Responses of a parasitic protozoan to osmotic stress

Leishmania major and L. donovani are parasitic protozoa that cause serious disease throughout the tropical and sub‐tropical regions of the world. They respond rapidly to osmotic stress. A sudden increase in osmolality causes a change in cell shape and an inhibition of the rates of oxidation of alanine, proline, and several other nutrients. A sudden decrease in osmolality also causes a change in shape (swelling) and extrusion of alanine and several other amino acids and of Na and Cl. The rate of release of amino acids in response to acute hypo‐osmolality is closely fit by a two exponential equation under a variety of conditions, such as the presence of activators or inhibitors of certain protein kinases and protein phospahatases and of arachidonic acid. These results are consistent with evidence suggesting the presence of two pools of alanine in Leishmania. Copyright © 2001 John Wiley & Sons, Ltd.