Effects of mercury on the contractility of isolated rat cardiac muscle.
The effects of increasing concentrations of mercury (Hg2+) chloride (1, 2.5, 5 and 10 microM) were studied on isometrically contracting papillary muscles from female rats (Wistar, EPM strain) weighing 150 to 180 g. Hg2+ promoted an increase of 12.7 +/- 2.2% in the developed force at 1 microM. At 2.5 microM, force values were similar to control, decreasing progressively as Hg2+ concentration increased to 5 (-13 +/- 6.4%) and 10 microM (-37 +/- 12.3%). Potentiated post-rest contractions (PRC) were also determined after 15-, 30- and 60-s pauses. There was a progressive reduction of the potentiated PRCs relative to their respective steady-state control contractions with increasing concentrations of HgCl2. Since in several tissues including myocardium Hg2+ inhibits the activity of Ca2+ and Na(+)-K(+)-ATPases the results described here suggest that Hg2+, at lower concentrations, could increase force by inhibiting Na(+)-K(+)-ATPase, while at higher concentrations Hg2+ would decrease relative PRC potentiation by inhibiting sarcoplasmic reticulum Ca(2+)-ATPase.
Oliveira
E M
EM
Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, Brasil.
Vassallo
D V
DV
D000704:Analysis of Variance; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008627:Mercuric Chloride / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013997:Time Factors
D008627:Mercuric Chloride; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase