Abstract

Intracellular crystallization processes occurring in cultured pheochromocytoma cells induced by ascorbic acid were characterized at the atomic level by means of high-resolution electrón microscopy (HREM). A series of HREM observations revealed various stages of crystallization processes occurring in the amorphous matrix of the dense bodies of the cells. By day 5 in culture, the dense bodies were shown to consist of randomly packed clusters of the atom-sized dots about 0.16 x 0.23 nm in size. These dots were close-packed to form different sized clusters of very fine dot-like crystals and microcrystallites at day 7 and 10 in culture respectively. At day 14 in culture, the perfect crystals in a hexagonal form were often present in the dense bodies. High-resolution images of the lattice structures in the crystals showed that the atom-sized dots about 0.18 x 0.23 nm in size were regularly arranged in a hexagonal array with center-to-center spacing of 0.26 nm. Energy-dispersive X-ray microanalysis of isolated microcrystal from the cultured cells consistently detected the presence of the mineral elements such as phosphorus and calcium. X-ray mapping showed that calcium element was densely and evenly distributed in the crystals. We have succeeded in creating a cultured cell model for the investigation oí intracellular crystallization processes at the atomic level. The deposition of the mineral elements, particularly calcium, has suggested being effective for the initiation of crystallization processes or at least the transformation of the amorphous nucleation phase to a well-crystallized nucleation phase. it is hoped that such information obtained from the HREM observations has provided direct insight into the mechanisms of biological tissue crystallization