Shortening-Deactivation and Stretch-Activation During Spontaneous Contraction and Relaxation of Bivalve Cardiac Muscles

Shortening-deactivation and Stretch-activation are well established techniques to study the dynamics of muscles. However, very limited data exists for comparing the two techniques. This study was conducted to perform stretch and release on the same muscle specimen and to determine whether a correlation exists between the two data sets. The entire heart of the clam (Venus mercenaria) was used in a muscle bath preparation. The neurotransmitter 5-hydroxytryptamine (5HT) was used to modulate the cardiac rhythmicity. Stretch-activation and shortening-deactivation at different phases of a spontaneous contraction cycle were introduced by used a computer-controller lever system. A preliminary analysis based on the time integral of the deviation of a perturbed force curve from the normal curve did not show a significant correlation between stretch-activation and shortening-deactivaton. Future study will include additional experiments and more sophisticated model-based analyses.