Endothelin degradation by vascular smooth muscle cells

Hakan Bermek, Kou Cheng Peng, Krassimira Angelova, Adviye Ergul, David Puett

Research output: Contribution to journalArticle

9 Scopus citations

Abstract

The mechanism(s) of degradation of the potent vasoconstrictor endothelin-1 (ET-1) by rat vascular smooth muscle A-10 cells, which possess the ET, receptor subtype, was investigated by incubating [125I]ET-1 (0.1 nM) with cells for 0-4 h at 37°C in the presence and absence of lysosomal enzyme inhibitors, NH4Cl and chloroquine, and a neutral endopeptidase inhibitor, phosphoramidon. The assay buffer and cell extracts were analyzed by reverse-phase HPLC, and the radioactivity in the fractions was measured. In the absence of inhibitors, most of the radioactivity in the medium was in the form of [125I]Tyr after a 4 h incubation. When [125I]ET-I was incubated with A-10 cells at 4°C, six radiolabeled peaks, including some [125I]Tyr and about 30% of the original [125I]ET-1, were present in the medium. In the presence of 5 μM chloroquine there was no [[125I]Tyr peak in the medium, indicating that internalization and putative lysosomal degradation of ET-1 were blocked. NH4Cl (50 and 100 mM) also reduced the amount of [125I]Tyr formed. The presence of ET-1 fragments indicated that, in addition to lysosomal degradation, some of the ligand is metabolized by enzymes located on the cell membrane; we demonstrated, however, that secreted proteases from A-10 cells are not involved in the degradation of ET-1. The neutral endopeptidase inhibitor, phosphoramidon, did not completely inhibit the metabolism of [125I]ET-1 to [125I]Tyr. These results establish that various cell-associated enzymes are capable of degrading ET-1 in A-10 cells. Moreover, analysis of the cell lysates indicated the presence of a relatively stable pool of ET-1-occupied receptors or compartmentalized ET-1, protected from cell proteases, which may contribute to the potent contractility of ET-1.

Original languageEnglish (US)
Pages (from-to)155-162
Number of pages8
JournalRegulatory Peptides
Volume66
Issue number3
DOIs
StatePublished - Oct 22 1996

Keywords

  • A-10 cell
  • Degradation
  • Endothelin-1
  • Internalization
  • Lysosome

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Endocrinology
  • Clinical Biochemistry
  • Cellular and Molecular Neuroscience

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