Toxic effects of cadmium and copper on the isolated heart of dogfish shark, squalus acanthias

The adverse effects of heavy metal ions on the heart functions of lower vertebrates are largely unknown. In the present study, the effects of Cd²⁺, Cu²⁺, and Cu⁺ on the cardiac functions of the heart isolated from dogfish shark, Squalus acanthias, including the epicardial electrocardiogram, ventricular developed pressure (VDP), and heart beating rate, were studied. Cadmium (10 to 100 μM) significantly decreased VDP of the isolated shark hearts in a reversible manner. However, heart beating rate was not affected by cadmium. Cadmium also induced a transient modification of the amplitude and the form of the QRS complex. Cupric ion transiently increased VDP in a concentration-dependent manner, whereas cuprous ion (1 to 100 μM) did not markedly alter the cardiac functions of shark. Cupric or cuprous ions did not change heart beating rate and electrocardiogram at concentrations of 10 to 100 μM. Our results, for the first time, demonstrated the effects of cadmium on shark heart and indicated that the cardiac effects of copper are valence dependent. An elucidation of heavy metal effects on fish cardiac functions will help to understand the complex toxicological properties of heavy metals in different species and tissues, and will provide information for management of pollution control and marine resource protection.