Binding sites for 125I ET-1, ET-2, ET-3 and vasoactive intestinal contractor are present in adult rat brain and neurone-enriched primary cultures of embryonic brain cells.

Binding sites for iodinated endothelin (ET)-2, ET-3 and vasoactive intestinal contractor (VIC) were visualised in the adult rat brain using quantitative autoradiography and have a similar anatomical distribution to that of ET-1 and sarafotoxin S6b. Highest densities of binding sites for all 5 labelled peptides were present in the granular layer of the cerebellum. Cross-competition experiments show that at a concentration of 1 microM, unlabelled ET-1, ET-2, ET-3, VIC and sarafotoxin S6b were able to compete for the binding sites detected by each of the iodinated peptides. Binding sites for the ET isoforms were also present after 7-14 days in vitro in neurone-enriched primary cultures derived from embryonic rat cerebellum (16-18 days gestation) in which more than 90% of cells stained with an anti-neurofilament antibody. Using micro-autoradiography to detect the binding sites, an average of 14% of cells in these cultures with a diameter of 9.2 +/- 0.6 microns were associated with high silver grain densities (greater than 400 grains/100 microns). With some of these cells, silver grains were localised over cell bodies and branching processes characteristic of a neuronal phenotype. A second group of cells with high grain densities were more difficult to classify using morphological criteria and may be non-neuronal. The density of silver grains over the remaining cells was low (less than 20 grains/100 microns 2) and was similar to that measured in nuclear emulsion overlying cultures used to assess non-specific binding. These results indicate that binding sites for all ET peptides are present in both adult rat brain and embryonic cerebellar cultures.(ABSTRACT TRUNCATED AT 250 WORDS)