The Influence of D 600, Ouabain, and Calcium on the Post-Rest Adaptation in Guinea Pig Papillary Muscle

Abstract

In guinea pig papillary muscle, the force of contraction and the action potentials showed characteristic patterns of adaptation after various periods of rest. These patterns could be influenced by pharmacological agents. After 10 min of rest, the contraction amplitude was small. At 1 Hz the force of contraction increased monotonically to reach pre-rest control values within 3–5min. The post-rest changes of the action potential duration (a.p.d.) on the other hand were biphasic. Starting from a first action potential which was clearly longer than the pre-rest value, the duration of the consecutive action potentials increased rapidly, reached a maximum, and then declined slowly to the control level. The time course of the post-rest adaptation of the a.p.d. could be described by the sum of two exponential functions, each of which being regarded as a cumulation curve. This suggests the presence of two indepent and opposing processes, one prolonging and the other one shortening the a.p.d. They were called the lengthening and shortening effect of activation (LEA and SEA, respectively). Two similar opposing processes during activation have been described for the post-rest changes in mechanical activity by KOCHWESER and BLINKS (1963).