Temperature dependence of intracellular Ca2+ homeostasis in rat meiotic and postmeiotic spermatogenic cells

The hypothesis that intracellular [Ca2+] is a cell parameter responsive to extreme temperatures in rat meiotic and postmeiotic spermatogenic cells was tested using intracellular fluorescent probes for Ca2+ and pH. In agreemen t with this hypothesis, extreme temperatures induced a rapid increase of cy tosolic [Ca2+] in rat pachytene spermatocytes and round spermatids. Oscilla tory changes in temperature can induce oscillations in cytosolic [Ca2+] in these cells. Intracellular [Ca2+] homeostasis in round spermatids was more sensitive to high temperatures compared with pachytene spermatocytes. The c alculated activation energies for SERCA ATPase-mediated fluxes in pachytene spermatocytes and round spermatids were 62 and 75 kj mol(-1), respectively . The activation energies for leak fluxes from intracellular Ca2+ stores we re 55 and 68 kj mol(-1) for pachytene spermatocytes and round spermatids, r espectively. Together with changes in cytosolic [Ca2+], round spermatids un dergo a decrease in pH(i) at high temperatures. This temperature-induced de crease in pH(i) appears to be partially responsible for the increase in cyt osolic [Ca2+] of round spermatids induced by high temperatures. This charac teristic of rat meiotic and postmeiotic spermatogenic cells to undergo an i ncrement in cytosolic Ca2+ at temperatures > 33 degreesC can be related to the induction of programmed cell death by high temperatures in these cells.