Calcium channel blockers | |
---|---|
Drug class | |
Class identifiers | |
Use | hypertension, arrhythmia, cluster headache [1] |
ATC code | C08 |
External links | |
MeSH | D002121 |
Legal status | |
In Wikidata |
Calcium channel blockers (CCB), calcium channel antagonists or calcium antagonists [2] are a group of medications that disrupt the movement of calcium (Ca2+
) through calcium channels. [3] Calcium channel blockers are used as antihypertensive drugs, i.e., as medications to decrease blood pressure in patients with hypertension. CCBs are particularly effective against large vessel stiffness, one of the common causes of elevated systolic blood pressure in elderly patients. [4] Calcium channel blockers are also frequently used to alter heart rate (especially from atrial fibrillation), to prevent peripheral and cerebral vasospasm, and to reduce chest pain caused by angina pectoris.
N-type, L-type, and T-type voltage-dependent calcium channels are present in the zona glomerulosa of the human adrenal gland, and CCBs can directly influence the biosynthesis of aldosterone in adrenocortical cells, with consequent impact on the clinical treatment of hypertension with these agents. [5]
CCBs have been shown to be slightly more effective than beta blockers at lowering cardiovascular mortality associated with stroke, but they are associated with more side effects. [6] [7] Potential major risks however were mainly found to be associated with short-acting CCBs. [8]
Dihydropyridine (DHP) calcium channel blockers are derived from the molecule dihydropyridine and often used to reduce systemic vascular resistance and arterial pressure. Sometimes when they are used to treat angina, the vasodilation and hypotension can lead to reflex tachycardia, which can be detrimental for patients with ischemic symptoms because of the resulting increase in myocardial oxygen demand. Dihydropyridine calcium channel blockers can worsen proteinuria in patients with nephropathy. [9]
This CCB class is easily identified by the suffix "-dipine".
Phenylalkylamine calcium channel blockers are relatively selective for myocardium, reduce myocardial oxygen demand and reverse coronary vasospasm, and are often used to treat angina. They have minimal vasodilatory effects compared with dihydropyridines and therefore cause less reflex tachycardia, making it appealing for treatment of angina, where tachycardia can be the most significant contributor to the heart's need for oxygen. Therefore, as vasodilation is minimal with the phenylalkylamines, the major mechanism of action is causing negative inotropy. Phenylalkylamines are thought to access calcium channels from the intracellular side, although the evidence is somewhat mixed. [10]
Benzothiazepine calcium channel blockers belong to the benzothiazepine class of compounds and are an intermediate class between phenylalkylamine and dihydropyridines in their selectivity for vascular calcium channels. By having both cardiac depressant and vasodilator actions, benzothiazepines are able to reduce arterial pressure without producing the same degree of reflex cardiac stimulation caused by dihydropyridines.
While most of the agents listed above are relatively selective, there are additional agents that are considered nonselective. These include mibefradil, bepridil, flunarizine (BBB crossing), fluspirilene (BBB crossing), [11] and fendiline. [12]
Gabapentinoids, such as gabapentin and pregabalin, bind selectively to the α2δ protein that was first described as an integral part of voltage-gated calcium channels. These drugs do not directly block calcium channels [13] [14] but can alter the transport of functional calcium channels to the cell membrane and they also reduce the release of certain excitatory neurotransmitters. They are used primarily to treat epilepsy and neuropathic pain. [15] More recently, the α2δ-1 protein has been found to bind directly and to interact with certain glutamate receptors and to the interstitial protein thombospondin, independently from their action at calcium channels.
Ziconotide, a peptide compound derived from the omega-conotoxin, is a selective N-type calcium channel blocker that has potent analgesic properties that are equivalent to approximate 1,000 times that of morphine. It must be delivered via the intrathecal (directly into the cerebrospinal fluid) route via an intrathecal infusion pump. [16]
Naturally occurring compounds and elements such as magnesium have also been shown to act as calcium channel blockers when administered orally. [17]
Side effects of these drugs may include but are not limited to:
Mild CCB toxicity is treated with supportive care. Nondihydropyridine CCBs may produce profound toxicity, and early decontamination, especially for slow-release agents, is essential. For severe overdoses, treatment usually includes close monitoring of vital signs and the addition of vasopressive agents and intravenous fluids for blood pressure support. Intravenous calcium gluconate (or calcium chloride if a central line is available) and atropine are first-line therapies. If the time of the overdose is known and presentation is within two hours of ingestion, activated charcoal, gastric lavage, and polyethylene glycol may be used to decontaminate the gut. Efforts for gut decontamination may be extended to within 8 hours of ingestion with extended-release preparations.[ citation needed ]
Hyperinsulinemia-euglycemia therapy has emerged as a viable form of treatment. [24] Although the mechanism is unclear, increased insulin may mobilize glucose from peripheral tissues to serve as an alternative fuel source for the heart (the heart mainly relies on oxidation of fatty acids). Theoretical treatment with lipid emulsion therapy has been considered in severe cases, but is not yet standard of care.
Caution should be taken when using verapamil with a beta blocker due to the risk of severe bradycardia. If unsuccessful, ventricular pacing should be used. [25]
Research indicates ethanol is involved in the inhibition of L-type calcium channels. One study showed the nature of ethanol binding to L-type calcium channels is according to first-order kinetics with a Hill coefficient around 1. This indicates ethanol binds independently to the channel, expressing noncooperative binding. [26] Early studies showed a link between calcium and the release of vasopressin by the secondary messenger system. [27] Vasopressin levels are reduced after the ingestion of alcohol. [28] The lower levels of vasopressin from the consumption of alcohol have been linked to ethanol acting as an antagonist to voltage-gated calcium channels (VGCCs). Studies conducted by Treistman et al. in the aplysia confirm inhibition of VGCC by ethanol. Voltage clamp recordings have been done on the aplysia neuron. VGCCs were isolated and calcium current was recorded using patch clamp technique having ethanol as a treatment. Recordings were replicated at varying concentrations (0, 10, 25, 50, and 100 mM) at a voltage clamp of +30 mV. Results showed calcium current decreased as concentration of ethanol increased. [29] Similar results have shown to be true in single-channel recordings from isolated nerve terminal of rats that ethanol does in fact block VGCCs. [30]
Studies done by Katsura et al. in 2006 on mouse cerebral cortical neurons, show the effects of prolonged ethanol exposure. Neurons were exposed to sustained ethanol concentrations of 50 mM for 3 days in vitro. Western blot and protein analysis were conducted to determine the relative amounts of VGCC subunit expression. α1C, α1D, and α2/δ1 subunits showed an increase of expression after sustained ethanol exposure. However, the β4 subunit showed a decrease. Furthermore, α1A, α1B, and α1F subunits did not alter in their relative expression. Thus, sustained ethanol exposure may participate in the development of ethanol dependence in neurons. [31]
Other experiments done by Malysz et al. have looked into ethanol effects on voltage-gated calcium channels on detrusor smooth muscle cells in guinea pigs. Perforated patch clamp technique was used having intracellular fluid inside the pipette and extracellular fluid in the bath with added 0.3% vol/vol (about 50-mM) ethanol. Ethanol decreased the Ca2+
current in DSM cells and induced muscle relaxation. Ethanol inhibits VGCCs and is involved in alcohol-induced relaxation of the urinary bladder. [32]
Research on the desert grass spider, Agelenopsis aperta, has shown that agatoxins IVA and IVB found in their venom selectively block calcium channels. These agatoxins are found in other spider species as well. Desert grass spider bites to insects result in rapid paralysis, but bites to humans are not considered medically significant. [33]
In the body's tissues, the concentration of calcium ions (Ca2+
) outside cells is normally about 10,000-fold higher than the concentration inside cells. Embedded in the membrane of some cells are calcium channels. When these cells receive a certain signal, the channels open, letting calcium rush into the cell. The resulting increase in intracellular calcium has different effects in different types of cells. Calcium channel blockers prevent or reduce the opening of these channels and thereby reduce these effects.[ citation needed ]
Several types of calcium channels occur, with a number of classes of blockers, but almost all of them preferentially or exclusively block the L-type voltage-gated calcium channel. [34]
Voltage-dependent calcium channels are responsible for excitation-contraction coupling of skeletal, smooth, and cardiac muscle and for regulating aldosterone and cortisol secretion in endocrine cells of the adrenal cortex. [5] In the heart, they are also involved in the conduction of the pacemaker signals. CCBs used as medications primarily have four effects:
Since blood pressure is in intimate feedback with cardiac output and peripheral resistance, with relatively low blood pressure, the afterload on the heart decreases; this decreases how hard the heart must work to eject blood into the aorta, so the amount of oxygen required by the heart decreases accordingly. This can help ameliorate symptoms of ischaemic heart disease such as angina pectoris.
Reducing the force of contraction of the myocardium is known as the negative inotropic effect of calcium channel blockers.
Slowing down the conduction of electrical activity within the heart, by blocking the calcium channel during the plateau phase of the action potential of the heart (see: cardiac action potential), results in a negative chronotropic effect, or a lowering of heart rate. This can increase the potential for heart block. The negative chronotropic effects of CCBs make them a commonly used class of agents in individuals with atrial fibrillation or flutter in whom control of the heart rate is generally a goal. Negative chronotropy can be beneficial when treating a variety of disease processes because lower heart rates represent lower cardiac oxygen requirements. Elevated heart rate can result in significantly higher "cardiac work", which can result in symptoms of angina.
The class of CCBs known as dihydropyridines mainly affect arterial vascular smooth muscle and lower blood pressure by causing vasodilation. The phenylalkylamine class of CCBs mainly affect the cells of the heart and have negative inotropic and negative chronotropic effects. The benzothiazepine class of CCBs combine effects of the other two classes.
Because of the negative inotropic effects, the nondihydropyridine calcium channel blockers should be avoided (or used with caution) in individuals with cardiomyopathy. [35]
Unlike beta blockers, calcium channel blockers do not decrease the responsiveness of the heart to input from the sympathetic nervous system. Since moment-to-moment blood pressure regulation is carried out by the sympathetic nervous system (via the baroreceptor reflex), calcium channel blockers allow blood pressure to be maintained more effectively than do beta blockers. However, because dihydropyridine CCBs result in a decrease in blood pressure, the baroreceptor reflex often initiates a reflexive increase in sympathetic activity leading to increased heart rate and contractility.
Ionic calcium is antagonized by magnesium ions in the nervous system. Because of this, bioavailable supplements of magnesium, possibly including magnesium chloride, magnesium lactate, and magnesium aspartate, may increase or enhance the effects of calcium channel blockade. [36]
N-type calcium channels are found in neurons and are involved in the release of neurotransmitter at synapses. Ziconotide is a selective blocker of these calcium channels and acts as an analgesic. [16]
Calcium channel blockers came into wide use in the 1960s, [37] having been first identified in the lab of German pharmacologist Albrecht Fleckenstein in 1964. [38]
BK channels (big potassium), are large conductance calcium-activated potassium channels, also known as Maxi-K, slo1, or Kca1.1. BK channels are voltage-gated potassium channels that conduct large amounts of potassium ions (K+) across the cell membrane, hence their name, big potassium. These channels can be activated (opened) by either electrical means, or by increasing Ca2+ concentrations in the cell. BK channels help regulate physiological processes, such as circadian behavioral rhythms and neuronal excitability. BK channels are also involved in many processes in the body, as it is a ubiquitous channel. They have a tetrameric structure that is composed of a transmembrane domain, voltage sensing domain, potassium channel domain, and a cytoplasmic C-terminal domain, with many X-ray structures for reference. Their function is to repolarize the membrane potential by allowing for potassium to flow outward, in response to a depolarization or increase in calcium levels.
Verapamil, sold under various trade names, is a calcium channel blocker medication used for the treatment of high blood pressure, angina, and supraventricular tachycardia. It may also be used for the prevention of migraines and cluster headaches. It is given by mouth or by injection into a vein.
Amlodipine, sold under the brand name Norvasc among others, is a calcium channel blocker medication used to treat high blood pressure, coronary artery disease (CAD) and variant angina. It is taken orally.
Nifedipine, sold under the brand name Procardia among others, is a calcium channel blocker medication used to manage angina, high blood pressure, Raynaud's phenomenon, and premature labor. It is one of the treatments of choice for Prinzmetal angina. It may be used to treat severe high blood pressure in pregnancy. Its use in preterm labor may allow more time for steroids to improve the baby's lung function and provide time for transfer of the mother to a well qualified medical facility before delivery. It is a calcium channel blocker of the dihydropyridine type. Nifedipine is taken by mouth and comes in fast- and slow-release formulations.
Diltiazem, sold under the brand name Cardizem among others, is a nondihydropyridine calcium channel blocker medication used to treat high blood pressure, angina, and certain heart arrhythmias. It may also be used in hyperthyroidism if beta blockers cannot be used. It is taken by mouth or given by injection into a vein. When given by injection, effects typically begin within a few minutes and last a few hours.
Voltage-gated calcium channels (VGCCs), also known as voltage-dependent calcium channels (VDCCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (e.g. muscle, glial cells, neurons) with a permeability to the calcium ion Ca2+. These channels are slightly permeable to sodium ions, so they are also called Ca2+–Na+ channels, but their permeability to calcium is about 1000-fold greater than to sodium under normal physiological conditions.
Ryanodine receptors form a class of intracellular calcium channels in various forms of excitable animal tissue like muscles and neurons. There are three major isoforms of the ryanodine receptor, which are found in different tissues and participate in different signaling pathways involving calcium release from intracellular organelles. The RYR2 ryanodine receptor isoform is the major cellular mediator of calcium-induced calcium release (CICR) in animal cells.
Lercanidipine is an antihypertensive drug. It belongs to the dihydropyridine class of calcium channel blockers, which work by relaxing and opening the blood vessels allowing the blood to circulate more freely around the body. This lowers the blood pressure and allows the heart to work more efficiently.
Nitrendipine is a dihydropyridine calcium channel blocker. It is used in the treatment of primary (essential) hypertension to decrease blood pressure and can reduce the cardiotoxicity of cocaine.
Calcium channel, voltage-dependent, L type, alpha 1C subunit is a protein that in humans is encoded by the CACNA1C gene. Cav1.2 is a subunit of L-type voltage-dependent calcium channel.
Calciseptine (CaS) is a natural neurotoxin isolated from the black mamba Dendroaspis p. polylepis venom. This toxin consists of 60 amino acids with four disulfide bonds. Calciseptine specifically blocks L-type calcium channels, but not other voltage-dependent Ca2+ channels such as N-type and T-type channels.
T-type calcium channels are low voltage activated calcium channels that become inactivated during cell membrane hyperpolarization but then open to depolarization. The entry of calcium into various cells has many different physiological responses associated with it. Within cardiac muscle cell and smooth muscle cells voltage-gated calcium channel activation initiates contraction directly by allowing the cytosolic concentration to increase. Not only are T-type calcium channels known to be present within cardiac and smooth muscle, but they also are present in many neuronal cells within the central nervous system. Different experimental studies within the 1970s allowed for the distinction of T-type calcium channels from the already well-known L-type calcium channels. The new T-type channels were much different from the L-type calcium channels due to their ability to be activated by more negative membrane potentials, had small single channel conductance, and also were unresponsive to calcium antagonist drugs that were present. These distinct calcium channels are generally located within the brain, peripheral nervous system, heart, smooth muscle, bone, and endocrine system.
The L-type calcium channel is part of the high-voltage activated family of voltage-dependent calcium channel. "L" stands for long-lasting referring to the length of activation. This channel has four isoforms: Cav1.1, Cav1.2, Cav1.3, and Cav1.4.
Cav1.1 also known as the calcium channel, voltage-dependent, L type, alpha 1S subunit, (CACNA1S), is a protein which in humans is encoded by the CACNA1S gene. It is also known as CACNL1A3 and the dihydropyridine receptor.
Calcium channel, voltage-dependent, L type, alpha 1D subunit is a protein that in humans is encoded by the CACNA1D gene. Cav1.3 channels belong to the Cav1 family, which form L-type calcium currents and are sensitive to selective inhibition by dihydropyridines (DHP).
Efonidipine (INN) is a dihydropyridine calcium channel blocker marketed by Shionogi & Co. of Japan. It was launched in 1995, under the brand name Landel (ランデル). The drug blocks both T-type and L-type calcium channels. Drug Controller General of India (DCGI) has approved the use of efonidipine in India. It is launched under the brand name "Efnocar".
Devapamil is a calcium channel blocker. It is also known as desmethoxyverapamil, which is a phenylalkylamine (PAA) derivative. Devapamil not only inhibits by blocking the calcium gated channels, but also by depolarizing the membrane during the sodium-potassium exchanges.
Anipamil is a calcium channel blocker, specifically of the phenylalkylamine type. This type is separate from its more common cousin Dihydropyridine. Anipamil is an analog of the more common drug verapamil, which is the most common type of phenylalkylamine style calcium channel blocker. Anipamil has been shown to be a more effective antiarrhythmic medication than verapamil because it does not cause hypertension as seen in verapamil. It is able to do this by bonding to the myocardium tighter than verapamil.
AH-1058 is a lipophilic antiarrhythmic calcium channel blocker synthesized by the Pharmaceutical Research Laboratories of Ajinomoto Co., Inc in Kawasaki, Japan. It is derived from cyproheptadine, a compound with known antiserotonic, antihistaminic and calcium channel blocking properties. The IUPAC name of AH-1058 is: 4-(5H-dibenzo[a,d]cyclohepten-5-ylidene)-1-[E-3-(3-methoxy-2-nitro) phenyl-2-propenyl]piperidine hydrochloride.
Dihydropyridine calcium channel blockers are derivatives of 1,4-dihydropyridine that are used as L-type calcium channel blockers. They are used in the treatment of hypertension.