Suppression of calcium sparks in rat ventricular myocytes and direct inhibition of sheep cardiac RyR channels by EPA, DHA and oleic acid

The anti-arrhythmic effects of long-chain polyunsaturated fatty acids (PUFAs) may be related to their ability to alter calcium handling in cardiac myocytes. We investigated the effect of eicosapentanoic acid (EPA) and docosahexaenoic acid (DHA) on calcium sparks in rat cardiac myocytes and the effects of these PUFAs and the monounsaturated oleic acid on cardiac calcium release channels (RyRs). Visualization of subcellular calcium concentrations in single rat ventricular myocytes showed that intensity of calcium sparks was reduced in the presence of EPA and DHA (15 pm). It was also found that calcium sparks decayed more quickly in the presence of EPA but not DHA. Sarcoplasmic vesicles containing RyRs were prepared from sheep hearts and RyR activity was determined by either [3 H]ryanodine binding or by single-channel recording. Bilayers were formed from phosphatidylethanolamine and phosphatidylcholine dissolved in either n-decane or n-tetradecane. EPA inhibited [H-3]ryanodine binding to RyRs in SR vesicles with K-I = 40 muM. Poly- and mono-unsaturated free fatty acids inhibited RyR activity in lipid bilayers. EPA (cytosolic or luminal) inhibited RyRs with K-I =32 muM and Hill coefficient, n(1) = 3.8. Inhibition was independent of the n-alkane solvent and whether RyRs were activated by ATP or Ca2+. DHA and oleic acid also inhibited RyRs, suggesting that free fatty acids generally inhibit RyRs at micromolar concentrations.