Effects of epoxyeicosatrienoic acids on the cardiac sodium channels in isolated rat ventricular myocytes

1. Whole-cell Na+ currents (holding potential, -80 mV; test potential, -30 mV) in rat myocytes were inhibited by 8,9-epoxyeicosatrienoic acid (8,9-EET) in a dose-dependent manner with 22 +/- 4% inhibition at 0.5 mu M, 48 +/- 5% at 1 mu M, and 73 +/- 5% at 5 mu M (mean +/- S.E.M., n =10, P < 0.05 for each dose vs. control). Similar results were obtained with 5,6-, 11,12-, and 14,15-EETs, while 8,9-dihydroxyeicosatrienoic acid (DHET) was 3-fold less potent and arachidonic acid was 10- to 20-fold less potent. 2. 8,9-EET produced a dose-dependent, hyperpolarized shift in the steady-state membrane potential at half-maximum inactivation (V-1/2), without changing the slope factor. 8,9-EET had no effect on the steady-state activation of Naf currents. 3. Inhibition of Na+ currents by 8,9-EET was use dependent, and channel recovery was slowed. The effects of 8,9-EET were greater at depolarized potentials. 4. Single channel recordings showed 8,9-EET did not change the conductance or the number of active Na+ channels, but markedly decreased the probability of Na+ channel opening. These results were associated with a decrease in the channel open lime and an increase in the channel closed times. 5. Incubation of cultured cardiac myocytes with mu M [H-3]8,9-EET showed that 25% of the radioactivity was taken up by the cells over a 2h period, and most of the uptake was incorporated into phospholipids, principally phosphatidylcholine. Analysis of the medium after a 2 h incubation indicated that 86% of the radioactivity remained as [3H]8,9-EET while 13% was concerted into [H-3]8,9-DHET. After a 30 min incubation, 1-2% of the [3H]8,9-EET uptake by cells remained as unesterified EET. 6. 6. These results demonstrate that cardiac cells have a high capacity to take up and metabolize 8,S-EET. 8,S-EET is a potent use- and voltage-dependent inhibitor of the cardiac Na+ channels through modulation of the channel gating behaviour.