Action Potentials/Drugs Flashcards
(9 cards)
What drug fits into both the II and III channel blocker categories?
Sotalol.
Describe the phases of a myocyte action potential.
Phase 0: Rapid depolarisation. Na+ active channels open and Na+ rapidly flows into the cell.
Phase 1: Na+ channels close causing a short dip.
Phase 2: K+ channels are open allowing K+ out. Ca2+ channels are open allowing Ca2+ in, causing a plateau.
Phase 3: Ca2+ channels close so the cell rapidly decreases in voltage. Repolarisation.
Phase 4: Cell is ready for the next action potential cycle.
Describe the phases of the SA node action potential.
Phase 0: Depolarisation. Less rapid than in a myocyte action potential due to lack of large Na+ channels. Ca2+ L-type voltage-gated channels open and Ca2+ moves into cell.
Phase 3: Repolarisation. Ca2+ channels shut and voltage-gated K+ channels open. K+ moves out the cell.
Phase 4: HCN ‘funny current I2’ channels are open, facilitating the next AP.
Describe the effects of class Ia channel blockers and name an example.
Ia: Fast sodium channel blockers. Immediate effect on phase 0. Prolongs AP. Procainamide, Quinidine, Disopyramide.
Describe the effect of Ib channel blockers and name one.
Sodium channel blockers that shorten the AP. It has a weak effect on phase 0. Lidocaine, Mexiletine, Tocainide.
Describe the effects of Ic channel blockers and name one.
Slow sodium channel blockers. Strongest effect on phase 0. Flecainide, Propafenone.
What class of channel blockers are beta blockers and what effect do they have on the ECG and AP?
Class II. They increase the PR interval and prolong repolarisation at the AV node.
Describe the effect of class III channel blockers and name one.
Potassium channel blockers extend the duration of phase 0. Examples include Amiodarone and Sotalol.
Describe the effect of class IV channel blockers on the AP and the ECG and name one.
Calcium channel blockers prolong repolarisation at the AV node and increase the ERP. They increase the PR interval. Verapamil and Diltiazem.
