INOSITOL(1,3,4,5) TETRAKISPHOSPHATE PLAYS AN IMPORTANT ROLE IN CALCIUM MOBILIZATION FROM ENTAMOEBA-HISTOLYTICA

Calcium release from internal stores of Entamoeba histolytica, a paras itic protozoan, was observed by measuring fluorescence of Fura-2. Empt ying of inositol(1,4,5)trisphosphate (Ins(1,4,5)P-3)-sensitive calcium pools in permeabilized E. histolytica did not significantly affect su bsequent calcium release by inositol(1,3,4,5)tetrakis-phosphate (Ins(1 ,3,4,5)P-4). Similarly, prior depletion of Ins(1,3,4,5)P-4-sensitive s tores did not have any influence on subsequent calcium release by Ins( 1,4,5)P-3. The EC(50) for calcium release was 0.15 mu M with Ins(1,4,5 )P, and 0.68 mu M with Ins(1,3,4,5)P-4. In conclusion, the Ins(1,3,4,5 )P-4-sensitive calcium store in E. histolytica is separate and indepen dent from the Zns(1,4,5)P-3-sensitive pool.