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Prerequisite basic sciences
Calcium channel blockers
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Calcium entry blockers, or calcium channel blockers - CCBs for short - are vasodilators, or medications that promote dilation of blood vessels. These medications are mainly used to treat hypertension, or high blood pressure, and angina pectoris, which is a pain caused by reduced blood flow to the heart muscle. Now, by definition, blood pressure is the force that blood exerts on the walls of blood vessels and it’s basically what keeps blood flowing and perfusing tissues to deliver oxygen and nutrients. Hypertension happens when this pressure is higher than it should be. In most cases, the cause is unknown.
But basically, we can do a number of things to help lower the blood pressure. First, we can decrease the heart rate or the myocardial contractility, so the heart pumps less blood into the blood vessels. In other words, diminish the amount of blood that exerts force upon the same area. Or, we can vasodilate the peripheral blood vessels, which increases the area for the same amount of liquid that exerts force. Angina, on the other hand, is a type of chest pain caused by insufficient oxygen supply to the myocardium to meet its demand. Generally, the underlying cause is the presence of atheromatous plaques in the coronary arteries which decreases the blood flow to the heart. So, to help diminish the symptoms, it’s important to decrease the oxygen demand of the heart, again by decreasing heart rate or myocardial contractility; and increasing the oxygen supply by vasodilating the coronary arteries.
Now, let’s look at how calcium channels affect heart function. First off, the heart rate depends on the rate that the pacemaker cells in the sinus and atrioventricular node generate action potentials. These action potentials start automatically when sodium channels slowly let in a stream of sodium ions, which causes the membrane potential of the pacemaker cells to become more positive. When this reaches the threshold membrane potential, it’s the cue for voltage-gated calcium channels to open, allowing a large influx of calcium ions, which depolarizes it further. Then, these calcium channels close and potassium channels open to let potassium out of the cell, so the membrane potential goes back down, or repolarizes. Now, each cycle of depolarization and repolarization represents a single heartbeat, so how fast this process repeats in one minute determines the heart rate.
Calcium channel blockers (CCBs) are a class of drugs that cause vasodilation, and are mainly used to treat high blood pressure and angina pectoris. CCBs block calcium flow into the smooth muscle cells of your blood vessels, resulting in vasodilation and reduced blood pressure. They also work on cardiac muscle cells to reduce contractility and abnormally increased heart rate.
CCBs are grouped into two main types; dihydropyridines and non-dihydropyridines. Dihydropyridines mainly cause vasodilation and so are used to treat hypertension and angina. Examples of dihydropyridines include amlodipine, nicardipine, and nifedipine). The non-dihydropyridines target the heart muscle cells and decrease the heart rate and contractility. They are usually used to treat tachyarrhythmias, but also angina, because by reducing the heart rate and contractility, they bring down cardiac demand. Examples of non-dihydropyridines include diltiazem and verapamil. CCBs are typically well-tolerated, but they can cause certain side effects, such as dizziness, lightheadedness, and swelling of the ankles or legs.
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