Suppression of voltage-gated L-type Ca2+ currents by polyunsaturated fatty acids in adult and neonatal rat ventricular myocytes

Our recent data show that in cardiac myocytes polyunsaturated fatty acids (PUFAs) are antiarrhythmic. They reduce I-Na, shorten the action potential, shift the threshold for excitation to more positive potentials, and prolong the relative refractory period. In this study we use patch-clamp techniques in whole-cell mode and confocal Ca2+ imaging to examine the effects of PUFAs on the voltage-gated L-type Ca2+ current (I-Ca,I-L), elementary sarcoplasmic reticulum Ca2+-release events (Ca2+-sparks), and [Ca2+](i) transients in isolated rat ventricular myocytes. Extracellular application of eicosapentaenoic acid (EPA; C20:5 n - 3) produced a prompt and reversible concentration-dependent suppression of I-Ca,I-L. The concentration of EPA to produce 50% inhibition of I-Ca was 0.8 mu M in neonatal rat heart cells and 2.1 mu M in adult ventricular myocytes. While the EPA induced suppression of I-Ca,I-L, it did not significantly alter the shape of the current-voltage relation but did produce a small, but significant, negative shift of the steady-state inactivation curve. The inhibition of I-Ca,I-L was voltage- and time-dependent, but not use- or frequency-dependent. Other PUFAs, such as docosahexaenoic acid, arachidonic acid, linolenic acid, linoleic acid, conjugated linoleic acid, and eicosatetraynoic acid had similar effects on I-Ca,I-L as EPA. All-trans-retinoic acid, which had been shown to suppress induced arrhythmogenic activity in rat heart cells, also produced a significant inhibition of I-Ca,I-L. The saturated stearic acid and the monounsaturated oleic acid had no effect on I-Ca,I-L. Because both I-Ca,I-L and sarcoplasmic reticulum Ca2+-release underlie many cardiac arrhythmias, we examined the effects of EPA on I-Ca,I-L and Ca2+-sparks. While EPA suppressed both, it did not change the temporal or spatial character of the Ca2+-sparks, nor did it alter the ability of I-Ca,I-L to trigger Ca2+-sparks. We conclude that PUFAs may act as antiarrhythmic agents in vivo in normal and Ca2+-overloaded cells principally because they reduce Ca2+ entry by blocking I-Ca,I-L. Furthermore, PUFAs act directly to decrease I-Na and I-Ca,I-L, but indirectly to reduce the [Ca2+](i) transients and [Ca2+](i)-activated membrane current. Although a negative inotropic action is associated with application of PUFAs, it is clear that by reducing I-Ca,I-L, I-Na and Ca2+-sparks, PUFAs can reduce spontaneous extrasystoles in the heart. The mechanisms by which PUFAs act are discussed.