Cardiac muscle regulation

Metzger, J. M., and M. V. Westfall. 2004. Covalent and noncovalent modification of thin filament action. The essential role of troponins in cardiac muscle regulation. Circulation Research 94 146-158. 

The Ca2+-binding subunit TN-C is homologous to calmodulin with four EF-hands. In contrast to calmodulin, which is ubiquitously expressed in multicellular eukaryotic organisms and interacts with many targets, troponin specifically regulates muscle contraction. There are some structural differences between Troponin C in skeletal and cardiac muscles reflecting their physiological differences. 

NFAT2 plays a key role in the development of the embryo s heart. In the precursor cells, there is a temporal and spatial specific expression of NFAT2, which directs the formation of the valves and the septum in the heart. In the adult heart, NFAT proteins also cooperate with transcription factors of the GATA and MEF2 families to regulate cardiac muscle hypertrophic responses. 

The contraction of muscles from all sources occurs by the general mechanism described above. Muscles from different organisms and from different cells and tissues within the same organism may have different molecular mechanisms responsible for the regulation of their contraction and relaxation. In all systems, plays a key regulatory role. There are two general mechanisms of regulation of muscle contraction actin-based and myosin-based. The former operates in skeletal and cardiac muscle, the latter in smooth muscle. 

Actin-based regulation of muscle occurs in vertebrate skeletal and cardiac muscles, both striated. In the gen-... 

As stated above, extracellular Ca plays an important role in contraction of cardiac muscle but not in skeletal muscle. This means that Ca both enters and leaves myocytes in a regulated manner. We shall briefly consider three transmembrane proteins that play roles in this process. 

Troponins T or I Proteins found predominantly in cardiac muscle that regulate calcium-mediated interaction of actin and myosin troponins I and T are released into the blood from myocytes at the time of myocardial cell necrosis after infarction. These biochemical markers become elevated and are used in the diagnosis of myocardial infarction. 

The hypothalamus plays a particularly important role in regulating the autonomic nervous system, which innervates cardiac muscle, smooth muscle, and glands. Many of these effects involve ascending or descending... 

The autonomic nervous system (ANS), also known as the visceral or involuntary nervous system, functions below the level of consciousness. Because it innervates cardiac muscle, smooth muscle, and various endocrine and exocrine glands, this nervous system influences the activity of most of the organ systems in the body. Therefore, it is evident that the ANS makes an important contribution to the maintenance of homeostasis. Regulation of blood pressure gastrointestinal responses to food contraction of the urinary bladder focusing of the eyes and thermoregulation are just a few of the many... 

In smooth muscle, the sarcoplasmic reticulum (SR) plays an important role in regulating cell excitability by communicating intimately with ion channels in the surface membrane. In most cases, Ca2+ release from ryanodine-sensitive Ca2+ release channels (RyRs) in the SR leads to a paradoxical decrease in smooth muscle cell excitability due to activation of plasma membrane K+ channels (Fig. 1 Nelson et al 1995). This is in stark contrast to cardiac muscle, where Ca2+ release from RyRs supplies the majority (> 90%) of Ca2+ required for contraction (Cheng et al 1993, Cannell et al 1995). In this paper, we will briefly review the basic... 

Major effector proteins for G-pro-tein-coupled receptors include adenylate cyclase (ATP intracellular messenger cAMP), phospholipase C (phos-phatidylinositol intracellular messengers inositol trisphosphate and di-acylglycerol), as well as ion channel proteins. Numerous cell functions are regulated by cellular cAMP concentration, because cAMP enhances activity of protein kinase A, which catalyzes the transfer of phosphate groups onto functional proteins. Elevation of cAMP levels inter alia leads to relaxation of smooth muscle tonus and enhanced contractility of cardiac muscle, as well as increased glycogenolysis and lipolysis (p. 

Zaloga, G. P., Roberts, P. R., and Nelson, T. E. (1996). Carnosine A novel peptide regulator of intreacellular calcium and contractility in cardiac muscle. New Horiz. 4, 26-35. 

Ca normally circulates in the bloodstream, within a 2.25-2.50 mmol concentration range, bound to proteins (40 5%), complexed with ions (8-10%), and ionized as Ca " " (45-50%) (Weaver and Heaney, 2006a). Circulating Ca in excess of that required for maintenance of plasma levels is ideally transferred from the blood to be deposited in bone via the bone formation process. The Ca concentration outside of blood vessels in the ECF that bathes cells is tightly regulated close to 1.25 mmol (Weaver and Heaney, 2006a), almost to the point of invariance. It is this ECF Ca pool that cells are immediately reliant upon to sustain vital cellular functions that are imminently critical to the maintenance of life (e.g., cardiac muscle contraction). Circulating Ca is constantly utilized to replenish ECF pools, and when Ca derived from dietary intake is insufficient to replace the amoimt of Ca used for replenishment, Ca in bone is transferred to the blood via a bone resorption process. 

Autonomic receptors further regulate calcium influx through the sarcolemma (Fig. 15.1). (3-Adrenergic stimulation results in the association of a catalytic subunit of a G protein coupled to the (3-receptor. This stimulates the enzyme adenylyl cyclase to convert ATP to cyclic adenosine monophosphate (cAMP). Increasing cAMP production results in a cAMP-dependent phosphorylation of the L-type calcium channel and a subsequent increase in the probability of the open state of the channel. This translates to an increase in transsarcolemmal calcium influx during phase 2 (the plateau phase) of the cardiac muscle action potential. The effects of transient increases in intracellular levels of cAMP are tightly con-... 

Shibata Y, Miyahara A, Okayama T, Kuraoka A, Iida H Gap junction formation and regulation in cultured adult rat and guinea pig cardiac muscle cells in Kanno Y, Kataoka K, Shiba Y, Shibata Y Shimazu T (eds) Intercellular Communication through Gap Junctions. Progress in Cell Research, vol 4. Amsterdam, Elsevier, 1995, pp 151-154. 

The principle of thermal recycling is also used in reactors with a boiling layer, in which the heat from the hot region of the reactor is transported to the cold region by circulating solid particles suspended in the gas flow.15 Methods of the theory of chemical reactor regulation have been successfully used in other sciences as well. We note the model of Belousov-Zhabotinskii, proposed for the description of heart disease, of spasmatic contractions of the cardiac muscle. 

Mechanisms that then restore the basal cytosolic [Ca2+] levels remain unclear. Besides a Ca2+-ATPase on the osteoclast dorsal surface relatively little is known of alternative or parallel methods for Ca2+ extrusion (Zaidi et al., 1993) although there is recent functional, evidence for a Na+/Ca2+ exchanger that, in analogy to the regulation of cytoplasmic [Ca2+] in cardiac muscle could be linked to the proton extrusion that is a primary determinant of the rate and extent of bone resorption (Moonga et al., 2001). 

Target tissues are smooth muscle, cardiac muscle, and glands Cell bodies are absent in cervical, lower lumbar, and coccygeal levels of the spinal cord The neurons have involuntary regulation only... 

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