Effects of iodoacetic acid on relaxation parameters of the rabbit papillary muscle.

Measurements have been made of isometric contractions and diastolic oscillations (after-contractions) in right ventricular rabbit papillary muscles at a temperature of 14.5 degrees C. The relaxation courses can be described as damped harmonic oscillations superposed on an exponential descending carrier function by using a model with six parameters. The influence of iodoacetic acid (10(-4) M) was investigated on contraction and relaxation parameters which result from approximation of the measured force values. The following changes were observed: 1. Decrease of the contraction height as well as of the amplitudes of diastolic oscillations. 2. Increase in the damping ratio and in the period of diastolic oscillations both calculated from relaxation parameters. 3. Diminution of the force range which is passed by the carrier function within 6 s of relaxation time accompanied by a transition to contracture. A fast and a slow Ca sequestration process are supposed to exist. The results indicate that both of them are influenced by iodoacetic acid.