Cardiac Purkinje fibers

Cardiac Action Potential In Vitro Purkinje Fibers. Intracellular recording of action potentials from cardiac Purkinje fibers isolated from dog or sheep ventricle. Measurement of maximum rate of depolarization and action potential duration to detect sodium and potassium channel interactions, respectively, according to recommendations in EM A CPMP Points to Consider document, CPMP 986/96 (1998). 

Reber WR, Weingart R Ungulate cardiac Purkinje fibers The influence of intracellular pH on the elctrical cell-to-cell coupling. J Physiol (Lond) 1982 328 87-104. 

The action potential recorded from a cardiac Purkinje fiber is shown in Figure 23-1. At rest, the interior of the cell is negative relative to the cell s exterior. As in other excitable tissues (neurons, skeletal muscle), an action potential occurs when the cell interior suddenly becomes positive (depolarizes), primarily because of sodium ion influx. The cell interior then returns to a negative potential (repolarizes), primarily because of... 

Fig. 9.6 Top intracellular sodium activity and tension recorded in a cardiac Purkinje fiber during rest and during a period of repetitive stimulation at 2 Hz [28]. Middle reconstruction using a model ventricular cell showing intracellular sodium and calcium...

All beta-blockers cause an increase in atrioventricular conduction time this is most pronounced with drugs that have potent membrane-depressant properties and no partial agonist activity. Sotalol differs from other beta-blockers in that it increases the duration of the action potential in the cardiac Purkinje fibers and ventricular muscle at therapeutic doses. This is a class III antidysr-hythmic effect, and because of this, sotalol has been used to treat ventricular (54-56) and supraventricular dysrhythmias (57). The main serious adverse effect of sotalol is that it is prodysrhythmic in certain circumstances, and can cause torsade de pointes (58,59). 

Weld FW and Bigger JT (1980) Electrophysiological effects of imipramine on ovine cardiac purkinje fibers and ventricular muscle fibers. Circulation Research 46 167-175. 

The electropharmacological effects of berberine on canine cardiac Purkinje fibers and ventricular muscle and atrial muscle, as well as rabbit atrial muscle were studied via conventional microelectrode techniques to obtain intracellular recordings of transmembrane electrical potentials. The results suggest that berberine exerts Class III antiarrhythmic and proarrhythmic actions in canine cardiac muscle in vitro [218]. 

Standard microelectrode techniques were used to study the effects of isocorydine on potential characteristics of canine cardiac Purkinje fibers and ventricular myocardium in vitro. In the Purkinje fibers, the action potential durations APDjj and APD were prolonged at 3 pmol/1 but shortened at 30 pmol/1 by isocorydine. The action potential amplitude and maximal upstroke velocity were decreased at 100 pmol/1. In the ventricular myocardium, the action potential characteristics were changed by isocorydine at concentrations above 30 pmol/1. The APDJ0 was shortened, the APD90 was prolonged, and the maximal upstroke velocity was decreased at 30 pmol/1. The effective refractory period was prolonged by the alkaloid in Purkinje fibers and ventricular myocardium. These results indicated that the alkaloid may interfere with K+, Na+, and Ca+2 currents in myocardial cell membranes at different concentrations [287]. 

Purkinje Fiber The rabbit cardiac purkinje fiber AP assay was recommended as... 

VI. Vaughn-Jones, R. D., Intracellular chloride activity of quiescent cardiac purkinje fibers. 

Gonzalez MD, Vassalle M. 1990. Strontium induces oscillatory potentials in sheep cardiac Purkinje fibers. Int J Cardiol 27 87-99. 

Several substituted benzenesulfonates have been reported to possess pharmacological properties. Doxium (2,5-dihydroxybenzenesulfonate or dobesylate, 38, R = 2-OH, R = 5-OH), is a vasotropic agent, that increased the contractile force in normally working and tetrodoxin-arrested preparations of dog cardiac Purkinje fibers and the adjacent ventricular tissue166,167. 

Varghese, A. R.L. Winslow. 1994. Dynamics of abnormal pacemaking activity in cardiac Purkinje fibers. J. Theor. Biol. 168 407-20... 

Encainide (+) = (-) Action potential parameters of cardiac Purkinje fibers (dog) 80... 

Turgeon, J. Funck-Brentano, C. Gray, H.T. Pavlou, H.N. Prakash, C. Blair, I.A. Roden, D.M. Genetically determined stereoselective excretion of encainide in humans and electrophysiologic effects of its enantiomers in eanine cardiac Purkinje fibers. Clin. Pharmacol. Ther. 1991, 49, 488-496. 

It has been shown that a concentration of 1 mmol/1 cesium in Tyrode solution as the outer medium of cardiac Purkinje fibers — part of the excitable system of the heart — is sufficient to suppress the potassium outward current (pacemaker current) nearly completely . When the concentration of cesium exceeds 20 mmol/1 all detectable potassium currents in cardiac Purkinje fibers are blocked. Since this effect occurred within one or two minutes it was believed that cesium ions are able to block the potassium channels in the membrane from the outside. One possible explanation would be based upon the fact that cesium ions are bigger than potassium ions (diameter [Cs] = 1.77 A [K]" = 1.33 A). Therefore, if they eventually invade the potassium channels, they should be hampered in their motion or even immobilized because of their bigger size. If this was the case, cesium ions would invade potassium channels whenever they reach cell membranes and would irreversibly block them. Besides, cesium ions should not be detectable inside the cells of the excitable system, since they are imable to penetrate the cell membranes. 

Kaseda S, Gihnour RF Jr, Zipes DP (1989). Depressant effect of magnesium on early after depolarizations and triggered activity induced by cesium, quinidine, and 4-aminopyridine in canine cardiac Purkinje fibers. Am Heart J 118 458 66. 

Pallante BA, Giovannone S, Fang-Yu L, Zhang J, Liu N, Kang G, Dun W, Boyden PA, Fishman GI (2010). Contactin-2 expression in the cardiac Purkinje fiber network. Circ Arrhythm Electmphysiol 3(2) 186-194. 

Rozanski GJ, Witt RC (1991). Early after depolarizations and triggered activity in rabbit cardiac Purkinje fibers recovering from ischemic-hke conditions. Role of acidosis. Circulation 83 1352-1360. 

Coraboeuf E, Carmeleit E (1982) Existence of two transient outward currents in sheep cardiac Purkinje fibers. Pflugers Arch 392 352-359... 

Such a model is used here. Consider the cylindrical fiber shown in Figure 19.5, having radius a =75 fj,m and a length of 10 /xm. The fiber is surrounded by an extracellular volume extending 3a beyond the membrane. To establish a symmetric reference potential, the outside edge of the extracellular region was connected via resistances to a junction where e = 0. Intracellular specific resistance Ri was 250 cm, and Rs was one-third of Ri. Solutions for intracellular, extracellular, and transmembrane potentials were obtained through a process of mrmerical simulation. The structure of this example follows that of Spach et al. [1973], where cardiac Purkinje fibers were studied. Most of the examples below use the DiFrancesco-Noble model for Purkinje membrane [Noble et al., 1994]. 

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