ION TRANSPORT AND VOLUME REGULATION IN ASTROCYTES

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Our objectives are to study the basic ion transport processes involved in th swelling of mammalian brain astrocytes, using characterized primary astrocyte monolayer cultures from neonatal rat brains. We will study the cells' responses to exposure to hypo- and hypertonic medium to characterize the ion transport processes involved in volume control. We will also study the effects of possible endogenous effectors of astrocytic swelling under isosmotic conditions, such as lactic acid, L-glutamate, norepinephrine and raised [K+]o, on ion transport, cell volume and intracellular pH. We will use different radioactive tracers to measure ion transport, cell volume and intracellular pH in the attached monolayer cultures. We will use standard electrophysiology to monitor membrane potential and resistance changes, and chloride ion specific microelectrodes to directly study rapid changes in the intracellular activity of this ion. Using detached cells we will follow light scattering to look at rapid volume changes and different fluorescent probes to study membrane potential, intracellular pH and [Ca2+]i under comparable conditions, using a flow cytofluorometer. Astrocytes comprise 20-30% of the mammalian central nervous system (CNS). Classically they were relegated to the role of nerve glue or "neuroglia" and even after their cellular identity was established around the turn of the century they were still considered to be analogous to connective tissue with unspecified supportive roles for neurons. It has become clear that their properties are extremely complex, and their ion transport properties appear to be particularly important for their function. The studies should advance our knowledge in this area and add to an understanding of the role(s) in the mammalian brain of these little-studied cells.