OSMOTIC AND METABOLIC-INDUCED CHANGES IN LIGHT-SCATTERING OF LEISHMANIA-DONOVANI AS MEASURED BY FLOW-CYTOMETRY

Leishmania donovani promastigotes were collected from cultures in log and stationary phases of growth and resuspended in Hank's Balanced Sal t Solution containing 1 mM sodium acetate. Changes in the forward and side scattering of the cells were measured by flow cytometry in respon se to acute changes in osmolality and to the addition of several diffe rent substrates. Forward and side scattering of cells from log phase c ultures decreased when the osmolality was decreased by the addition of H2O and increased when the osmolality was increased by the addition o f NaCl. Cells from stationary phase cultures had about the same forwar d scatter as cells from log phase cultures, but almost a four-fold low er side scatter, and their side scatter values did not change signific antly in response to a reduction in osmolality. Microscopic observatio n showed that both log and stationary cells got longer and thinner, on average, in response to hyperosmolality. The light scattering propert ies of log (but not of stationary) cells changed in a reproducible man ner when substrates were added to the buffer. The ratio of forward to side scatter increased in the following order: controls in balanced sa lt solution < aspartate < glutamate, glucose or 2-deoxyglucose < alani ne < proline. Thus the light scattering properties of L. donovani prom astigotes change with culture age, in response to changes in osmolalit y, and, in log phase cells, in response to the presence of several sub strates.