Effects of hypoxia and acute osmotic stress on intermediary metabolism in Leishmania promastigotes

Abstract

This study further explores the effects of hypoxia and acute osmotic stress on intermediary metabolism of Leishmania major and Leishmania donovani. Late log phase promastigotes were washed and incubated with glucose as the sole exogenous carbon source, and rates of glucose consumption and product formation were measured as a function of osmotic strength (610, 305, and 167 mOsm kg 1) and pO 2 (95, 10, and 0% O 2) in the presence of 5% CO 2. Very mild hypoxia dramatically altered flux through the pathways of intermediary metabolism and increased the rates of production of the major metabolites, thus confirming the presence of a low-affinity O 2 sensor which was active under all osmolalities tested. The data also require that as pO 2 is lowered towards anoxia an endogenous carbohydrate source is mobilized. Under aerobic conditions, acute hypo-osmotic stress had little effect on product formation, whereas acute hyperosmotic stress altered metabolism in a manner similar to mild hypoxia, with the exception of decreasing the rates of acetate and succinate production. It was also shown in L. donovani promastigotes that the effects of anoxia and hyperosmolality were not additive. Thus, separate sensors with partially overlapping actions are involved in the metabolic responses to hypoxia and hyperosmolality. There was no apparent species-specificity for the responses to pO 2 and osmotic stress. Uncoupling with carbonyl cyanide p-trifluoromethoxyphenylhy-drazone caused changes in metabolite flux patterns which differed from the changes caused by either hypoxia or acute osmotic stress, while rotenone and calcium ionophore A23187 had no significant effects. The identity of the sensors responsive to pO 2 and osmolality, and the mechanisms by which they regulate flux through the pathways of intermediary metabolism, require further study.