Inositol 1,4,5-triphosphate induces calcium release from a non- mitochondrial pool in amoebae of Dictyostelium.

Evidence is presented for two distinct CA2+ pools in amoebae of Dictyostelium discoideum. One pool, presumably mitochondrial, was sensitive to the mitochondrial inhibitors oligomycin and dinitrophenol and showed an affinity for Ca2+ in the micro M concentration range. The other Ca2+ pool, which was insensitive to these inhibitors, was of lower capacity but had higher affinity (in the nM range). Inositol 1,4,5-trisphosphate (5 micro M) added to saponin-permeabilized amoebae induced a rapid release of Ca2+ from the latter pool but had no effect on the presumed mitochondrial pool. Controls using addition of inositol 1,4-bisphosphate (the hydrolytic product of IP3) induced no such CA2+ release. The results provide strong support for the involvement of IP3 in signal transmission during chemotaxis of D. discoideum.