How do beta blockers affect cardiac action potential?

Beta-blockers decrease the rate of Vmax of the action potential, prolongs its duration as well as the effective refractory period. Drug-induced slowing of the heart rate with resulting decreases in myocardial oxygen requirements is desirable in patients with coronary artery disease.

What initiates ventricular action potential?

The beginning of the action potential, phase 0, specialized membrane proteins (voltage-gated sodium channels) in the cell membrane selectively allow sodium ions to enter the cell. This causes the membrane potential to rise at a rate of about 300 V/s.

Is propranolol an antiarrhythmic?

Propranolol exerts its antiarrhythmic effects in concentrations associated with beta-adrenergic blockade, and this appears to be its principal antiarrhythmic mechanism of action.

What are the two phases of the ventricular action potential?

The ventricular action potential is composed of four phases: phase 0 is depolarization, phase 1 is early repolarization, phase 2 is a plateau, phase 3 is rapid repolarization and phase 4 is the resting potential. The different phases depend on the opening and/or closure of specific ion channels.

Which phase of the ventricular myocyte action potential would you expect to be most affected by verapamil?

plateau phase
Calcium-channel blockers such as verapamil and diltiazem affect the plateau phase (phase 2) of the action potential. Potassium-channel blockers delay repolarization (phase 3) by blocking the potassium channels that are responsible for this phase.

Does propranolol cause bronchoconstriction?

The bronchospasm was severe in all three and in one patient resulted in respiratory arrest. Since the bronchospasm was relieved with discontinuation of propranolol and supportive bronchodilator therapy, the bronchospasm was believed to be caused by propranolol.

What are the two types of action potential in the heart?

The first type is characterized by a prominent phase 1 repolarization and a relatively negative plateau level. The second type resembles the action potential elicited in ventricular cells isolated from the same hearts. It shows little phase 1 repolarization and a relatively positive plateau level.

Is propranolol a vasodilator?

Since the drug blocks the vasodilator (β-receptor stimulating) effects of catecholamines without affecting the vasoconstrictor (α-receptor stimulating) property, propranolol should be expected to cause the vasocon-striction of the peripheral vessels.