Divalent
cation movement characterizes the final common pathway of cellular death from ischemic or metabolic injury. The influx of
calcium is an essential step in cellular death. We hypothesized that intracellular
magnesium levels may change during the progression to cellular death.
Verapamil-sensitive changes in free ionized intracellular Mg2+ ([Mg2+[i) and Ca2+ ([Ca2+]i) levels were estimated in transformed T-lymphocytes exposed to metabolic inhibitors. Separate experiments used a Mg(2+)-sensitive fluoroprobe,
fura-2 (Ex 1,344, Ex 2,376, Em 500), and a Ca(2+)-sensitive fluoroprobe,
fura-2 (Ex 1,340, Ex 2,380, Em 510). Chemical
anoxia (
sodium cyanide 1 mM,
iodoacetic acid 10 mM) caused a gradual increase in [Ca2+]i (control 126 +/- 13 nM) to > 1 mM by 10 min. This increase in [Ca2+]i was not affected by
verapamil treatment. In separate experiments, [Mg2+]i levels were monitored during chemical
anoxia. The specificity of mag-fura for Mg2+ over Ca2+ was reflected in the absence of a response to the lymphocyte Ca2+ mobilizer OKT-3. Uncorrected control [Mg2+]i levels (.4 +/- .1 mM) were not affected by the combined
cyanide-iodoacetate treatment. A small increase in
mag-fura-2 fluorescence was noted, probably due to binding of Ca2+ to the fluoroprobe when [Ca2]i exceeded 1 mM. Elimination of Ca2+ from the extracellular
buffer increased the resting estimate of intracellular [Mg2+] to 1.6 + .1 mM. These results indicate that 1) extracellular Ca2+ can interfere with the fluorescent determination of intracellular
magnesium concentration, and 2) intracellular free Mg2+ concentrations do not change in this cell line during chemical
anoxia.