Astroglial cells in vitro are heterogeneous with respect to expression of the alpha 1-adrenergic receptor.

A wide variety of approaches have been used to examine the expression of neuroligand receptors by cultured astroglial cells. The results of such studies make it clear that these cells exhibit most, if not all, of the different receptors known to be associated with central neurons. However, it has been more difficult to determine if there are multiple populations of astroglia that can be distinguished on the basis of their complement of neuroligand receptors. To address this question, we established a radioligand binding assay that enabled us to visualize alpha 1-adrenergic receptors (alpha 1-ARs) on immunocytochemically defined neural cells. Saturation, time course, and competition binding experiments determined that 125I-HEAT could be used to identify alpha 1-AR binding sites on immunocytochemically defined astroglial cells. Our results indicate that approximately 66% of cortical polygonal astroglia express detectable numbers of alpha 1-ARs. 3H-thymidine labeling experiments indicate that both dividing and nondividing astroglia exhibit alpha 1-ARs. These results greatly contrast with studies on beta-adrenergic receptor expression (beta-AR), in which 100% of polygonal astroglia express beta-ARs. Process-bearing astroglia also exhibit alpha 1-ARs, which is in marked contrast to the lack of beta-AR expression by these cells. The results presented here suggest that astroglia, like neurons, differ in the receptors they express and therefore may be able to selectively respond to extracellular stimulation.