Temperature-induced rapid increase in cytoplasmic free Ca²⁺ in pathogenic Leishmania donovani promastigotes

Abstract

We demonstrate that the cytoplasmic free Ca²⁺ concentration in three virulent Leishmania donovani promastigote strains is maintained at 20-30 nM level whereas the avirulent promastigotes maintain [Ca²⁺]_i at 80-100 nM. Rapid exposure of virulent promastigotes to higher physiological temperature increases [Ca²⁺]_i many-fold. Use of CaCl₂, EGTA and Mn²⁺ confirmed that both release of Ca²⁺ from internal pool(s) and influx from outside milieu are responsible for this increase in [Ca²⁺]_i. Application of oligomycin, CN^-, and nigericin indicated the non-mitochondrial pHi sensitive pool as the possible intracellular origin for internal Ca²⁺ release. Exposure of these cells to acidic environment had no influence on [Ca²⁺]_i. In contrast, the avirulent promastigotes or freshly isolated amastigotes had shown no effect of heat-shock or pH shock on [Ca²⁺]_i. of these cells. Our results indicate that the upward shift in temperature may play a role in signal transduction events in morphogenetic transformation of L. donovani promastigotes that involves mobilization of Ca²⁺ in cytoplasm.