No abstract

Recent evidence suggests that intracellular Zn 2؉ accumulation contributes to the neuronal injury that occurs in epilepsy or ischemia in certain brain regions, including hippocampus, amygdala, and cortex. Although most attention has been given to the vesicular Zn 2؉ that is released into the synaptic space and may gain entry to postsynaptic neurons, recent studies have highlighted pools of intracellular Zn 2؉ that are mobilized in response to stimulation. One such Zn 2؉ pool is likely bound to cytosolic proteins, like metallothioneins. Applying imaging techniques to cultured cortical neurons, this study provides novel evidence for the presence of a mitochondrial pool distinct from the cytosolic protein or ligand-bound pool. These pools can be pharmacologically mobilized largely independently of each other, with Zn 2؉ release from one resulting in apparent net Zn 2؉ transfer to the other. Further studies found evidence for complex and potent effects of Zn 2؉ on isolated brain mitochondria. Submicromolar levels, comparable to those that might occur on strong mobilization of intracellular compartments, induced membrane depolarization (loss of ⌬ m), increases in currents across the mitochondrial inner membrane as detected by direct patch clamp recording of mitoplasts, increased O2 consumption and decreased reactive oxygen species (ROS) generation, whereas higher levels decreased O2 consumption and increased ROS generation. Finally, strong mobilization of proteinbound Zn 2؉ appeared to induce partial loss of ⌬ m, suggesting that movement of Zn 2؉ between cytosolic and mitochondrial pools might be of functional significance in intact neurons.

Several novel fluorinated fluoresceins (Oregon Green dyes) were prepared by the reaction of fluororesorcinols with phthalic anhydride and its derivatives. A novel regiospecific synthesis of fluororesorcinols was key to the successful synthesis of these new fluorophores. (Polyfluoro)nitrobenzenes were reacted with 2 equiv of sodium methoxide followed by reduction, hydrodediazoniation, and demethylation, giving the first straightforward synthesis of 2-fluororesorcinol, 4-fluororesorcinol, 2,4-difluororesorcinol, and 2,4,5-trifluororesorcinol. These fluorinated fluoresceins have higher photostability and ionize at a lower pH (pK a = 3.3−6.1) than fluorescein (pK a = 6.5). Some of the fluorinated fluoresceins have very high quantum yields (0.85−0.97), which, in combination with their lower pK as and high photostability, makes them superior fluorescent dyes for use as reporter molecules in biological systems.