Effects of amrinone on contraction and K+-induced contracture of normal and subacutely failed cat ventricular muscle.

Normal right ventricular muscles and similar preparations obtained from cats with signs of subacute right ventricular failure (RVF) (3 to 14 days after pressure overload induced by pulmonary artery coarctation) were studied during stimulation (at 0.5 Hz) and exposure to high-K+ Tyrode's solution. Twitch force, rate of force development (dP/dt), and rate of relaxation (-dP/dt) were significantly lower in RVF muscles compared with control muscles; duration of the twitch was significantly longer. Time to peak force was unchanged. Amrinone (5.3 x 10(-4)M) increased twitch force and dP/dt in normal muscle; however, the drug had no significant effects on twitch force and dP/dt in RVF muscles. Also unlike its action in control muscle, duration of the twitch was reduced by amrinone in failed muscle. Amrinone reduced K+ contracture force similarly in control and RVF muscle. In control and RVF muscles, isoproterenol (1.0 x 10(-6)M) significantly increased twitch force and dP/dt and reduced K+ contracture, while ouabain increased twitch force, dP/dt, and K+ contracture. The differential effects of amrinone on RVF and control muscles may reflect cellular defects associated with experimental ventricular failure.