Cyclic AMP-dependent modulation of cardiac L-type Ca2+ and transient outward K+ channel activities by epoxyeicosatrienoic acids.

The three major enzyme systems, cyclo-oxygenase, lipoxygenase, and cytochrome P450 (P450/CYP), metabolize arachidonic acid (AA) to biologically active compounds. P450 and its associated monooxygenase activities have been identified in mammalian cardiac tissue, including humans. The four regioisomeric eicosanoids, 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs) of AA metabolites derived by P450 epoxygenases have shown to possess potent biological effects in numerous tissues. In the coronary circulation the EETs are leading candidates for endothelial-derived hyperpolarizing factors that hyperpolarize vascular smooth muscle cells by opening Ca2+-activated K+ channels. Recently, the effects of the CYP pathways and their metabolites on cardiac ischemia-reperfusion injury have been evaluated in animal models. Some of these AA metabolites are cardioprotective and some are detrimental. However, EETs appear to be cardioprotective in CYP2J2 transgenic mice and in a canine ischemic model. Multiple effects of EETs on cardiac ion channels have been observed, such as activation of ATP-sensitive K+ channels and L-type Ca2+ channels in cardiomyocytes and inhibition of cardiac Na+ channels and L-type Ca2+ channels reconstructed in planar lipid bilayers. This brief review summarizes EET-induced modulation of cardiac ion channels.