FRUCTOSE-1,6-BISPHOSPHATE STABILIZES BRAIN INTRACELLULAR CALCIUM DURING HYPOXIA IN RATS

Background and Purpose: Exogenously administered fructose-1,6-bisphosphate reduces neuronal injury from hypoxic or ischemic brain insults. To test the hypothesis that fructose-1,6-bisphosphate prevents changes in intracellular calcium ([Ca2+]i) and high-energy phosphate levels, we measured [Ca2+]i, intracellular pH (pH(i)), and adenosine triphosphate in cultured rat cortical astrocytes and cortical brain slices during hypoxia. Methods: The fluorescent indicators fura-2 and bis-carboxyethyl-carboxyfluorescein were used to simultaneously measure [Ca2+]i and pH(i) with a fluorometer. Results: Exposure to hypoxia (95% N2, 5% CO2) or 100 muM sodium cyanide produced transient increases in [Ca2+]i in astrocytes and sustained increases in [Ca2+]i in brain slices. Adenosine triphosphate levels fell in slices exposed to hypoxia or cyanide. Fructose-1,6-bisphosphate (3.5 mM) blocked increases in [Ca2+]i and prevented depletion of adenosine triphosphate. Fructose-1,6-bisphosphate also partially prevented adenosine triphosphate depletion in brain slices incubated in glucose-free medium. Iodoacetate (a specific inhibitor of glycolysis) elevated [Ca2+]i and partially prevented these actions of fructose-1,6-bisphosphate. Changes in pH(i) during hypoxia were not affected by fructose-1,6-bisphosphate. Conclusions: Fructose-1,6-bisphosphate supports adenosine triphosphate production via stimulation of glycolysis and results in the maintenance of normal [Ca2+]i during hypoxia or hypoglycemia.