UPTAKE AND RELEASE OF 2-AMINOISOBUTYRATE BY LEISHMANIA-DONOVANI - CULTURE-AGE DEPENDENT EFFECTS OF OSMOLALITY AND OF PROTEIN-KINASE INHIBITORS

The rate of uptake of 2-aminoisobutyrate (AIB), a non-metabolizable an alogue of alanine, by Leishmania donovani was investigated as a functi on of culture age and osmolality in the presence of protein kinase inh ibitors and of glucose, glutamate or proline. Hyperosmolality inhibite d AIB uptake by cells of both growth stages, but to a greater extent f or log than for stationary cells. Staurosporine, a protein kinase C in hibitor, had no effect on AIB uptake by cells of either culture age, b ut it reduced the rate of AIB release in response to hypo-osmolality, and more so in stationary cells than in log cells. Genistein, a protei n-tyrosine kinase inhibitor, caused a small increase in AIB uptake by log cells under both iso- and hyperosmotic conditions, but had Ilo eff ect on AIB uptake by stationary cells. Genistein also caused a small i ncrease in the rate of release of AIB in response to a decrease in osm olality. Brief preincubation with glucose, glutamate or proline of cel ls that had been depleted of their osmolytes by prior exposure to hypo -osmolality caused an increase in AIB release by log cells, but a decr ease by stationary cells. Similarly, whereas glucose and glutamate inc reased the rate of AIB uptake by log cells, and proline inhibited it, they had no effect on ALE uptake by stationary cells. Thus AIB uptake and release are sensitive to changes in osmolality, to protein kinase inhibitors, and to certain nutrients in a manner that changes markedly with culture age.