Receptor binding activity and cytosolic free calcium response by synthetic endothelin analogs in cultured rat vascular smooth muscle cells

Using a variety of synthetic analogs of porcine endothelin (pET), we have studied the effects of these analogs on receptor binding activity and cytosolic free Ca2+ concentrations (Ca2+]i) in cultured rat vascular smooth muscle cells (VSMC). Removal of C-terminal Trp21 residue, truncated derivatives pET(1-15) and (16-21), substitution of disulfide bond, Cys(3-11) or Cys(1-15), by Cys (Acm), all resulted in a complete loss of receptor binding activity and Ca2+]i response, while N-terminal elongation of Lys-Arg residues, but not oxidation of Met7 residue, decreased receptor binding activity and Ca2+]i response. Cys1-15,Cys3-11]pET was far more potent than Cys1-11,Cys3-15]pET in receptor binding and Ca2+]i response. These data indicate that the C-terminal Trp21 as well as the proper double cyclic structure formed by the intramolecular disulfide bonds of the pET molecule are essential for receptor binding and subsequent Ca2+]i increase in rat VSMC.