Cardiac muscles Isolated

Haimoto H, Kato K. 1988. SlOOaO (alpha alpha) protein in cardiac muscle. Isolation from human cardiac muscle and ultrastructural localization. Eur J Biochem 171(l-2) 409-415. 

The general picture of muscle contraction in the heart resembles that of skeletal muscle. Cardiac muscle, like skeletal muscle, is striated and uses the actin-myosin-tropomyosin-troponin system described above. Unlike skeletal muscle, cardiac muscle exhibits intrinsic rhyth-micity, and individual myocytes communicate with each other because of its syncytial nature. The T tubular system is more developed in cardiac muscle, whereas the sarcoplasmic reticulum is less extensive and consequently the intracellular supply of Ca for contraction is less. Cardiac muscle thus relies on extracellular Ca for contraction if isolated cardiac muscle is deprived of Ca, it ceases to beat within approximately 1 minute, whereas skeletal muscle can continue to contract without an extraceUular source of Ca +. Cyclic AMP plays a more prominent role in cardiac than in skeletal muscle. It modulates intracellular levels of Ca through the activation of protein kinases these enzymes phosphorylate various transport proteins in the sarcolemma and sarcoplasmic reticulum and also in the troponin-tropomyosin regulatory complex, affecting intracellular levels of Ca or responses to it. There is a rough correlation between the phosphorylation of Tpl and the increased contraction of cardiac muscle induced by catecholamines. This may account for the inotropic effects (increased contractility) of P-adrenergic compounds on the heart. Some differences among skeletal, cardiac, and smooth muscle are summarized in... 

To certify the important role of Ca in the excitatory action of MTX, the effect of MTX on the Ca movements in cardiac muscle was examined at the cellular level. Figure 8 shows the time course of the Ca influx in the presence or absence of MTX (10 g/mL). The Ca uptake in the control experiment increased with time, to reach a saturation level about 5 min after administration of Ca. When MTX (10 g/mL) and Ca were applied simultaneously, the increase in Ca uptake at 5 min was 31% larger than that of the control. Furthermore, when the intracellular Ca concentration of isolated cardiac myocytes was determined from the Quin 2 fluorescence, MTX (10 g/mL) caused a marked increase in the free Ca concentration from 122 9 nM (control) to 380 23 nM, as shown in Figure 9. 

The electrophysiological experiments reported here and done with patch-clamp techniques support this idea. The external application of MTX to isolated cardiac myocytes caused a sustained inward current which was carried by Ca . MTX did not increase the voltage-dependent Ca channel current, and both the time dependence and voltage dependence of the MTX-induced current were clearly different from those of the usual Ca channel current. These results suggest that the MTX-induced steady current is different from the usual voltage-dependent Ca channel current, and that this is possibly a current which flows through a new type of Ca -permeable channel. Tbe steady current described here may be responsible for the highly enhanced Ca influx induced by MTX and could account for the excitatory action of MTX on smooth and cardiac muscles. 

Purkinje fibers Papillary muscle Isolated cardiac myocytes... 

Hajo-Tello N, Dupont C, Wepierre J, Cohen Y, Miller R, Godfraind T. (1985). Effects of tabernanthine on calcium and catecholamine stimulated contractions of isolated vascular and cardiac muscle. Arch Int Pharmacodyn Then 276(1) 35-43. 

Direct effects on the heart are determined largely by Bi receptors, although B2 and to a lesser extent a receptors are also involved, especially in heart failure. Beta-receptor activation results in increased calcium influx in cardiac cells. This has both electrical and mechanical consequences. Pacemaker activity—both normal (sinoatrial node) and abnormal (eg, Purkinje fibers)—is increased (positive chronotropic effect). Conduction velocity in the atrioventricular node is increased (positive dromotropic effect), and the refractory period is decreased. Intrinsic contractility is increased (positive inotropic effect), and relaxation is accelerated. As a result, the twitch response of isolated cardiac muscle is increased in tension but abbreviated in duration. In the intact heart, intraventricular pressure rises and falls more rapidly, and ejection time is decreased. These direct effects are easily demonstrated in the absence of reflexes evoked by changes in blood pressure, eg, in isolated myocardial preparations and in patients with ganglionic blockade. In the presence of normal reflex activity, the direct effects on heart rate may be dominated by a reflex response to blood pressure changes. Physiologic stimulation of the heart by catecholamines tends to increase coronary blood flow. 

Herasymowych, O.S. Mani, R.S. Kay, C.M. Isolation, purification and characterization of creatine kinase from bovine cardiac muscle. Biochim. Biophys. Acta, 534, 38-47 (1978)... 

Kanemitsu, E Mizushima, J. Kageoka, T. Okigaki, T. Taketa, K. Kira, S. Characterization of two types of mitochondrial creatine kinase isolated from normal human cardiac muscle and brain tissue. Electrophoresis, 21, 266-270 (2000)... 

The positive benefits of extracts of two species of Digitalis purpurea (foxglove and lanata) were recognized long before the active constituents were isolated and structurally characterized. The cardiac glycosides, which include digoxin, digitoxin, and deslanoside, exert a powerful and selective positive inotropic action on the cardiac muscle (see Chapter 35). 

Enables pretreated cardiac cells to become more resistant to the damage caused by hypoxia-reoxygenation and oxidative stress, enables isolated hearts reperfused in its presence (10 pM) after an ischemic event to display a significant recovery in myocardial performance and to produce a marked and significant reduction in cardiac muscle damage and infarct size [142]... 

Other Tissues. Sulphonylurea receptors have also been described for cardiac muscle, skeletal muscle and smooth muscle but do not appear to be of therapeutic benefit for lowering blood sugar (Panten et al., 1992). Specific binding to membranes isolated from other rat tissues (liver, lung, kidney, heart, spleen, diaphragm, duodenum, colon and stomach) was... 

Parratt JR, Marshall RJ (1974) The response of isolated cardiac muscle to acute anoxia protective effect of adenosine triphosphate and creatine phosphate. J Pharm Pharmacol 26 427-133... 

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