title: Effect of intracellular acidity and ionomycin on apoptosis in HL-60 cells.
abstract: The aim was to investigate in detail the influence of intracellular pH (pHi) and intracellular Ca2+ concentration ([Ca2+]i) on apoptosis in HL-60 human promyelocytic leukaemia cells. The pHi was controlled by changing the pH of media as well as by interfering with the pHi regulatory mechanisms with 3-amino-6-chloro-5-(1-homopiperidyl)-N-(diaminomethylene) pyrazincarboxamide (HMA; an inhibitor of Na+/H+ antiport), 4-diiosothiocyanatostilbene-2,2'disulfonic acid, (DIDS; an inhibitor of Na(+)-dependent HCO3-/Cl- exchange) and nigericin (a K+ ionophore). The [Ca2+]i was increased with ionomycin, a Ca2+ ionophore. The apoptosis of HL-60 cells was measured with conventional agarose gel electrophoresis for DNA fragmentation and also with the release of 3H from 3H-thymidine-labelled DNA. Based on the magnitude of DNA fragmentation and 3H release at different pHi, it was shown that apoptosis occurred in HL-60 cells when the pHi was lowered from normal pHi of 7.4 to about 7.2-6.7 with a peak increase at pHi 6.8-6.9. Addition of 4 microM ionomycin to RPMI 1640 medium, which contained 615 microM Ca2+, elevated the apoptosis in the cells. Such an increase in apoptosis by ionomycin in HL-60 cells appeared to result from both an increase in [Ca2+]i and from a decline in pHi. The results indicate that the acidic intratumour environment may greatly affect the response of neoplastic tissues to hyperthermia, radiation and chemotherapeutic drugs which cause apoptosis.
authors.affiliation: Department of Microbiology, Inha University, Inchon, Korea.
authors.forename: H J
authors.initials: HJ
authors.lastname: Park
authors.forename: C M
authors.initials: CM
authors.lastname: Makepeace
authors.forename: J C
authors.initials: JC
authors.lastname: Lyons
authors.forename: C W
authors.initials: CW
authors.lastname: Song
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002118:Calcium / Q000032:analysis*; D004249:DNA Damage; D018922:HL-60 Cells / Q000737:chemistry / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects*; D015759:Ionomycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology*; D015473:Leukemia, Promyelocytic, Acute / Q000473:pathology*
chemical_list: D007476:Ionophores; D015759:Ionomycin; D002118:Calcium