Stress response to high osmolarity in Trypanosoma cruzi epimastigotes

Abstract

Trypanosoma cruzi undergoes differentiation in the rectum of triatomine, where increased osmolarity is caused mainly by elevated content of NaCl from urine. Early biochemical events in response to high osmolarity in this parasite have not been totally elucidated. In order to clarify the relationship between these events and developmental stages of T. cruzi, epimastigotes were subjected to hyperosmotic stress, which caused activation of Na+/H+ exchanger from acidic vacuoles and accumulation of inositol trisphosphate (InsP3). Suppression of InsP3 levels was observed in presence of intracellular Ca2+ chelator or pretreatment with 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), which also inhibited the alkalinization of acidic vacuoles via a Na+/H+ exchanger and the consequent increase in cytosolic calcium. These effects were activated and inhibited by PMA and Chelerythrine respectively, suggesting regulation by protein kinase C. The T. cruzi Na+/H+ exchanger, TcNHE1, has 11 transmembrane domains and is localized in acidic vacuoles of epimastigotes. The analyzed biochemical changes were correlated with morphological changes, including an increase in the size of acidocalcisomes and subsequent differentiation to an intermediate form. Both processes were delayed when TcNHE1 was inhibited by EIPA, suggesting that these early biochemical events allow the parasite to adapt to conditions faced in the rectum of the insect vector.