Modification of the n-6/n-3 fatty acid ratio in the phospholipids of rat ventricular myocytes in culture by the use of synthetic media: functional and biochemical consequences in normoxic and hypoxic conditions.

The respective roles of exogenous polyunsaturated fatty acids on the lipid composition, physiological properties and enzyme release was investigated on isolated cardiac muscle cells in normoxia and hypoxia. Rat neonatal ventricular myocytes were grown for 5 days in conventional serum-supplemented medium. Cells were then incubated for 24 h in fully chemically-defined media featuring a balanced fatty acid composition containing either linoleic acid (18:2 n-6) or linolenic acid (18:3 n-3) as sole polyunsaturated fatty acid source. Transmembrane potentials were monitored with microelectrodes and contractions with a photoelectric device. The radio of n-6 to n-3 phospholipid fatty acids increased from 6.3 in control cells to 20.2 in cells exposed to n-6 fatty acids (SM6) and decreased to 1.4 in those exposed to n-3 fatty acids (SM3). These modifications had no influence on the electrical and mechanical activities and on automaticity in normoxic conditions. The action potential depression under hypoxia was less severe in SM6 cells, whereas there was a better electrophysiological recovery upon reoxygenation in SM3 cells. However, the loss of lactate dehydrogenase during sustained hypoxic treatment was not affected by changes in phospholipid fatty acid pattern. These results suggest that the effect of the polyunsaturated fatty acid balance depends on the cellular function under study and on the environmental conditions.