Verapamil, known as the brand names Calan, Isoptin, Tarka, and Verelan, is a non-dihydropyridine calcium channel blocker used in the treatment of angina, arrhythmia, and hypertension. It is used for the treament of vasopastic angina, unstable angina, chronic stable angina, treat hypertension, for the prophylaxis of repetitive paroxysmal supraventricular tachycardia,and atrial fibrillation or atrial flutter in combination with digoxin. It is normally given intravenously, so it has a rapid release with a short duration of action. Verapamil acts on smooth muscles and cardiac muscles. Excitation of cardiac muscle involves the activation of a slow calcium inward current that is induced by L-type slow calcium channels, which are voltage-sensitive, ion-selective channels associated with a high activation threshold and slow inactivation profile. L-type calcium channels are the main current responsible for the late phase of the pacemaker potential. Activation of L-type calcium channels allows the influx of calcium ions into the muscles upon depolarization and excitation of the channel. This is essential for the propogation of action potentials in the myocytes necessary for the contraction of the muscle tissue and the heart's electrical pacemaker activity. It is proposed that this cation influx may also trigger the release of additional calcium ions from intracellular storage sites. Electrical activity through the AV node is responsible for determining heart rate. This activity is dependent on calcium influx through L-type calcium channels. Therefore, the inhibition of L-type calcium channels, by verapamil, decreases the influx of calcium, which prolongs the refractory period of the AV node and slows conduction. This slows and controls the heart rate. Verapamil's mechanism of action in the treatment of cluster headaches is unclear, but is thought to be involved with its effect on calcium channels.

Verapamil Calcium Channel Cardiac Muscle Relaxation Pathway References