Drugs Modifying Cardiac Rate and Force Flashcards
The ‘funny’ current, If, conducts what ions and in what direction
Na+
K+
inward
The background sodium current (Ib) conducts what ions and in what direction
Na+
inward
The transient calcium current (ICaT) conducts what ions and in what direction
Ca++
inward
The long calcium current (ICaL) conducts what ions and in what direction
Ca++
inward
The delayed rectifier potassium current (IK) conducts what ions and in what direction
K+
outwards
During phase 4 of action potential in the SA and AV nodes, what channels are acting.
Na+, background sodium current (Ib)(inward)
Ca++, transient calcium current (ICaT)(inward)
K+ (normally allow K to flow out of cell – turn off -> less of a hyperpolarising influence, contributes to pacemaker potential)
Delayed rectifier potassium current (IK)
(IF) Funny channel – allows sodium ions to move into cell (activated by hyperpolarisation)
During phase 0 (upstroke) of action potential in the SA and AV nodes, what channels are acting?
ICaL open
opening of voltage activated Ca++ channels (NOT Na+ channels)
*Calcium channels open more slowly than Na+ channels
During phase 3 (upstroke) of action potential in the SA and AV nodes, what channels are acting and how does this affect the cell?
IK open
Allows potassium to move out of cell
Inside of cell relatively negative
Head back to negative membrane potential
In atrial and ventricular myocytes of the heart, what channels control the action potential and how?
IK1 - inward rectifier potassium current (Outward)
INa - sodium current (Inward)
Ito - transient outward potassium current (Outward)
ICaL - long calcium current (inward)
IK - delayed rectifier potassium current (Outward)
Describe phase 4 of an action potential in a myocyte
resting membrane potential
at diastolic potential
horizontal on an action potential graph
IS STEADY ~-90mV
