Ca2+ signaling in the transformation of promastigotes to axenic amastigotes of Leishmania donovani

The present study is an attempt to look into the role of Ca2+ in signaling the transformation of promastigotes to axenic amastigotes. An estimation of intracellular free calcium concentration at 6 h intervals during the conve rsion of promastigotes to axenic amastigotes (72 h) revealed a 10 fold incr ease in [Ca2+](i) at the initial 6-12 h during the conversion. This was fol lowed by declining levels till 60 h and the concentration thereafter remain ed constant. Axenic amastigotes (72 h) had a 5 fold higher [Ca2+](i) as com pared to the promastigotes. A 30-40% decrease in [Ca2+](i) after pretreatme nt of cells with dentrolene and a gradual rise of intracellular Ca2+ in [Ca 2+] free medium indicates the role of intracellular calcium pools in the el evation of [Ca2+](i). A sudden increase in [Ca2+](i) on addition of NH4Cl ( 20 mM) in the cells grown in Ca2+ free medium indicates the presence of aci docalcisomes, as intracellular Ca2+ storing pool, in L. donovani. To study the role of Ca2+ influx from the external medium in the morphogenetic trans formation and in the elevation of [Ca2+](i) a Ca-45(2+) uptake study was pe rformed. Maximum uptake of Ca-45(2+) was observed in the initial 24 h of tr ansformation and maximum Ca2+ ATPase activity was also observed between 24- 42 h. So the presence of low Ca2+ in the cytosol, existence of intracellula r Ca2+ pools and presence of mechanisms to maintain the Ca2+ homeostasis in the cells suggests that Ca2+ can be an appropriate candidate for a second messenger during the morphogenetic transformation of L. donovani.