Conversion of big endothelin-1 to endothelin-1 by two-types of metalloproteinases of cultured porcine vascular smooth muscle cells.

Incubation of big endothelin-1 (big ET-1, 1-39) with the membrane fraction obtained from cultured vascular smooth muscle cells (VSMCs) resulted in an increase in immunoreactive-ET (IR-ET), which was inhibited by EDTA but not by phosphoramidon, a metalloproteinase inhibitor. When the incubation was performed in the presence of N-ethylmaleimide (NEM), the generation of IR-ET was markedly augmented and this augmentation was abolished by phosphoramidon. The pH profile for IR-ET generation in the presence of NEM was apparently distinct from that observed in the absence of NEM. Reverse-phase HPLC of the incubation mixture with or without NEM revealed one major IR-ET component corresponding to the elution position of synthetic ET-1 (1-21). When the cultured VSMCs were incubated with big ET-1, a conversion to the mature ET-1 was observed. This ET-1 generation from exogenously applied big ET-1 was markedly inhibited by the addition of phosphoramidon, although the inhibitor did not influence the basal secretion of ET-1-like materials. These results suggest the presence of two types of metalloproteinases, which can generate ET-1, in VSMCs. The possibility that ET-1 functions in an autocrine manner to control the cardiovascular system warrants further attention.