Morphologic and morphometric analysis of the mast cells from human heart biopsies.

We have examined mast cell morphology in human papillary muscles obtained from patients subjected to mitral valve replacement. Elongated, metachromatically staining mast cells were found in the connective tissue close to blood vessels and nerves. Electron microscopic examination showed that the most conspicuous features were cytoplasmic granules which displayed a crystalline internal structure and which were surrounded by perigranular membranes. They were composed of a number of coiled electron-dense layers (3 to 4 predominantly) which formed scrolls and gratings. Apart from the crystalline structure, all granules had a dark, uniform matrix. Measurements of crystalline structure periodicity indicated a unimodal distribution around a mean of 85.6 +/- 1.9 A.