CAN THE INDO-1 FLUORESCENCE APPROACH MEASURE BRAIN INTRACELLULAR CALCIUM IN-VIVO - A MULTIPARAMETRIC STUDY OF CEREBROCORTICAL ANOXIA AND ISCHEMIA

Indo-1 fluorescence was used to monitor intracellular calcium levels i n the cat brain in vivo, using the approach proposed by Uematsu et al. [Uematsu D., Greenberg J.H., Reivich M., Karp A. In vivo measurement of cytosolic free calcium during cerebral ischemia and reperfusion. An n Neurol 1988; 24: 420-428]. In addition, extracellular calcium and po tassium levels, NADH redox state, electrocorticogram (ECoG), DC potent ial and relative cerebral blood flow were monitored simultaneously. Ch anges in the Indo-1 fluorescence ratio F-400/F-506 were monitored duri ng anoxia, reversible ischemia and irreversible ischemia. Although the se perturbations resulted in the expected changes in extracellular cal cium and potassium levels, NADH redox state, ECoG and other physiologi cal parameters, they did not result in significant increases in the F- 400/F-506 ratio. The apparent insensitivity of the in vivo Indo-1 appr oach is due to the difficulty in obtaining accurate fluorescence signa ls from Indo-1 in the brain. Two reasons for this difficulty appear to be problems in loading Indo-1 into the brain, and problems in correct ing Indo-1 fluorescence signals for changes in NADH fluorescence and c hanges in absorption of intrinsic chromophores. Under the conditions o f our in vivo cat experiments, Indo-1 fluorescence is not a viable app roach for measuring changes in cerebral intracellular calcium levels.