Pharmacologically-distinct subsets of astroglia can be identified by their calcium response to neuroligands

Type 1 astroglia have been reported to exhibit in excess of 20 different neuroligand receptors in vitro. The aim of this study was to determine if astroglia, like neurons, are heterogeneous with respect to their ability to respond to different neuroligand receptor agonists. Type 1 astroglia were loaded with the calcium indicator dye fura-2 and the influence of six different neuroligands on their intracellular calcium levels was examined using a video-based imaging system. Each of the six different neuroligands tested increased calcium levels in a subpopulation of glial fibrillary acidic protein immunopositive cells (astroglia). The percentage of cerebral cortical type 1 astroglia responding to a given neuroligand varied with the agonist and generally followed the order: 2-methylthio-ATP greater than phenylephrine greater than carbachol = serotonin greater than glutamate = histamine. The results also indicate that a single astroglial cell can respond to one agonist with a sustained rise in calcium levels and to an alternate agonist with oscillations in calcium levels. The pharmacological heterogeneity evident among astroglia does not appear to depend on cell proliferation or association with neurons. The results of our studies indicate that cultures of cerebral cortical type 1 astroglia are composed of distinct subsets of cells that can be distinguished by qualitative differences in their ability to respond to specific neuroligands with a rise in intracellular calcium.