Myocardial membranes

In contrast to numerous literature data, which indicate that protein oxidation, as a rule, precedes lipid peroxidation, Parinandi et al. [66] found that the modification of proteins in rat myocardial membranes exposed to prooxidants (ferrous ion/ascorbate, cupric ion/tert-butyl-hydroperoxide, linoleic acid hydroperoxide, and soybean lipoxygenase) accompanied lipid peroxidation initiated by these prooxidant systems. 

Pharmacology Propafenone is a Class 1C antiarrhythmic with local anesthetic effects and direct stabilizing action on myocardial membranes. 

Studies of sudden death in novice as well as experienced drug abusers found that cocaine causes vasoconstriction of the coronary arteries which seems to result from an enhancement of Ca2+ influx across myocardial membranes. However, remember that this class of drug affects other neurotransmitter systems. Cocaine inhbiits reuptake of NE and 5-HT as well as binds to the DA transporter. It increases catecholamine receptor sensitivity but does not seem to directly influence enkephalinergic receptors. In addition it also affects neurotransmission the H, Ach and phenylethylamine pathways. Activation of DA, NE or 5-HT neurons independently does not produce the euphoria associated with cocaine misuse. Euphoria seems to be related to simultaneous inteeraction between catecholamine and serotoninergic systems. 

A variety of other calcium transport systems are associated with Ca21-activated ATPases. The extraembryonic structure, the chorioallantoic membrane, of the chick embryo is responsible for the translocation of over 120 mg of eggshell calcium into (he embryo during development. The enzyme responsible for this is a (Ca2+, Mg2+)-ATPase with Km values for Ca2+ of 30 p,mol dm-3 and 0.3 mmol dm-3, and a molecular weight of 170 000. The enzyme can be crossiinked and co-isolated with a calcium-binding protein.158 Transport of Ca2+ is also associated with (Ca2+, Mg2+)-ATPases in neutrophil plasma membranes,159 transverse tubule membranes from rabbit skeletal muscle,160 rabbit myocardial membrane,161 endoplasmic reticulum,162 sar-colemma,163 brain microsomes,164 the Golgi apparatus165 and rat liver plasma membranes.166... 

The mode of action of antiarrhythmics is related to their non-specific interaction with myocardial membranes and it is thought that antiarrhythmics stabilize the... 

Moricizine (600 to 900 mg/day given every 8 hours in three equally divided doses) is indicated in the treatment of documented ventricular arrhythmias, such as sustained ventricular tachycardia, that are life threatening. Because of the proarrhythmic effects of moricizine, its use should be reserved for patients in whom the benefits of treatment outweigh the risks. Moricizine is a class 1C antiarrhythmic agent with potent local anesthetic activity and myocardial-membrane-stabilizing effects. It shares some of the characteristics of the class lA (disopyramide, procainamide, or quinidine), of class IB (lidocaine, mexiletene, phenytoin, or tocainide), or class 1C agents (encainide, flecainide, or propafenone) in that it reduces the fast inward current carried by sodium ions. Moricizine shortens phase 2 and 3... 

Propafenone is a class 1C antiarrhythmic drug with local anesthetic effects and a direct stabilizing action on myocardial membranes. The electrophysiological effect of propafenone manifests itself in a reduction of upstroke velocity (phase O) of the monophasic action potential. In Purkinje fibers, and to a lesser extent myocardial fibers, propafenone reduces the fast inward current carried by sodium ions. The diastolic excitability threshold is increased, and the effective refractory period prolonged. Propafenone reduces spontaneous automaticity and depresses triggered activity. 

Although blood pressure control follows Ohm s law and seems to be simple, it underlies a complex circuit of interrelated systems. Hence, numerous physiologic systems that have pleiotropic effects and interact in complex fashion have been found to modulate blood pressure. Because of their number and complexity it is beyond the scope of the current account to cover all mechanisms and feedback circuits involved in blood pressure control. Rather, an overview of the clinically most relevant ones is presented. These systems include the heart, the blood vessels, the extracellular volume, the kidneys, the nervous system, a variety of humoral factors, and molecular events at the cellular level. They are intertwined to maintain adequate tissue perfusion and nutrition. Normal blood pressure control can be related to cardiac output and the total peripheral resistance. The stroke volume and the heart rate determine cardiac output. Each cycle of cardiac contraction propels a bolus of about 70 ml blood into the systemic arterial system. As one example of the interaction of these multiple systems, the stroke volume is dependent in part on intravascular volume regulated by the kidneys as well as on myocardial contractility. The latter is, in turn, a complex function involving sympathetic and parasympathetic control of heart rate intrinsic activity of the cardiac conduction system complex membrane transport and cellular events requiring influx of calcium, which lead to myocardial fibre shortening and relaxation and affects the humoral substances (e.g., catecholamines) in stimulation heart rate and myocardial fibre tension. 

MI Myocardial ischaemia MIF Migration inhibition factor mIL Mouse interleukin MI/R Myocardial ischaemia/ reperfiision MIRL Membrane inhibitor of reactive lysis... 

Another vasoactive substance produced by the endothelium is thromboxane A2 (TxA2). Normally, small amounts of TxA2 are released continuously however, increased synthesis appears to be associated with some cardiac diseases. Synthesized from arachidonic acid, a plasma membrane phospholipid, TxA2 is a potent vasoconstrictor. Furthermore, this substance stimulates platelet aggregation, suggesting that it plays a role in thrombotic events such as myocardial infarction (heart attack). Nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen block formation of TxA2 and reduce formation of blood clots. 

Phospholamban (PLB or PLN) is a single-pass, 52-residue integral membrane protein that regulates myocardial contractility by direct physical interaction with sarco(endo)plasmic reticulum Ca-ATPase (SERCA), a 110-kDa enzyme that maintains calcium homeostasis in the sarcoplasmic... 

Myocardial tissue pH measurement has been used in the studies of different approaches to myocardial protection in various cardiac operations. A needle type glass membrane miniature electrode has been used in studies for pH-guided myocardial management [127], As described in the previous section, this electrode was also adapted to measure brain pH [132], The electrode has a right-angled glass electrode... 

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