ALUNG April 22/4

Elena Tchekneva, Mayme L. Lawrence, and Barbara Meyrick. Cell-specific differences in ET-1 system in adjacent layers of main pulmonary artery. A new source of ET-1. Am J Physiol Lung Cell Mol Physiol 278: L813–L821, 2000.— Endothelin-1 (ET-1) is a potent vasoconstrictor that causes sustained constriction of the pulmonary artery and modulates normal vascular tone. Endothelial cells were thought to be the major source of ET-1, but recent studies show that vascular smooth muscle cells (SMCs) are also capable of its synthesis. We examined the ET-1 and endothelin-converting enzyme-1 (ECE-1) system in cells cultured from two adjacent layers, subendothelial (L1) and inner medial (L2), of normal sheep main pulmonary artery and the response of this system to exogenous ET-1 and transforming growth factor-b1 (TGFb1). End points include assessment of preproET-1 (ppET-1) and ECE-1 gene coexpression, measurement of intracellular and released ET-1, and ECE-1 activity. RT-PCR analysis revealed that ppET-1 and ECE-1 transcripts were greater in L1 than in L2 cells. The L1 cells also synthesized (L1, 3.2 6 0.1; L2, 1.2 6 0.1 fmol/106 cells) and released (L1, 9.2 6 0.5; L2, 2.3 60.1 fmol/ml) greater amounts of ET-1 than L2 cells. The L2 cells internalized exogenous ET-1 in a dose-dependent manner (EC50 8 nmol/l) and were more responsive to exogenous ET-1 than L1 cells, showing upregulation of both the ppET-1 and ECE genes. TGF-b1 downregulated ET-1stimulated ppET-1 and ECE-1 transcripts but only in L2 cells. In addition, L1 cells showed greater ECE-1 activity than L2 cells, and in both, the activity was sensitive to the metalloprotease inhibitor phosphoramidon. We conclude that the ET-1 system in L1 and L2 cells is distinct. The data suggest that the two cell types have diverse functions in the arterial wall; the L1 cells, like endothelial cells, provide a local source of ET-1; and since the L2 cells are more responsive to exogenous ET-1, they are likely to affect normal pulmonary vascular tone.