A calorimetric method to assess endogenous metabolism and its application to the study of bovine sperm

Calorimetry was used to assess the importance of endogenous metabolism towards total ATP synthesis in bovine sperm in the presence of extracellular glucose. Sperm were incubated in the calorimeter with D-[U-14C]glucose without or with electron transport inhibitors, rotenone and antimycin A. Steady-state heat production during the incubations was measured for 30 min, the incubations were terminated, and the cell suspensions removed for analysis of radioactive glucose and its metabolic end-products. Heat production (mean +/- S.E.) associated with the metabolism of glucose was calculated, from enthalpies of formation of glucose and its end-products, as -412 +/- 34 mJ/h/10(8) cells in control incubations and -263 +/- 18 mJ/h/10(8) cells in the incubations with electron transport inhibitors. Measured heat production was -455 +/- 36 and =263 +/- 17 mJ/h/10(8) cells, respectively. Thus, heat production by endogenous pathways, the difference between measured total heat production and calculated exogenous heat production, was -43 +/- 14 mJ/h/10(8) cells for control cells and about -6 mJ/h/10(8) cells for inhibited cells. The ratio of heat produced per mol of ATP synthesized is similar for all ATP-producing pathways. Therefore, about 10% of total ATP synthesis in control cells and less than 2% in inhibited cells is provided by endogenous pathways when extracellular glucose is present.