Astrocyte beta(1)-adrenergic receptor immunoreactivity and agonist inducedincreases in [Ca2+](i) - Differential results indicative of a modified membrane receptor

Antibodies against the C-terminus of the beta(1)-adrenergic receptor were u sed for staining cultured astrocytes from the rat cerebral cortex. Immunore activity was found to be localized exclusively to an intracellular organell e structure similar to the Golgi complex, with no staining of the plasma me mbrane. The astrocytes stained positive with BODIPY CGP 12177, a FITC-conju gated beta-adrenergic receptor agonist, and this staining was blocked by th e beta(1)-adrenergic antagonist atenolol, indicating that these receptors a re expressed on the surface of the astrocytes. The presence of functional p lasma membrane beta(1)-adrenergic receptors was further verified using micr ospectrofluorometry for measurements of intracellular calcium changes upon beta-adrenergic agonist stimulation. Intracellular immunoreactivity confine d to the organelles was also found in astrocytes from mixed astroglial-neur onal cultures. In contrast, the neurons in these cultures showed a strong l abeling of the cell bodies by the beta(1)-adrenergic receptor antibodies. T hus, the beta(1)-adrenergic receptor antibody, which stains the cell bodies of the neurons, recognizes the astroglial receptors only intracellularly, although functional beta(1)-adrenergic receptors are present on the astrogl ial surface. Taken together, these data suggest that the beta(1)-adrenergic receptors observed intracellularly might be processed on their passage to the surface to a modified form of the final plasma membrane receptor, which is not recognized by the antibodies. (C) 2000 Elsevier Science Inc. All ri ghts reserved.