Temperature-induced rapid increase in cytoplasmic free Ca<SUP>2+</SUP> in pathogenic Leishmania donovani promastigotes

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