Influence of the phospholipid content in docosahexaenoic acid on electrophysiology and contraction of rat heart muscle cells.

The cardiovascular beneficial effects of fish oils are currently attributed to docosahexaenoic (C22:6 n-3) and eicosapentaenoic (C20:5 n-3) acids, although most investigations have focused on eicosapentaenoic acid. This study was devoted to the specific effect of docosahexaenoic acid, as compared to eicosapentaenoic acid, on the basal electrophysiological and mechanical characteristics of cultured rat myocardial cells. The myocyte cultures were prepared from newborn rat heart ventricles. The cells were grown for 24 hours in a conventional seric medium, and then incubated in a medium enriched with either docosahexaenoic acid or eicosapentaenoic acid for 96 hours. This treatment resulted in docosahexaenoic acid-rich cells (16% of the phospholipid fatty acids) and docosahexaenoic acid-poor cells (1.5%), both displaying the same phospholipid n-6/n-3 polyunsaturated fatty acid ratio. The transmembrane potentials were recorded with glass microelectrodes. Contractions were monitored photometrically. The action potential amplitude was slightly smaller in docosahexaenoic acid-rich cells (-4 mv), due to a lower plateau phase. There was no difference in action potential duration and spontaneous rate. The contraction measurements were not significantly different between the two groups of cells. We conclude that increasing the docosahexaenoic acid content in cardiomyocyte membrane phospholipids may have modulated the calcium ionic channels governing the plateau phase of the action potential, whereas the other physiological activities remained unaffected.