ZN(II) TRANSPORT AND DISTRIBUTION IN RAT SPERMATIDS

Zn(II) is an essential trace element. In spermatozoa, Zn(II) modulates metabolism and chromatin condensation. The mechanisms of uptake and d istribution of this ion in sperm cells have not been explored. In rat spermatids, our results indicate that 1) Zn-65(II) binds with fast kin etics to a labile, presumably extracellular, compartment. This binding is temperature insensitive and not modified by metabolic inhibitors. 2) Entry of Nn-65(II) in the absence of externally added proteins occu rs through a mediated transport system that allows exchange to reach s teady state in approximately 15 min at 34-degrees-C. 3) Upon entering the cells, Zn-65(II) binds tightly to cellular organelles. 4) Exchange able Zn(II) bound to cytoplasmic proteins plus free intracellular Zn(I I) appears to be <20% of total exchangeable Zn(II). 5) The intracellul ar exchangeable Zn(II) compartment is decreased by metabolic inhibitor s, showing a direct or indirect link between energy metabolism and cel lular Zn(II) levels. 6) Zn-65(II) efflux from rat spermatids is a proc ess with a rate constant of 0.16 +/- 0.13 min-1 at 34-degrees-C. This exit rate of Zn(II) is likely to be affected by Zn(II) release from cy toplasmic binding sites or organelles.