Endothelin in brain: receptors, mitogenesis, and biosynthesis in glial cells

We have explored the cellular loci of endothelin (ET) actions and formation in the brain, using cerebellar mutant mice as well as primary and continuous cell cultures. A glial role is favored by several observations: (i) mutant mice lacking neuronal Purkinje cells display normal ET receptor binding and enhanced stimulation by ET of inositolphospholipid turnover; (ii) in weaver mice lacking neuronal granule cells, ET stimulation of inositolphospholipid turnover is not significantly diminished; (iii) C6 glioma cells and primary cultures of cerebellar astroglia exhibit substantial ET receptor binding and ET-induced stimulation of inositolphospholipid turnover; (iv) ET promotes mitogenesis of C6 glioma cells and primary cerebellar astroglia; and (v) primary cultures of cerebellar astroglia contain ET mRNA. ET also appears to have a neuronal role, since it stimulates inositolphospholipid turnover in primary cultures of cerebellar granule cells, and ET binding declines in granule cell-deficient mice. Thus, ET can be produced by glia and act upon both glia and neurons in a paracrine fashion.