In contrast to mammalian brain, which exhibits rapid degeneration during
anoxia, the brains of certain species of turtles show an extraordinary capacity to survive prolonged
anoxia. The decrease in energy expenditure shown by the anoxic turtle brain is likely to be a key factor for anoxic survival. The "channel arrest" hypothesis proposes that
ion channels, which regulate brain electrical activity in normoxia, may be altered during
anoxia in the turtle brain as a mechanism to spare energy. Goals of present research were to test this hypothesis and to determine whether down-regulation of
sodium channels is a possible explanation for spike threshold shifts seen during
anoxia in isolated turtle cerebellum. We report here that
anoxia induced a significant (42%) decline in
voltage-gated sodium channel density as determined by studies of the binding of a
sodium channel ligand, [3H]
brevetoxin. This study demonstrates that
sodium channel densities in brain may be regulated by tissue oxygenation or by physiological events associated with
anoxia. Moreover, it also suggests that downregulation of
sodium channels may be a basis for changes in action potential thresholds, the electrical depression and energy conservation that provide the unique anoxic tolerance of turtle brain.