LOCALIZATION AND CHARACTERIZATION OF EPIDERMAL GROWTH-FACTOR RECEPTORS IN THE DEVELOPING RAT MEDIAL SEPTAL AREA IN CULTURE

The presence and binding properties of epidermal growth-factor recepto rs (EGF-Rs) in different cell types purified from the rat medial septa l area in culture were investigated. We report that astrocytes, oligod endrocytes and neurons from this area possess EGF-Rs while microglia d o not. EGF-binding sites are detectable on astrocytes derived from the medial septum of both embryonic and neonatal rats. Scatchard analysis of the data for astrocytes from the fetal rats show that EGF specific ally binds to both high- (K-d = 7.21 x 10(-10) M, B-max = 3602 recepto rs/cell) and low-affinity (K-d = 3.99 X 10(-8) M, B-max = 86,265 max r eceptors/cell) receptors on these cells. On the other hand, astrocytes purified from neonatal tissue possess a greater number of high-affini ty receptors (B-max = 10,938 receptors/cell) when compared with the em bryonic astroglia. With time in culture, the number of both types of r eceptors on neonatal astrocytes decreases. Oligodendrocytes also posse ss high- and low-affinity EGF-Rs with dissociation constants of 3.25 x 10(-10) M and 3.85 x 10(-8) M, respectively. The number of receptors on oligodendrocytes is significantly lower than those on neonatal astr ocytes (B-max = 1185 and 25,081 receptors/cell for high- and low-affin ity binding sites, respectively). Finally, neurons from this area also exhibit two different EGF-R types with dissociation constants similar to those described for astrocytes. As the number of receptors/neuron (B-max = 136 and 1159 receptors/cell for high- and low-affinity bindin g sites, respectively) appears to be extremely low, it is possible tha t EGF specifically binds only to a subpopulation of neurons from this area. These studies demonstrate which cell types in the developing med ial septal area possess EGF-Rs and provide a detailed characterization of these binding sites. These EGF-R-bearing cells may be potential ta rgets for this growth factor or for transforming growth factor ct in t his brain area.