Figure 7.

Increase in EDNRB-specific binding sites in the light-damaged retina. A, Binding of ¹²⁵I-EDN1 to fresh-frozen eye sections from control BALB/c mice maintained in darkness (left member of each pair of eyes) or BALB/c mice exposed to bright light for 6 h with pupil dilation, followed by 24 h of recovery in darkness (right member of each pair of eyes). Binding was performed in either the absence of competitor or the presence of 1 μm of the indicated competitor. The ¹²⁵I signal is shown in the top row of panels, and the toluidine blue staining pattern is shown in the bottom row. Light exposure produces a large increase in ¹²⁵I-EDN1 binding, almost all of which is blocked by BQ788 (an EDNRB antagonist) and unaffected by BQ123 (an EDNRA antagonist) and is therefore referable to EDNRB. B, Binding of ¹²⁵I-EDN1 to retinal membranes from BALB/c mice exposed to bright light for 3 h with pupil dilation, followed by 24 h of recovery in darkness (left 4 bars), or from control BALB/c mice maintained in darkness (right 4 bars). Binding was performed in either the absence of competitor or the presence of 1 μm of the indicated competitor. The histogram shows the means and SDs for three independent experiments. In the dark-adapted retina, ∼70% of endothelin binding sites are EDNRB. With light damage, the number of EDNRB sites increases ∼12-fold; the number of EDNRA sites shows little change.