Tricyclic hydrocarbon fluorene attenuates ventricular ionic currents and pressure development in the navaga cod

The release of polycyclic aromatic hydrocarbons (PAHs) into the environment due to oil and diesel fuel spills is a serious threat to Arctic fish populations. PAHs produce multiple toxic effects in fish, but disturbance of electrical and contractile activity of the heart seems to be the most negative effect. Our study focused on the effects of fluorene, a tricyclic PAH resembling the well-investigated tricyclic phenanthrene, on major ionic currents and action potential (AP) waveform in isolated ventricular myocytes and on contractile activity in isolated whole hearts of polar navaga cod (Eleginus nawaga). Among the studied currents, the repolarizing rapid delayed rectifier K+ current IKr demonstrated the highest sensitivity to fluorene with IC50 of 0.54 mu M. The depolarizing inward currents, INa and ICaL, were inhibited with 10 mu M fluorene by 20.2 +/- 2.8 % and 27.9 +/- 8.4 %, respectively, thereby being much less sensitive to fluorene than IKr. Inward rectifier IK1 current was insensitive to fluorene (up to 10 mu M). While 3 mu M fluorene prolonged APs, 10 mu M also slowed the AP upstroke. Resting membrane potential was not affected by any tested concentrations. In isolated heart experiments 10 mu M fluorene caused modest depression of ventricular contractile activity. Thus, we have demonstrated that fluorene, a tricyclic PAH present in high quantities in crude oil, strongly impacts electrical activity with only slight effects on contractile activity in the heart of the polar fish, the navaga cod.