Effect of calcium antagonists, calcium channel blockers and calmodulin inhibitors on the growth and encystation of Entamoeba histolytica and E-invadens

The effects of calcium antagonists, calcium channel blockers, and calmoduli n inhibitors on the growth of Entamoeba histolytica and the growth and ency station of Entamoeba invadens were examined. Calcium chelators ethyleneglyc ol bis (beta -aminoethyl ether)-N,N ' -tetraacetate (EGTA) and ethylenediam inetetraacetate (EDTA) inhibited the growth of both Entamoeba and also the encystation of E. invadens in a dose-dependent manner, with EDTA being more effective than EGTA. A putative antagonist of intracellular calcium flux, 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate (TMB-8) also inhibited both growth and encystation, with the E. histolytica being more sensitive t han E. invadens, and with the growth of E. invadens being more sensitive th an encystation. The slow Na+-Ca2+ channel blockers bepridil and verapamil i nhibited both growth and encystation. Bepridil was more effective than vera pamil. The calmodulin (CaM) inhibitors, W-7 (N-(6-aminohexyl)-chloro-1-naph talene sulphonamide) and trifluoperazine (TFP), were also inhibitory for bo th the growth and encystation; TFP was more effective than W-7, and encysta tion was more sensitive than growth in E. invadens. These results indicate that extracellular calcium ions, amebic intracellular calcium flux, calcium channels, and a CaM-dependent process contribute to the growth and encysta tion of Entamoeba.