Figure 4. Prevention and termination of arrhythmias by EPA. Perfusion of
myocytes with medium containing 7 mM Ca2+ (A,a) or 0.1 mM ouabain (B,a)
induced contracture and fibrillation of myocytes. Washing cells with medium
containing 1.2 mM Ca2+ returned fibrillations to control beating rate (not
shown). Myocytes were then perfused with 7
µM EPA. When beating rate
had slowed addition of 7 mM Ca2+ failed to induce arrhyhthmias (A,b) or 0.1
mM oubain (B,b). C. Fibrillation was induced by ouabain (0.1 mM) plus Ca2+
(5 mM ) in perfusion medium. Addition of EPA (8
µM) terminated
fibrillation. Subsequent addition of delipidated BSA (2 mg/ml) still in the
presence of ouabain and high Ca2+ concentrations, extracted free EPA and the
fibrillation resumed. |
Fig. 4. shows the effects of elevated perfusate
Ca2+ and ouabain on the myoctes. Both agents induced rapid contractions,
contractures and fibrillation of the myocytes. When EPA was added to the
superfusate, the beating rate slowed and when the high Ca2+ or ouabain was
added in the presence of the EPA, no arrhythmia was induced. Furthermore, as
shown in Fig. 4C, after a violent fibrillation was induced in the cells by
both elevated calcium and ouabain, addition of EPA stopped the arrhythmias
and the cells resumed their fairly regular contractions. Then addition of
the delipidated bovine serum albumin to remove the free fatty acid from the
myocytes resulted in the recurrence of the arrhythmia. This taught us two
important facts. First, that the EPA could be extracted from the cells in
the continued presence of the toxins and the arrhythmia returned, indicated
that the fatty acids were acting without strong ionic or covalent binding to
any constituent in the cell membrane. If they had, we would not have been
able to extract the EPA from the cells with the albumin. It seems the free
fatty acids act directly on the heart cells and need only partition
(dissolve) into the hospitable hydrophobic interior of phospholipids of the
plasma membranes of myocytes to elicit their antiarrhythmic actions. Second,
when we tested the ethyl ester of the EPA, it had no prompt antiarrhythmic
action; only the free fatty acid with its negative carboxyl charge is
antiarrhythmic. |
