Albumin elicits calcium signals from astrocytes in brain slices from neonatal rat cortex.

1. Albumin causes calcium signals and mitosis in cultured astrocytes, but it has not been established whether astrocytes in intact brain also respond to albumin. The effect of albumin on intracellular calcium concentration ([Ca2+]i) in single cells was therefore studied in acutely isolated cortical brain slices from the neonatal rat. 2. Physiological concentrations of albumin from plasma and from serum produced an increase in [Ca2+]i in a subpopulation of cortical cells. Trains of transient elevations in [Ca2+]i (Ca2+ spikes) were seen in 41 % of these cells. 3. The cells responding to albumin are identified as astrocytes because the neurone-specific agonist NMDA caused much smaller and slower responses in these cells. On the other hand NMDA-responsive cells, which are probably neurones, exhibited only small and slow responses to albumin. The residual responses of astrocytes to NMDA and neurones to albumin are likely to be due to crosstalk with adjacent neurones and astrocytes, respectively. 4. Methanol extraction of albumin removes a polar lipid and abolishes the ability of albumin to increase intracellular calcium. 5. Astrocyte calcium signalling caused by albumin may have important physiological consequences when the blood-brain barrier breaks down and allows albumin to enter the CNS.