Fluorometric Measurement of Intracellular pH in vivo in Feline Cerebral Cortex during Ischemia and Reperfusion

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Intracellular acidosis has been considered to play a pivotal role in the progression of neu-ronal damage after cerebral ischemia. However, continuous measurement of the intracellular potential of hydrogen (pH) has not been done during and after ischemia. We measured temporal changes in intracellular pH in the feline cerebral cortex in vivo during and after ischemia using a novel fluorescent pH probe, 2', 7'-biscarboxyethyl carboxyfluorescein (BCECF). A closed cranial window was installed in the left temporal skull. BCECF acetoxymethyl ester was superfused over the cortex, hydrolyzed and trapped in cortical cells. Intracellular pH was measured utilizing excitation light at 507nm and fluo-rescent light at 550.5nm. Focal cerebral ischemia for 60 minutes was induced by means of middle cere-bral artery occlusion. Intracellular pH in the severely ischemic group became significantly acidic (p<0.01) during ischemia and the acidosis persisted for at least 30 minutes after recirculation. The pH change was not significant in the mildly ischemic group. The severity of ischemia was determined based on the mean transit time, which was calculated from the hemodilution curve obtained by bolus injec-tion of saline. The extent of ischemia was further confirmed pathologically (p<0.01). The above results suggest that intracellular acidosis resulting from severe ischemia persists even after recircula-tion.