Effects of mercury on the mechanical and electrical activity of the Langendorff-perfused rat heart

RESUMO

The effects of increasing concentrations of mercury (Hg2+) chloride (0.5, 1, 2 and 10 uM) on the myocardial electromechanical activity were studied on 10 Langendorff-perfused rat hearts. Hg2+ decreased the development of isovolumic systolic pressure from 20.3 ñ 2.13 mmHg under control conditions to 6.25 ñ 1.32 mmHg at 10 uM HgCl2 (P<0.01) (diastolic pressure = 0 mm Hg). The atrial and ventricular rates also decreased at uM, 1 uM and 2 uM HgCl2 when compared to the Hg2+ - free solution (from 201 ñ 4 to 126 ñ 15 bpm). However, at 10 uM Hg2+ the atrial rate increased (155 ñ 19 bpm) whereas the ventricular rate did not change significantly (119 ñ 13 bpm). A delay in atrioventricular conduction occured at 0.5 uM Hg2+ (64 ñ 4 ms in the Hg2+ free solution to 91 ñ 14 ms in the presence of 0.5 uM Hg2+, P<0.05) with no further changes at higher Hg2+ concentrations. The QRS-T duration also increased as a function of increasing Hf2+ concentrations (58 ñ 5.5 ms in the Hg2+ -free solution to 123 ñ 15 ms in the presence of 10 uM Hg2+ , P<0.01). Qualitative changes of ECG such as extrasystoles , atrial or ventricular arrhythmias and A-V blocks were also observed. The inhibitory action of Hg2+ on ATP hydrolysis and on Ca2+ and Na+-K+ ATPases suggested to occur in other tissues could be the mechanism responsible for the observations reported here