Phosphoramidon-sensitive endothelin converting enzyme in cultured vascular smooth muscle cells converts big endothelin-3 to endothelin-3.

Incubation of big endothelin-3 (big ET-3, 1-41) with the membrane fraction obtained from cultured vascular smooth muscle cells (VSMCs) resulted in time-dependent increases in immunoreactive-ET (IR-ET), which were suppressed by phosphoramidon. Analysis of the incubation mixture by reverse-phase high performance liquid chromatography (RP-HPLC) confirmed that the IR-ET was due to the mature ET-3 (1-21). ET-1 (1-21) generated during incubation of big ET-1 (1-39) with the membrane fraction was markedly suppressed by the addition of big ET-3 into the incubation mixture. When the cultured VSMCs were incubated with big ET-3, a conversion to the mature ET-3 was observed. This ET-3 generation from exogenously applied big ET-3 was also suppressed by phosphoramidon. We conclude that the phosphoramidon-sensitive ET converting enzyme in VSMCs converts big ET-1 and big ET-3 to their mature form.