acetylstrophanthidin and bufogenin

To detect delayed after depolarizations (DAD) in extracellular electrograms using signal averaging technique.. DAD were induced by acetylstrophanthidin (0.25 mumol.L-1, n = 9) and resibufogenin (0.52 mumol.L-1, n = 5) in sheep cardiac Purkinje fibers. Intracellular voltage was recorded with a conventional microelectrode, and simultaneous extracellular electrograms were recorded differentially from widely spaced electrodes placed in the tissue bath. Noise of electrograms was reduced using signal averaging technique.. Acetylstrophanthidin and resibufogenin both induced DAD in the intracellular recording and extracellular DAD (DAD-E) in the extracellular electrogram in sheep heart Purkinje fibers. Acetylstrophanthidin and resibufogenin induced typical changes in the action potential including decrease in action potential amplitude, resting potential, maximum diastolic potential, and action potential duration. Similar shortening occurred in the "Q-T interval" recorded by the extracellular electrogram. With either acetylstrophanthidin or resibufogenin, shortening of stimulation cycle length from 990 ms to 690 ms reduced the coupling interval between action potential upstroke and peak voltage of the DAD (P < 0.01), and the coupling interval between the "QRS" and DAD-E recorded extracellularly (P < 0.01).. DAD can be detected using the extracellular electrograms combined with the high resolution, signal averaging technique.

Topics: Action Potentials; Animals; Arrhythmias, Cardiac; Bufanolides; Cardiotonic Agents; Electrophysiology; In Vitro Techniques; Purkinje Fibers; Sheep; Signal Processing, Computer-Assisted; Strophanthidin

The purpose of this study was to compare the electrotoxicological effects of resibufogenin (RBG) (n = 14) with acetylstrophanthidin (AS) (n = 14) to induce delayed afterdepolarization (DAD) and triggered activity (TA), and their alteration of the electrophysiological properties in sheep cardiac Purkinje fibers using the extracellular electrograms, signal averaging, and standard microelectrode techniques simultaneously. The results indicated: 1) Lower toxic dose of RBG (0.52 mumol.L-1) and AS (0.25 mumol.L-1) induced intracellular and extracellular DAD (DAD-I and DAD-E) at pacing cycle length of 990 and 690 ms. 2) Higher toxic dose of RBG (2.6 mumol.L-1) and AS (5.0 mumol.L-1) induced DAD and TA, nonsustained or sustained premature action potential and oscillatory potentials; 3) At the beginning period of superfusing the drugs, both RBG and AS caused changes of the electrophysiological characteristics. This study demonstrates that the electro-toxicological characteristics and electrophysiological properties of RBG are similar to that of AS and suggests that RBG belongs to the family of digitalis-like drugs.

Topics: Action Potentials; Animals; Arrhythmias, Cardiac; Bufanolides; Cardiotonic Agents; Electrophysiology; In Vitro Techniques; Membrane Potentials; Purkinje Fibers; Sheep; Strophanthidin