Oliveira EM, Vassallo DV, Sarkis JJ

Mercury effects on the contractile activity of isolated heart muscle

Toxicol Appl Pharmacol, 1:86-91, 1994 Sep

Abstract: The toxic effects of HgCl2 (1, 2.5, 5, and 10 microM) were
studied in isolated, isometrically contracting rat papillary muscles and
frog ventricular strips. In rat papillary muscles 1 microM Hg2+ produced
a small increase in the force of contraction. Higher concentrations of HgCl2
produced a dose-dependent decrease in contractile force. The rate of
force development was affected differently, increasing at 1 and 2.5 microM
Hg2+ and decreasing to control levels at 5 and 10 microM Hg2+. This
was the result of a progressive reduction in the time to peak tension
observed when HgCl2 concentrations increased. This effect probably
reflects the binding of Hg2+ to SH groups inducing Ca2+ release from the
sarcoplasmic reticulum. The relative potentiation of postrest
contractions was used as an index of sarcoplasmic reticulum activity. It was
measured after pauses of increasing duration and was reduced at
concentrations of 1 microM Hg2+ when compared to that of the control. A
further decrement in the relative potentiation was observed with 
higher Hg2+ concentrations, indicating that the activity of the 
sarcoplasmic reticulum was depressed by mercury in a 
dose-dependent manner. Tetanic contractions were also studied 
in the rat myocardium. The tetanic tension did not
change during treatment with 1 microM Hg2+ but decreased with 5
microM Hg2+, suggesting a toxic effect on the contractile 
proteins only at high Hg2+ concentrations. 

Frog ventricular strips were studied using the
same HgCl2 concentrations and no effects on either force or relative
potentiation were observed. These findings suggest that Hg2+ promotes
dose-dependent toxic effects on heart muscle via actions on 
the sarcolemma, the sarcoplasmic reticulum, and contractile proteins.

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