Ultrastructural distribution of calcium in the rat testis

Despite the important role of calcium in the growth and differentiation of a variety of cell types, its exact location and function in the somatic and germ cells of the testis remain to be determined. In the present study, we examined the subcellular distribution of calcium in the immature and adult rat testis. Calcium was localized at the electron microscopic level by ion-capture cytochemistry using combined oxalate and pyroantimonate procedures. Calcium-containing precipitates localized primarily within the nuclei, mitochondria, and cytosol of somatic and germ cells. Differences in the size and quantity of the calcium precipitates were observed among the various cellular compartments. In the somatic cells (Sertoli, Leydig, and myoid), the nuclei exhibited large round-shaped calcium-containing precipitates, whereas the mitochondria in these cell types contained numerous smaller precipitates. The cytoplasmic vesicles possessed single precipitates. These vesicles could be calciosomes, which have been described in other non-muscle cell types. Among germ cells, round spermatids exhibited a large number of vesicular, calsiosome-like structures in the cytoplasm containing single precipitates. The elongating spermatids from adult testis showed calcium localization within the nuclear matrix unassociated with the nuclear envelope, or in a peripheral alignment of precipitates along the nuclear envelope. Calciosome-like structures were also seen in round spermatids. Spermatogonia and spermatocytes exhibited calcium in nuclei, mitochondria, and cytoplasmic vesicles. These results demonstrate a differential distribution of calcium within the various cell types of the testis. The presence of calcium in the nucleus may suggest a role in cell growth and differentiation; calsiosome-like structures may represent the active exchangeable pool of calcium, and the differential type of distribution of calcium in elongating spermatids suggests a role for calcium in spermatid differentiation.