The impact of glycolysis on rat spermatid energy metabolism is made apparent by the simultaneous occurrence of the following three events upon glucose addition to the extracellular medium of a rat spermatid cell suspension: decrease in ATP content, exit of acid equivalents, and increased lactate production and efflux. In this work, we have studied the interrelations between these three phenomena. By measuring ATP content, net acid transport, lactate exit, oxygen consumption, intracellular pH, CO2 production, and glycolytic intermediates in the presence of glucose and glucose analogues, we conclude that 1) lactate production, decrease in ATP content, and acid equivalent exit are dependent on the metabolism of glucose up to different stages in glycolysis. 2) The decrease in ATP content is not directly related to the exit of acid equivalents from rat spermatids. 3) Glucose metabolism is a net ATP-consuming process at high intracellular ATP content but is a net ATP-producing process at low intracellular ATP concentration in rat spermatids. 4) Acid equivalent production arises from the metabolism of glucose beyond glyceraldehyde 3-phosphate dehydrogenase. 5) Lactic acid diffusion and/or lactate transport and CO2 production and exit could account for the glucose-dependent acid equivalent efflux in rat spermatids.
Effects of d-glucosamine and glucose analogues on glycogen biosynthesis in vitro