COUPLING OF ET(B) ENDOTHELIN RECEPTOR TO MITOGEN-ACTIVATED PROTEIN-KINASE STIMULATION AND DNA-SYNTHESIS IN PRIMARY CULTURES OF RAT ASTROCYTES

Astrocytes have been shown to express endothelin (ET) receptors functi onally coupled, via different heterotrimeric G proteins, to several in tracellular pathways, To assess the relative contribution of each subt ype in the astrocytic responses to ET-1, effects of BQ123, an antagoni st selective for the ET receptor subtype A (ET(A)-R), and IRL1620, an agonist selective for the ET receptor subtype B (ET(B)-R), were invest igated in primary cultures of rat astrocytes, Binding experiments indi cated that the ET(B)-R is the predominant subtype in these cells. Inhi bition of forskolin-stimulated cyclic AMP production was observed unde r ET(B)-R stimulation, Bordetella pertussis toxin (PTX) pretreatment c ompletely abolished this effect, indicating that this pathway is coupl ed to the ET(B)-R via G(i) protein. Increases of tyrosine phosphorylat ion of cellular proteins, stimulation of mitogen-activated protein kin ase (MAPK), and DNA synthesis were also found to be mediated by the ET (B)-R, but through PTX-insensitive G protein, IRL1620-induced MAPK act ivation involved the adapter proteins She and Grb2 and the serine/thre onine kinase Raf-1. This study reveals that the various effects of ET- 1 in astrocytes are mediated by the ET(B)-R, which couples to multiple signaling pathways including the MAPK cascade.