CORRELATION OF APOPTOSIS WITH CHANGE IN INTRACELLULAR LABILE ZN(II) USING ZINQUIN ETHYL-8-P-TOLUENESULPHONAMIDO-6-QUINOLYLOXY)ACETIC ACID],A NEW SPECIFIC FLUORESCENT-PROBE FOR ZN(II)

thyl-8-p-toluenesulphonamido-6-quinolyloxy)-acetic acid], a membrane-p ermeant fluorophore specific for Zn(II), was used with spectrofluorime try and video image analysis to reveal and quantify labile intracellul ar Zn. Zinquin labelled human chronic-lymphocytic-leukaemia lymphocyte s, rat splenocytes and thymocytes with a weak diffuse fluorescence tha t was quenched when intracellular Zn was chelated with NNN'N-tetrakis- (2-pyridylmethyl)ethylenediamine (TPEN) and was greatly intensified by pretreatment of cells with the Zn ionophore pyrithione and exogenous Zn. There was substantial heterogeneity of labile Zn among ionophore-t reated cells, and fluorescence was largely extranuclear. The average c ontents of labile Zn in human leukaemic lymphocytes, rat splenocytes a nd rat thymocytes were approx. 20, 31 and 14 pmol/10(6) cells respecti vely. Morphological changes and internucleosomal DNA fragmentation ind icated substantial apoptosis in these cells when the level of intracel lular labile Zn was decreased by treatment with TPEN. Conversely, incr easing labile Zn by pretreatment with Zn plus pyrithione suppressed bo th spontaneous DNA fragmentation and that induced by the potent apopto sis-induced agents colchicine and dexamethasone. These results suggest that prevention of apoptosis is a function of labile Zn, and that a r eduction below a threshold concentration in this Zn pool induces apopt osis.