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Myocardial Contractility
Myocardial contractility represents the innate ability of the heart muscle (cardiac muscle or myocardium) to contract. The ability to produce changes in force during contraction result from incremental degrees of binding between different types of tissue, that is, between filaments of myosin (thick) and actin (thin) tissue. The degree of binding depends upon the concentration of calcium ions in the cell. Within an in vivo intact heart, the action/response of the sympathetic nervous system is driven by precisely timed releases of a catecholamine, which is a process that determines the concentration of calcium ions in the cytosol of cardiac muscle cells. The factors causing an increase in contractility work by causing an increase in intracellular calcium ions (Ca++) during contraction. Mechanisms for altering contractility Increasing contractility is done primarily through increasing the influx of calcium or maintaining higher calcium levels in the cytosol of cardiac myocytes during ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cardiac Muscle
Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. The cardiac muscle (myocardium) forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium), with blood supplied via the coronary circulation. It is composed of individual cardiac muscle cells joined by intercalated discs, and encased by collagen fibers and other substances that form the extracellular matrix. Cardiac muscle contracts in a similar manner to skeletal muscle, although with some important differences. Electrical stimulation in the form of a cardiac action potential triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum. The rise in calcium causes the c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphorylation
In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. Protein phosphorylation often activates (or deactivates) many enzymes. Glucose Phosphorylation of sugars is often the first stage in their catabolism. Phosphorylation allows cells to accumulate sugars because the phosphate group prevents the molecules from diffusing back across their transporter. Phosphorylation of glucose is a key reaction in sugar metabolism. The chemical equation for the conversion of D-glucose to D-glucose-6-phosphate in the first step of glycolysis is given by :D-glucose + ATP → D-glucose-6-phosphate + ADP :ΔG° = −16.7 kJ/mol (° indicates measurement at standard condition) Hepatic cells are freely permeable to glucose, an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ATPase
ATPases (, Adenosine 5'-TriPhosphatase, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, SV40 T-antigen, ATP hydrolase, complex V (mitochondrial electron transport), (Ca2+ + Mg2+)-ATPase, HCO3−-ATPase, adenosine triphosphatase) are a class of enzymes that catalyze the decomposition of ATP into ADP and a free phosphate ion or the inverse reaction. This dephosphorylation reaction releases energy, which the enzyme (in most cases) harnesses to drive other chemical reactions that would not otherwise occur. This process is widely used in all known forms of life. Some such enzymes are integral membrane proteins (anchored within biological membranes), and move solutes across the membrane, typically against their concentration gradient. These are called transmembrane ATPases. Functions Transmembrane ATPases import metabolites necessary for cell metabolism and export toxins, wastes, and solutes that can hinder cellular processes. An important example is the sodium-po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bowditch Effect
The Bowditch effect, also known as the Treppe phenomenon and the Treppe effect, is an autoregulation method by which myocardial tension increases with an increase in heart rate. It was first observed by Henry Pickering Bowditch in 1871. Mechanism The underlying cause of the Bowditch effect is an increase in the calcium concentration in the sarcoplasmic reticulum of cardiac muscle cells, and its increased release into sarcoplasm. One of the explanations for an increase in the intracellular calcium concentration is the inability of the Na+/K+-ATPase to keep up with influx of sodium at higher heart rates. When a higher heart rate occurs, for example due to adrenergic stimulation, the L-type calcium channel has increased activity. The sodium-calcium exchanger (which allows 3 Na+ to flow down its electrochemical gradient in exchange for 1 Ca++ ion to flow out of the cell) works to decrease the levels of intracellular calcium. As the heart rate becomes more robust, and the length ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anrep Effect
The Anrep effect is an autoregulation method in which myocardial contractility increases with afterload. It was experimentally determined that increasing afterload caused a proportional linear increase in ventricular inotropy. This effect is found in denervated heart preparations, such as the Starling Preparation, and represents an intrinsic autoregulation mechanism. Physiology Sustained myocardial stretch activates tension-dependent Na+/H+ exchangers, bringing Na+ ions into the sarcolemma. This increase in Na+ in the sarcolemma, reduces the Na+ gradient exploited by sodium-calcium exchanger (NCX), and stops them from working effectively. Ca2+ ions accumulate inside the sarcolemma as a result, and are taken up by sarco(endo)plasmic reticulum Ca2+-ATPase ( SERCA) pumps. Calcium induced calcium release (CICR) from the sarcoplasmic reticulum is thus increased upon the next activation of the cardiac myocyte. This leads to an increase in the force of contraction of the c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inotrope
An inotrope is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction. The term ''inotropic state'' is most commonly used in reference to various drugs that affect the strength of contraction of heart muscle. However, it can also refer to pathological conditions. For example, enlarged heart muscle can increase inotropic state, whereas dead heart muscle can decrease it. Medical uses Both positive and negative inotropes are used in the management of various cardiovascular conditions. The choice of agent depends largely on specific pharmacological effects of individual agents with respect to the condition. One of the most important factors affecting inotropic state is the level of calcium in the cytoplasm of the muscle cell. Positive inotropes usually increase this level, while negative inotropes decrease it. However, not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Afterload
Afterload is the pressure that the heart must work against to eject blood during systole (ventricular contraction). Afterload is proportional to the average arterial pressure. As aortic and pulmonary pressures increase, the afterload increases on the left and right ventricles respectively. Afterload changes to adapt to the continually changing demands on an animal's cardiovascular system. Afterload is proportional to mean systolic blood pressure and is measured in millimeters of mercury (mm Hg). Hemodynamics Afterload is a determinant of cardiac output. Cardiac output is the product of stroke volume and heart rate. Afterload is a determinant of stroke volume (in addition to preload, and strength of myocardial contraction). Following Laplace's law, the tension upon the muscle fibers in the heart wall is the pressure within the ventricle multiplied by the volume within the ventricle divided by the wall thickness (this ratio is the other factor in setting the afterload). T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
L-type Calcium Channels
The L-type calcium channel (also known as the dihydropyridine channel, or DHP 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. L-type calcium channels are responsible for the excitation-contraction coupling of skeletal, smooth, cardiac muscle, and for aldosterone secretion in endocrine cells of the adrenal cortex. They are also found in neurons, and with the help of L-type calcium channels in endocrine cells, they regulate neurohormones and neurotransmitters. They have also been seen to play a role in gene expression, mRNA stability, neuronal survival, ischemic-induced axonal injury, synaptic efficacy, and both activation and deactivation of other ion channels. In cardiac myocytes, the L-type calcium channel passes inward Ca2+ current (ICaL) and triggers calcium release from the sarcoplasmic reticulum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Troponin C
Troponin C is a protein which is part of the troponin complex. It contains four calcium-binding EF hands, although different isoforms may have fewer than four functional calcium-binding subdomains. It is a component of thin filaments, along with actin and tropomyosin. It contains an N lobe and a C lobe. The C lobe serves a structural purpose and binds to the N domain of troponin I (TnI). The C lobe can bind either Ca2+ or Mg2+. The N lobe, which binds only Ca2+, is the regulatory lobe and binds to the C domain of troponin I after calcium binding. Isoforms The tissue specific subtypes are: * Slow troponin C, TNNC1 (3p21.1 ) * Fast troponin C, TNNC2 (20q12-q13.11, ) Mutations Point mutations can occur in troponin C inducing alterations to Ca2+ and Mg2+ binding and protein structure, leading to abnormalities in muscle contraction. In cardiac muscle, they are related to dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM). These known point mutations ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lusitropy
Lusitropy is the rate of myocardial relaxation. The increase in cytosolic calcium of cardiomyocytes via increased uptake leads to increased myocardial contractility (positive inotropic effect), but the myocardial relaxation, or lusitropy, decreases. This should not be confused, however, with catecholamine-induced calcium uptake into the sarcoplasmic reticulum, which increases lusitropy. __TOC__ Positive Increased catecholamine levels promote positive lusitropy, enabling the heart to relax more rapidly. This effect is mediated by the phosphorylation of phospholamban Phospholamban, also known as PLN or PLB, is a micropeptide protein that in humans is encoded by the ''PLN'' gene. Phospholamban is a 52-amino acid integral membrane protein that regulates the calcium (Ca2+) pump in cardiac muscle cells. Func ... and troponin I via a cAMP-dependent pathway. Catecholamine-induced calcium influx into the sarcoplasmic reticulum increases both inotropy and lusitropy. In other wor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sarcoplasmic Reticulum
The sarcoplasmic reticulum (SR) is a membrane-bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca2+). Calcium ion levels are kept relatively constant, with the concentration of calcium ions within a cell being 10,000 times smaller than the concentration of calcium ions outside the cell. This means that small increases in calcium ions within the cell are easily detected and can bring about important cellular changes (the calcium is said to be a second messenger). Calcium is used to make calcium carbonate (found in chalk) and calcium phosphate, two compounds that the body uses to make teeth and bones. This means that too much calcium within the cells can lead to hardening (calcification) of certain intracellular structures, including the mitochondria, leading to cell death. Therefore, it is vital that calcium ion levels are controlled tightly, and can be released in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
