Verapamil

Verapamil inhibits L-type calcium channels by binding to a specific area of their alpha-1 subunit, Cav1.2, which is highly expressed on L-type calcium channels in vascular smooth muscle and myocardial tissue where these channels are responsible for the control of peripheral vascular resistance and heart contractility. Calcium influx through these channels allows for the propagation of action potentials necessary for the contraction of muscle tissue and the heart's electrical pacemaker activity. Verapamil binds to these channels in a voltage- and frequency-dependent manner, meaning affinity is increased 1) as vascular smooth muscle membrane potential is reduced, and 2) with excessive depolarizing stimulus.

Verapamil's mechanism of action in the treatment of angina and hypertension is likely due to the mechanism described above. Inhibition of calcium influx prevents the contraction of vascular smooth muscle, causing relaxation/dilation of blood vessels throughout the peripheral circulation - this lowers systemic vascular resistance (i.e. afterload) and thus blood pressure. This reduction in vascular resistance also reduces the force against which the heart must push, decreasing myocardial energy consumption and oxygen requirements and thus alleviating angina.

Electrical activity through the AV node is responsible for determining heart rate, and this activity is dependent upon calcium influx through L-type calcium channels. By inhibiting these channels and decreasing the influx of calcium, verapamil prolongs the refractory period of the AV node and slows conduction, thereby slowing and controlling the heart rate in patients with arrhythmia.

Verapamil's mechanism of action in the treatment of cluster headaches is unclear, but is thought to result from an effect on other calcium channels (e.g. N-, P-, Q-, or T-type).

Verapamil is known to interact with other targets, including other calcium channels, potassium channels, and adrenergic receptors.