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 distribution of this ion in sperm cells have not been explored. In rat spermatids, our results indicate that 1) ⁶⁵Zn(II) binds with fast kinetics to a labile, presumably extracellular, compartment. This binding is temperature insensitive and not modified by metabolic inhibitors. 2) Entry of ⁶⁵Zn(II) in the absence of externally added proteins occurs through a mediated transport system that allows exchange to reach steady state in ~15 min at 34°C. 3) Upon entering the cells, ⁶⁵Zn(II) binds tightly to cellular organelles. 4) Exchangeable Zn(II) bound to cytoplasmic proteins plus free intracellular Zn(II) appears to be <20% of total exchangeable Zn(II). 5) The intracellular exchangeable Zn(II) compartment is decreased by metabolic inhibitors, showing a direct or indirect link between energy metabolism and cellular Zn(II) levels. 6) ⁶⁵Zn(II) efflux from rat spermatids is a process with a rate constant of 0.16 ± 0.13 min^-1 at 34°C. This exit rate of Zn(II) is likely to be affected by Zn(II) release from cytoplasmic binding sites or organelles.