ULTRASTRUCTURAL DISTRIBUTION OF CALCIUM IN THE RAT TESTIS

Despite the important role of calcium in the growth and differentiatio n of a variety of cell types, its exact location and function in the s omatic and germ cells of the testis remain to be determined. In the pr esent study, we examined the subcellular distribution of calcium in th e 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 locali zed primarily within the nuclei, mitochondria, and cytosol of somatic and germ cells. Differences in the size and quantity of the calcium pr ecipitates were observed among the various cellular compartments. In t he somatic cells (Sertoli, Leydig, and myoid), the nuclei exhibited la rge round-shaped calcium-containing precipitates, whereas the mitochon dria in these cell types contained numerous smaller precipitates. The cytoplasmic vesicles possessed single precipitates. These vesicles cou ld 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 sing le precipitates. The elongating spermatids from adult testis showed ca lcium localization within the nuclear matrix unassociated with the nuc lear envelope, or in a peripheral alignment of precipitates along the nuclear envelope. Calciosome-like structures were also seen in round s permatids. 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 rep resent the active exchangeable pool of calcium, and the differential t ype of distribution of calcium in elongating spermatids suggests a rol e for calcium in spermatid differentiation.