An in vitro assay for the assessment of the effects of an organophosphate, paraoxon, and a triazine, atrazine, on the heart of the gilthead sea bream (Sparus aurata)

The effects of paraoxon and atrazine on the spontaneously beating auricle, isolated from the heart of Sparus aurata, were assessed. Paraoxon, 5 μM, eliminated the atria contraction within 28.4 ± 2.8 min, an effect which was fully reversed by 15 μM atropine, an antagonist of muscarinic cholinergic receptors. The IC₅₀ was estimated to be 3.2 ± 1.5 μΜ. Atrazine, 50 and 100 μM, induced a 22.5 ± 3.2 and 32.9 ± 2.3% increase in the force of auricle contraction, caused by excitation of sympathetic synaptic terminals releasing adrenaline. This effect was reversed by 50 μM propranolol, a blocker of β-adrenoreceptors. The results have shown that both sympathetic and parasympathetic nerve terminals are activated by atrazine. Also, the auricle contraction is mainly under sympathetic control, while the frequency is dominated by cholinergic system. Finally, the detailed parameters of the auricle contraction estimated during exposure to specific pesticides, force, frequency, time-response curves and electromechanical coupling can be further used to assess and compare the toxic effects of other compounds, anticholinesterases for example, on the heart of the fish.