Effect of Manganese Ions on the Contraction and Automaticity of the Blood-Perfused Canine Papillary Muscle

Effect of manganese ions (Mn) on the mammalian ventricular myocardium was investigated using the isolated blood-perfused papillary muscle from the canine right ventricle. Mn caused dose-dependently an increase in blood flow above 0.1 mg and negative inotropic and chronotropic effects above 0.3 mg, while there was little change in the configuration of EMG even at a dose of 30 mg of Mn. The effects of Mn on the contraction and blood flow of the papillary muscle preparation were reversible. Norepinephrine, caffeine and calcium induced a positive inotropic effect almost to the same extent in the control or in the depressed state after Mn treatment, while periarterial nerve stimulation definitely caused a diminished increase in the contractile force after Mn treatment. Furthermore, in the automatically beating papillary muscle the positive chronotropic responses to norepinephrine and periarterial nerve stimulation were more readily blocked by Mn than the positive inotropic ones. These observations suggest that Mn affects not only contraction but also catecholamine release and pacemaker potential.