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, ETA and ETB. We report here that activated astrocytes in vivo also express endothel in converting enzyme-1 (ECE-1). Higher basal ET-1 concentrations in astrocy te media from ETB-deficient (sl/sl) versus wildtype (+/+) rats suggested th at altered ECE activity may be related to the absence of ETB receptors. Qua ntification 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 simila r V-max values in sl/sl and +/+ astrocytes. Enzyme activity was competitive ly inhibited by phosphoramidon with K-i values of 0.6 and 0.3 mu M, respect ively. The K-m value of ECE was 0.5 mu M in +/+ and 0.2 mu M in sl/sl astro cytes. Two-dimensional focussing of astrocytic ECE-1 uncovered heterogeneit y of charge and molecular weight. ECE-1 from sl/sl revealed a glycosylation pattern different from +/+ astrocytes. In conclusion, the ETB receptor may , via ECE-1 glycosylation, exert a negative feedback on ECE activity in the astrocytic endothelin system. (C) 1999 Academic Press.