K+ homeostasis in the brain: a new role for glycogenolysis.

The results of the study of Xu and colleagues in this issue constitute a critical new piece of information on the functional specialization of astrocytes for K(+) homeostasis in the brain. The relationship between astrocytes and potassium has been long recognized in half a century of research. Now this relation appears to have found its metabolic correlate in astrocytic glycogen. Xu et al. showed that glycogen is committed to fuel astrocytic K(+) uptake, as this process is abolished when glycogenolysis is inhibited even in the presence of glucose. They went further by showing that the cellular mechanisms which selectively mobilize glycogen involve the participation of several intracellular signaling cascades. As with all good science, these findings generate a number of fundamental questions that are open for experimental research.