Developmental changes in endothelin A and endothelin B receptor subtypes in embryonic chick brains

The kD and Bmax values for [125I]endothelin-1 ([125I]ET-1) binding to the brain membrane preparations of 3- to 20-day-old chick embryos were compared. The kD values differed only slightly during development. In contrast, the Bmax values varied six-fold during the embryonic stages examined and displayed two distinct peaks, on day 5 (204 +/- 13 fmol/mg protein, n = 3) and day 13 (110 +/- 4 fmol/mg protein, n = 7) of incubation. Displacement of [125I]ET-1 binding to 5- and 13-day-old embryonic brain membrane preparations was carried out using ET-3 and BQ-123, a selective ETA receptor antagonist, as competing ligands. The results suggest that the ETA receptor subtype is primarily synthesized at the beginning of development followed by the production of non-selective ETB receptor subtype at a later time.