inhibitory A1 receptors on the myocardium and at the SA and AV nodes

  • Falling calci-yum ice cream: activation of A1 receptors suppresses inward Ca2+ current (hyperpolarization, suppressed Ca2+ dependent AP

  • Banana flying out of cup: activation of A1 receptors increases outward K+ current (hyperpolarization, suppressed Ca2+ dependent AP)

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