Cerebral type 2 astroglia are heterogeneous with respect to their ability to respond to neuroligands linked to calcium mobilization

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Abstract
Very little information is available concerning the pharmacology of type 2 astroglia. During the past decade it has become apparent that two distinct lineages of astroglial cells can be defined in vitro. These two lineages are commonly referred to as type 1 and type 2 and are distinguished from each other on the basis of their morphological features and antigenic phenotypes. In contrast to type 1 astroglia, very little is known about the pharmacology of type 2 astroglia. The lack of information concerning the responsiveness of these cells stems primarily from difficulties encountered in isolating large numbers of type 2 astroglia free of other cell types. In the present study video‐ and photometer‐based imaging systems were used to monitor the influence of a series of neuroligands on the intracellular calcium levels of individual cerebral type 2 astroglia in order to assess their expression of calcium‐mobilizing receptors. The responses of 85 immunocytochemically identified cerebral type 2 astroglia to bradykinin (BK), norepinephrine (NE), histamine (HIST), carbachol (CARB), 2‐methyl‐thio ATP (2MT‐ATP), glutamate (GLUT), and serotonin (5‐HT) were analyzed. Approximately 50% of cerebral type 2 astroglia responded to BK, NE, HIST, CARB, and 2MT‐ATP whereas only 16% and 9% of the cells responded to GLUT and 5‐HT, respectively. The number of neuroligands that increased calcium in individual cells ranged from 0 to 6. These responses are quite similar to those previously demonstrated in cultured cerebral type 1 astroglia. No pattern of receptor co‐expression was observed for the different neuroligands tested. While variable, distinct differences were observed in the time course of the calcium responses elicited by different neuroligands. The present study demonstrates that cultured cerebral type 2 astroglia are heterogenous when judged by their ability to respond to neuroligands with a rise in intracellular calcium.