Autoradiographic quantitation of beta-adrenergic receptors on neural cells in primary cultures. I. Pharmacological studies of [125I] pindolol binding of individual astroglial cells.

As part of an investigation into the expression of neurotransmitter receptors on astroglia, we have developed a method to label beta-adrenergic receptors on immunocytochemically stained cultured cells using autoradiography of 125I-labelled beta-adrenergic receptor ligands. The current investigation was undertaken to determine whether the binding of [125I]pindolol (*IPIN) to immunocytochemically stained cultured cells, as measured by quantitative autoradiography, would fulfill the usual pharmacological criteria for specific beta-adrenergic receptor binding. *IPIN binding experiments were carried out on individual astroglia obtained from neonatal rat cerebral cortex and grown as primary cultures on polylysine-coated glass slides. Autoradiographic silver grains on cells which stained for the intracellular astroglial marker, glial fibrillary acidic protein (GFAP), were quantified by a microcomputer-based video digitizing system. We determined that competition for *IPIN binding by propranolol and isoproterenol was stereospecific, that specific binding of *IPIN was saturable, and that *IPIN binding sites were lost after isoproterenol-induced desensitization. These results provide convincing evidence that we can quantitatively examine beta-adrenergic receptors on single cells. The use of computerized video methods greatly facilitates the rapid quantitation of autoradiographic grains associated with immunocytochemically identified cells. This study is a unique demonstration of receptor binding parameters derived from single cells in a known population, and represents a novel approach to the problem of assessing cell-type specific receptors on neural cells in mixed primary cultures.