A<unk><unk>  embedded in a cell membrane. In the body's tissues, the concentration of<unk>  ions () outside cells is normally about 10,000-fold higher than the concentration inside cells. Embedded in the membrane of some cells are<unk><unk> s. When these cells receive a certain signal, the<unk> s open, letting<unk>  rush into the cell. The resulting increase in intracellular<unk>  has different effects in different types of cells.<unk> s prevent or reduce the opening of these<unk> s and thereby reduce these effects. Several types of<unk><unk> s occur, with a number of classes of blockers, but almost all of them preferentially or exclusively block the L-type voltage-gated<unk><unk> . Voltage-dependent<unk><unk> s 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. In the heart, they are also involved in the conduction of the pacemaker signals.<unk> s used as medications primarily have four effects: * By acting on vascular smooth muscle, they reduce contraction of the arteries and cause an increase in arterial diameter, a phenomenon called vasodilation <unk> s do not work on venous smooth muscle). * By acting on cardiac muscles (myocardium), they reduce the force of contraction of the heart. * By slowing down the conduction of electrical activity within the heart, they slow down the heart beat. * By blocking the<unk>  signal on adrenal cortex cells, they directly reduce aldosterone production, which correlates to lower blood pressure. 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. Immunohistochemical analysis of L-type<unk><unk>  Cav1.3 (CACNA1D) in human adrenal cortex: Marked immunoreactivity was detected in the zona glomerulosa. In the figure: ZG = zona glomerulosa, ZF = zona fasciculata, AC = adrenal capsule. Immunohistochemistry was performed according to published methods. Reducing the force of contraction of the myocardium is known as the negative inotropic effect of<unk> s. Slowing down the conduction of electrical activity within the heart, by blocking the<unk><unk>  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<unk> s 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<unk> s known as dihydropyridines mainly affect arterial vascular smooth muscle and lower blood pressure by causing vasodilation. The phenylalkylamine class of<unk> s mainly affect the cells of the heart and have negative inotropic and negative chronotropic effects. The benzothiazepine class of<unk> s combine effects of the other two classes. Because of the negative inotropic effects, the nondihydropyridine<unk> s should be avoided (or used with caution) in individuals with cardiomyopathy. Unlike beta blockers,<unk> s 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),<unk> s allow blood pressure to be maintained more effectively than do beta blockers. However, because dihydropyridine<unk> s 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<unk>  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<unk><unk>  blockade. N-type<unk><unk> s are found in neurons and are involved in the release of neurotransmitter at synapses. Ziconotide is a selective blocker of these<unk><unk> s and acts as an analgesic.
Calcium channel blocker
Beta blocker
Channel blocker
ACE inhibitor
Channel opener
Angiotensin II receptor blocker
Beta-adrenergic agonist
Mercurial diuretic