Sarcomere dynamics in isolated cardiac myocytes investigated by high-time resolution laser light diffractometry

Unattached single cells of the guinea pig myocardium were illuminated with laser light. From the position of the mean of the first order diffraction line at a CCD sensor the sarcomere length was calculated with a time resolution of 1 ms. The maximum velocity of the sarcomere shortening was 2.15 +/- 0.87 microns/s (mean +/- S.E.). Nearly 20% of the cells investigated were found to shorten in a stepwise manner. The intensity profiles of these myocytes deviated from the Gaussian shape at the same time as "pauses" became visible. Therefore, this phenomenon might be due to Bragg effects which result from different sarcomere populations within stepwise shortening cardiac cells.