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Sites linked to the storage and transportation of endothelin (ET) were investigated in human coronary artery. ET-like immunoreactivity was detected in secretory vesicles and storage granules, indicating that the peptide may be transported via both constitutive and regulated secretory pathways. The distribution of ECE-like immunoreactivity was also investigated to determine possible sites involved in the cleavage of big ET-1 to ET-1. Sections of coronary artery labeled with antisera raised against the endothelin-converting enzymes (ECE-1α, ECE-1β, and ECE-2) showed immunoreactive staining over luminal endothelial cells. An en face coronary artery preparation labeled with antisera raised against ECE-1α and ECE-1β revealed only a low level of plasma membrane staining by scanning electron microscopy. The findings indicate cell surface and intracellular expression of ECE in human endothelium.