Em. Oliveira et al., MERCURY EFFECTS ON THE CONTRACTILE ACTIVITY OF ISOLATED HEART-MUSCLE, Toxicology and applied pharmacology, 128(1), 1994, pp. 86-91
The toxic effects of HgCl2(1, 2.5, 5, and 10 mu M) were studied in iso
lated, isometrically contracting rat papillary muscles and frog ventri
cular strips. In rat papillary muscles 1 mu M Hg2+ produced a small in
crease in the force of contraction. Higher concentrations of HgCl2 pro
duced a dose-dependent decrease in contractile force. The rate of forc
e development was affected differently, increasing at 1 and 2.5 mu M H
g2+ and decreasing to control levels at 5 and 10 mu M Hg2+. This was t
he result of a progressive reduction in the time to peak tension obser
ved when HgCl2 concentrations increased. This effect probably reflects
the binding of Hg2+ to Sc groups inducing Ca2+ release from the sarco
plasmic reticulum. The relative potentiation of postrest contractions
was used as an index of sarcoplasmic reticulum activity. It was measur
ed after pauses of increasing duration and was reduced at concentratio
ns of 1 mu M Hg2+ when compared to that of the control. A further decr
ement in the relative potentiation was observed with higher Hg2+ conce
ntrations, indicating that the activity of the sarcoplasmic reticulum
was depressed by mercury in a dose-dependent manner. Tetanic contracti
ons were also studied in the rat myocardium. The tetanic tension did n
ot change during treatment with 1 mu M Hg2+ hut decreased with 5 mu M
Hg2+, suggesting a toxic effect on the contractile proteins only at hi
gh Hg2+ concentrations. Frog ventricu; lar strips were studied using t
he same HgCl2 concentrations and no effects on either force or relativ
e potentiation were observed. These findings suggest that Hg2+ promote
s dose-dependent toxic effects on heart muscle via actions on the sarc
olemma, the sarcoplasmic reticulum, and contractile proteins. (C) 1994
Academic Press, Inc.