Comparison of the characteristics of the negative inotropic actions of dinitrophenol, rotenone, antimycin A and the intracellular calcium antagonist, propyl-methylenedioxyindene

The characteristics of the reversal of the comparable negative inotropic actions of 10(-4) M propyl-methylenedioxyindene (an intracellular calcium antagonist), 3 X 10(-5) M dinitrophenol (an uncoupler of mitochondrial oxidative phosphorylation), 10(-6) M rotenone (a site I mitochondrial respiratory chain poison) and 3 X 10(-6) M antimycin A (a site II mitochondrial respiratory chain poison) were studied in the isolated, electrically-paced guinea-pig left atrium. The negative inotropic effect of propyl-methylenedioxyindene was more sensitive to reversal by 5 mM calcium and 10(-9)-10(-7) M isoproterenol than were the comparable negative inotropic effects of dinitrophenol, rotenone and antimycin A. These results indicate that the negative inotropic effect of propyl-methylenedioxyindene is not exerted through inhibition of mitochondrial electron transport nor through uncoupling of mitochondrial oxidative phosphorylation.