Histochemistry (1983) 78 : 435-449 Histochemistry Springer-Verlag 1983 Application of Optical Diffraetometry in Studies of Cell Fine Structure Comparison of Arterial Smooth Muscle Cells in Contractile and Synthetic State K. Ostrowski ~, J. Thyberg 3., A. Dziedzic-Goclawska z, M. Rozycka I, S. Lenczowski 1, T. Ksiazek 3, J. Nilsson 3, L. Palmberg 3, and M. Sj61und 3 Departments of 1 Histology and z Transplantology, Medical School, PL-02-004 Warsaw, Poland, and 3 Department of Histology, Karolinska Institutet, Box 60400, S-104 01 Stockholm, Sweden Summary. Arterial smooth muscle cells in contractile and synthetic state were analyzed by optical diffractometry. Cell sections (80-90 nm) were photographed in an electron microsope and diffraction patterns of the plates (negatives) were produced using a helium-neon laser. Radial and angular distributions of light intensity in the diffractograms were mea- sured and digitized using an electronic detector plate consisting of ring- and wedge-shaped photosensitive elements; radial distributions provide information about size of structures and distances between them and angular distributions about spatial orientation of structures in the im- ages. Micrographs of nuclei and cytoplasm were analyzed separately (40-50 plates in each group). Computerized statistical analysis of radial distributions of light intensity showed that the nuclear chromatin pattern differed between cells in contractile and synthetic state. The probability that the observed difference could have arisen purely by chance was less than 10 -5. Computer-aided classification to the a priori known cell group was correct in 96.5% of the cases. Analysis of radial distribu- tions of light intensity similarly showed marked differences in cytoplas- mic structure between cells in contractile state (dominated by bundles of myofilaments) and synthetic state (dominated by cisternae of rough endoplasmic reticulum). The probability that the observed difference could have arisen purely by chance was less than 10-5. Computer-aided classification to the a priori known cell group was correct in 92.0% of the cases. In contrast, analysis of angular distributions of light intensi- ty did not indicate any statistically significant differences between con- tractile and synthetic state cells. A likely reason is that both myofilaments and cisternae of rough endoplasmic reticulum were arranged in parallel. The results demonstrate that optical diffractometry is a useful method for image analysis in studies of cell fine structure. It provides information about size and orientation of structures with poorly defined shape and * To whom offprint requests should be sent