β-Adrenergic receptors of cerebellar astrocytes in culture: intact cells versus membrane preparation

Experiments were carried out to assess: (i) the influence of culture conditions on the expression of β-adrenergic receptors in intact glial cells from the central nervous system; and (ii) the extent to which quantitation of receptor sites in membrane preparations reflects the receptor population of the whole cells they are derived from. Cerebellar astrocytes were chosen for this study since essentially one receptor subtype, the β 2 one, is present in adult cerebellum. Intact, attached cerebellar astrocytes exhibit only one class of binding sites for the β-adrenergic antagonist, [ 3H]CGP 12177. Replating of the astrocytes after a few days of culture in vitro induces an up-regulation of the receptors. This effect is particularly important when astrocytes are maintained for 6 days in the presence of horse serum, a condition that favors cellular differentiation. Only 30–50% of the β-adrenergic receptors of the intact cells can be detected on membrane preparations. When membranes are prepared from astrocytes grown either in the presence of horse serum or under chemically controlled medium (i.e. under differentiation promoting conditions) two classes of binding sites for [ 125I](−)-iodocyanopindolol are revealed. Several hypotheses, mainly related to the morphology of the cells, may provide an explanation for such differences. Studies of the pharmacological specificity of receptors of membrane fractions show that cerebellar astrocytes cultured in vitro exhibit both β 1 and under which they exhibit a polygonal, poorly differentiated morphology. When culture conditions favor cellular differentiation, more receptors of the β 2 subtype are seen, which can be related to what is observed in the adult in vivo where the astrocytes exhibit a differentiated morphology.