AIM: This study was designed to characterize the en-dothelin pathway in an immortalized human adenocarcino-ma-derived alveolar epithelial cell line (A549) and human umbilical vein endothelial cell line (HUVEC). METHODS: The release of BT-1 and big-ET-1 was measured in the incubation medium of both cell lines. The expression of mRNAs coding for the endothelin iso-forms (hppET-1, -2, -3), the endothelin converting enzymes (hECE-la, b, c, and d) and the hETA and hETB receptors was investigated using RT-PCR. The expression of ECE-1 mRNA in various human tissues and in A549 cells was investigated by Northern blot analysis and the subcellular localization of ECE-1 in A549 cells was investigated by immunoblotting using a polyclonal antibody. RESULTS: Under control conditions, HUVEC release both ET-1 and big-ET-1 (ratio 5 to 1) while in A549 cells the big-ET-1 levels were below the threshold of detection. The release of these two peptides was minimally affected by various inhibitors of peptidases. However, in b AIM: This study was designed to characterize the en-dothelin pathway in an immortalized human adenocarcinoma-derived alveolar epithelial cell line (A549) and human umbilical vein endothelial cell line (HUVEC). METHODS: The release of BT-1 and big -ET-1 was measured in the incubation medium of both cell lines. The expression of mRNAs coding for the endothelin iso-forms (hppET-1, -2, -3), the endothelin converting enzymes (hECE-la, b, c , and d) and the hETA and hETB receptors were investigated using RT-PCR. The expression of ECE-1 mRNA in various human tissues and in A549 cells was investigated by Northern blot analysis and the subcellular localization of ECE-1 in A549 cells was investigated by immunoblotting using a polyclonal antibody. RESULTS: Under control conditions, HUVEC release both ET-1 and big-ET-1 (ratio 5 to 1) while in A549 cells the big-ET-1 levels were below the threshold of detection. The release of these two peptides was minimally affected by various inhibitors of peptida ses. However, in b