THE CALCIUM CONTENT OF MITOCHONDRIA FROM BRAIN SUBREGIONS FOLLOWING SHORT-TERM FOREBRAIN ISCHEMIA AND RECIRCULATION IN THE RAT

A procedure was established for determining the calcium content of mit ochondria isolated from rat brain subregions based on changes in fura- 2 fluorescence after disruption of the organelles with Triton X-100 an d sodium dodecyl sulfate. Mitochondria isolated from the forebrain of normal rats contained 2.5 +/- 0.9 nmol of calcium/mg of protein. A 30- min ischemic period produced an approximately twofold increase in the calcium content of mitochondria isolated from the dorsolateral striatu m, a region in which most neurons die within 24 h after this period of ischemia. The calcium content of mitochondria from the paramedian cor tex, a region in which there are few ischemia-susceptible neurons, ten ded to be similarly increased, although this difference was not statis tically significant. Larger increases (to approximately five times con trol values) were seen in mitochondria isolated from both regions afte r 10 min of recirculation. By 1 h of recirculation, mitochondrial calc ium had returned close to preischemic control values in both regions. Longer recirculation periods produced no further changes in the calciu m content of mitochondria from the paramedian cortex. However, mitocho ndrial calcium was again increased in the dorsolateral striatum after 6 h (6.5 nmol of calcium/mg of protein) and 24 h (8.7 nmol of calcium/ mg of protein) of recirculation. This regionally selective increase in calcium in the dorsolateral striatum preceded the period during which the majority of neurons in this region exhibit advanced degenerative changes. Thus, this increase may be an essential step, albeit a late o ne, in the development of neuronal loss.