Comparison of the calcium distribution pattern among several kinds of hard tissue forming cells of some living vertebrates.

We investigated the ultrastructural distribution of calcium in several kinds of hard tissue forming cells (secretory and maturation ameloblasts, odontoblasts osteoblasts, chondrocytes, and osteodentine forming cells) of mammals, amphibians, and fish by use of the potassium pyroantimonate technique. The calcium distribution pattern is compared among these cells, and its biological significance is discussed. Except for mammalian odontoblasts, all types of the hard tissue forming cells exhibited fundamentally the same distribution pattern of calcium; the antimonate reaction product was mainly localized on the inner face of the plasmalemma and inside mitochondria. On the other hand, in mammalian odontoblasts, the reaction product was found within secretory granules and in the intercellular spaces. Thus, the calcium distribution pattern in odontoblasts of lower vertebrates differed from that of mammalian odontoblasts and was similar to that of the osteoblasts or chondrocytes of the vertebrates examined. The differences in calcium distribution pattern among these hard tissue forming cells were not related to their origin, ectodermal or mesodermal (ectomesenchymal). We suggest on the basis of previous studies cited in this paper and of the present data that they are closely associated with the phylogeny and physiological system of Ca-ATPase.