Endothelin converting enzyme activity in primary rat astrocytes is modulated by endothelin B receptors

Astrocytes express endothelin-1 (ET-1), ET-3, and their receptors, ET(A) and ET(B). We report here that activated astrocytes in vivo also express endothelin converting enzyme-1 (ECE-1). Higher basal ET-1 concentrations in astrocyte media from ET(B)-deficient (sl/sl) versus wildtype (+/+) rats suggested that altered ECE activity may be related to the absence of ET(B) receptors. Quantification of ECE activity in membranes from sl/sl astrocytes yielded a 50% higher conversion compared to +/+ astrocytes, with indistinguishable ECE-1 mRNA and protein levels. Kinetic analysis of ECE activity revealed similar V(max) values in sl/sl and +/+ astrocytes. Enzyme activity was competitively inhibited by phosphoramidon with K(i) values of 0. 6 and 0.3 microM, respectively. The K(m) value of ECE was 0.5 microM in +/+ and 0.2 microM in sl/sl astrocytes. Two-dimensional focussing of astrocytic ECE-1 uncovered heterogeneity of charge and molecular weight. ECE-1 from sl/sl revealed a glycosylation pattern different from +/+ astrocytes. In conclusion, the ET(B) receptor may, via ECE-1 glycosylation, exert a negative feedback on ECE activity in the astrocytic endothelin system.