PROPERTIES OF RAT UTERUS ENDOTHELIN RECEPTOR-SITES

Endothelin-binding sites in rat uterus have been characterized in terms of ligand specificity and molecular weight. Contractile responses of uterus horns to endothelin analogues were first examined; endothelin-l and endothelin-2 caused rhythmic contractions at l nM and developing monophasic contractions at l0 nM; however, in the case of endothelin-3, much higher concentrations were required to induce the rhythmic (50 nM) and developing (500 nM) contractions. These responses are unique since in the vascular system all the three members of the endothelin have been demonstrated to be active at subnanomolar concentrations. Consistent with these results of physiological response analysis, binding assays using radioligands revealed that rat uterus bound 125I-endothelin-1 with a high affinity but it showed only a weak affinity for 125I-endothelin-3. The rank order of binding potency determined by competitive binding assay was: endothelin-1≥endothelin-2>>endothelin-3. Affinity labeling of the binding sites on the uterus membranes using 125I-endothelin and the cross-linking reagent 1,5-difluoro-2,4-dinitrobenzene showed one major band with an Mr of 48,500. These results indicate that the rat uterus endothelin receptor site is a 46 K membrane protein and specific for endothelin-l and endothelin-2. © 1990, Biomedical Research Press. All rights reserved.