Effect of 2,6-diisopropylphenol and halogenated anesthetics on tetraphenylphosphonium uptake by rat brain synaptosomes: Determination of membrane potential

The effect of 2,6-diisopropylphenol (propofol) in comparison to that of the halogenated anesthetics enflurane, isoflurane, and halothane on tetrapenylphosphonium uptake by rat brain synaptosomes was studied. A direct method to separately measure the synaptosomal and the mitochondrial transmembrane potential by using the tetraphenylphosphonium cation (TPP+) was utilized. The latter is a lipophylic charged molecule which distributes between two compartments according to the transmembrane electrical potential in the presence or absence of 60 mM KCl as a synaptosomal membrane depolarizing agent. After previously reporting the damages induced by general anesthetics on isolated mitochondria, the aim of this paper was to study their possible action on the synaptosomal membrane potential and whether or not drugs concentrations damaging isolated mitochondria are also effective on synaptosomal mitochondria. The results indicated that, in the presence of glucose, mitochondria included in synaptosomes were able to maintain a transmembrane potential of 202 +/- 8 mV (mean +/- SD) while the synaptosomal membrane showed a potential of 78 +/- 8 mV (mean +/- SD). When anesthetic concentrations (0.6-1 mM propofol, 10-40 mu M enflurane, 30-50 mu M isoflurane, 8-15 mu M halothane) that impair mitochondrial energy metabolism were used, the synaptosomal transmembrane potential was maintained and, in addition, a slight increase of the TPP+ taken up was observed as the anesthetic concentration was increased.