AUTOMETALLOGRAPHIC DEMONSTRATION OF ZINC IONS IN RAT SPERM CELLS

An in-vitro technique for autometallographic (AMG) demonstration of ch elatable zinc in electroejaculated sperm cells and spermatozoa from th e epididymis is presented and the localization of zinc ions in rat spe rmatozoa is described. Sperm cells from caput epididymis showed zinc s taining in all parts of the tail and a sparse, dispersed staining in t he acrosome. Spermatozoa from cauda epididymis showed heavy staining i n the acrosome but no staining in the tail, or post-acrosomal part of the sperm head. This distinct acrosomal AMG staining was also found in ejaculated spermatozoa, but additionally a segmentation of the tail w as seen based on differences in staining intensity. The membrane penet rating chelator diethyldithiocarbamate (DEDTC) was found to block the AMG staining whereas calcium-EDTA, known not to pass through cell memb ranes, did not influence the staining, proving that the detected zinc ions are intracellularly located. Two different approaches for demonst rating the presence of a chelatable zinc pool at electron microscope l evels are presented, and the ultrastructural presence of AMG grains lo cated in the acrosome and in the mitochondria of the midpiece is demon strated. It is postulated that an exchange of zinc ions takes place be tween the epididymal epithelium and the sperm cells as they pass along the epididymal duct.