Influence of temperature on lactate utilization by round spermatids from rat testes

Rotenone-sensitive ¹⁴CO₂ formation from [¹⁴C]lactate and oxygen consumption by round spermatids were found to be greater at elevated temperatures than at 34°C. More than 96% of the total radioactivity of the metabolized [¹⁴C]lactate was recovered in the released CO₂ and the acid soluble fraction of the cells. There was practically no incorporation of [¹⁴C]lactate into the lipid, nucleic acid, and protein fractions. Intracellular level of ATP in spermatids was enhanced in the presence of lactate (20 mM) at 34°C (scrotal temperature), whereas it was decreased at 37°C (body temperature). However, this was reversible when the cells were transferred from the elevated temperature to 34°C. It was also found that oxygen consumption and CO₂ production were increased at 34° C by 2,4-dinitrophenol (DNP), but decreased by oligomycin. On the contrary, oligomycin and DNP had no effect on oxygen consumption and ¹⁴CO₂ formation at the elevated temperature. These findings provide evidence that lactate utilization by spermatids is coupled with oxidative phosphorylation at scrotal temperature, but becomes uncoupled at elevated temperature, although more lactate is consumed.