[Interaction between length and force in cardiac muscle. Electromechanical conjunction during myocardial deformation]

The influence of initial length upon the phasic and tonic components of contraction was investigated by modified sucrose gap method in myocardial specimens of frog atrium and ventriculum and in rabbit papillary muscles. The stretch of myocardial specimens was found to cause the shift in "current-force of contraction" curves towards lower values of depolarizing current. The relationship between phasic and tonic components was shown to depend upon the initial length of the heart muscle. It was suggested that changes in the membrane potential and proposed additional calcium activation play a major role in the myocardial length-tension relationship, as well as myofilaments overlapping.