calcimycin and Leishmaniasis--Visceral

Lipophosphoglycan (LPG), a major surface molecule from Leishmania donovani, stimulated ornithine decarboxylase (ODC) activity in macrophages in a dose- and time-dependent manner. LPG stimulated the rapid increase in ODC activity within 30 min after exposure, suggesting that the interaction of LPG with its receptor stimulated a specific signal transduction pathway. However, LPG-induced ODC activity was a transient event because 3 hr after exposure to LPG, no stimulation of ODC activity was detectable. ODC activity appeared to be coupled to the activation of protein kinase C (PKC) in macrophages, as activators of PKC caused a rapid increase in the ODC activity. Macrophages pretreated with LPG for 1 hr became unresponsive to subsequent stimulation by the PKC activators 1-oleoyl-2-acetyl-glycerol and the calcium ionophore A23187. In contrast, the ability of macrophages to express ODC activity in response to the cyclic AMP analogue dibutyryl cyclic AMP was not impaired by LPG.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Anti-Bacterial Agents; Bucladesine; Calcimycin; Diglycerides; Dose-Response Relationship, Drug; Enzyme Activation; Enzyme Inhibitors; Glycosphingolipids; Leishmania donovani; Leishmaniasis, Visceral; Lipopolysaccharides; Macrophages; Mice; Okadaic Acid; Ornithine Decarboxylase; Signal Transduction; Staurosporine; Tetradecanoylphorbol Acetate; Time Factors

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.

Topics: Animals; Calcimycin; Calcium; Cytoplasm; Humans; Kinetics; Leishmania donovani; Leishmaniasis, Visceral; Manganese; Mitochondria; Nigericin; Oligomycins; Sodium Cyanide; Species Specificity; Spectrometry, Fluorescence; Temperature; Virulence