HUMAN Y-79 RETINOBLASTOMA CELLS EXHIBIT SPECIFIC CORTICOTROPIN-RELEASING HORMONE-BINDING SITES

In this study we have identified specific binding sites for corticotro pin-releasing hormone (CRH) in human Y-79 retinoblastoma cell membrane s by using I-125-Tyr-ovine CRH ((125)l-oCRH) as radioligand. Binding a t 19 degrees C was rapid with steady state being reached within 20 min , reversible and linear with membrane protein concentration. The (125) l-oCRH binding was enhanced by Mg2+ and inhibited by the GTP analogue guanosine 5'-O-(3'-thiotriphosphate). Y-79 cell membranes exhibited tw o populations of binding sites, a high-affinity site with an apparent dissociation constant (K-D) of 1 nM and a low-affinity site with an ap parent K-D of 500 nM. (125)l-oCRH binding was completely antagonized b y human/rat CRH, [Met(O)(21)]oCRH, alpha-helical CRH(9-14), urotensin l, and sauvagine with a rank order of potency similar to that displaye d by CRH receptors of other tissues. These data describe for the first time the presence of specific CRH-binding sites in retinal cells. The Y-79 cell line may therefore constitute a valuable model in which to study CRH action on retinal cells.