Journal Cover: 2002

rSlo KCa Channels in Glial Cells are Highly Localized to Astrocytes Associated With the Brain Vasculature

Evidence that Ca2+-activated K+ (KCa) channels play a role in cell volume changes and K+ homeostasis led to a prediction that astrocytes would have KCa channels near blood vessels in order to maintain K+ homeostasis. Consistent with this thinking, the present study demonstrates that rSlo KCa channels are in glial cells of the adult rat CNS and highly localized to specializations of astrocytes associated with the brain vasculature. Using confocal and thin-section electron microscopic immunolabeling methods the distribution of rSlo was examined in adult rat brain. Strong rSlo immunolabeling was present around the vasculature of most brain regions. Examination of dye-filled hippocampal astrocytes revealed rSlo immunolabeling polarized at astrocytic endfeet. Ultrastructural analysis confirmed that the rSlo staining was concentrated in astrocytic endfeet ensheathing capillaries as well as abutting the pia mater. Immunostaining within the endfeet was predominantly distributed at the plasma membrane directly adjacent to either the vascular basal lamina or the pial surface. The distribution of the aquaporin-4 (AQP-4) water channel was also examined using dye-filled hippocampal astrocytes. In confirmation of earlier reports, intense AQP-4 immunolabeling was generally observed at the perimeter of blood vessels, and coincided with perivascular endfeet and rSlo labeling. We propose that rSlo KCa channels, with their sensitivity to membrane depolarization and intracellular calcium, play a role in the K+ modulation of cerebral blood flow. Additional knowledge of the molecular and cellular machinery present at perivascular endfeet may provide insight into the structural and functional molecular elements responsible for the neuronal activity-dependent regulation of cerebral blood flow.

Price DL, Ludwig JW, Mi H, Schwarz TL, Ellisman MH (2002) Distribution of rSlo Ca2+-Activated K+ Channels in Rat Astrocyte Perivascular Endfeet. Brain Research 956: 183-193. PubMed