AJP - Endocrinology and Metabolism, Vol 267, Issue 2 E242-E249, Copyright © 1994 by American Physiological Society
Endothelin-1 conversion and receptor characterization in human placental arteries
B. M. Wilkes, C. M. Macica and P. F. Mento
Department of Medicine, North Shore University Hospital, Manhasset, New York.
Endothelin-1-(1-21), a potent pressor peptide, is transcribed as big
endothelin-(1-38) and converted to active peptide by endothelin-converting
enzyme. The current investigation tested the hypothesis that human
fetoplacental blood vessels convert big endothelin-1 to active peptide and
that fetoplacental blood vessels respond to endothelin-1 by binding of the
peptide to specific receptor sites. In the isolated perfused placental
cotyledon the addition of big endothelin-1 to the perfusate caused a
time-dependent increase in perfusion pressure that corresponded to the
appearance of endothelin-1 in the perfusate. The properties of human
placental endothelin-1 receptors were defined in binding studies performed
on a plasma membrane fraction of small arteries (<1.0 mm) dissected from
the placenta. Binding was saturable, reached steady state by 3 h at 25
degrees C, and was linear with protein concentration. Scatchard analysis of
binding data indicated a single class of high-affinity binding sites with a
dissociation constant of 27.6 +/- 2.3 pM and a density of 856 +/- 119
fmol/mg protein (n = 5). The potency order for competitive inhibition of
the binding of 125I-labeled endothelin-1 [endothelin-1 = endothelin-2 >
endothelin-3 = sarafotoxin S6b >> big endothelin-1 (human) = big
endothelin-1 (porcine)] is most consistent with a type A endothelin
receptor subtype. Phenylephrine, bradykinin, norepinephrine, atrial
natriuretic factor, diltiazem, U-46619, and angiotensin II did not displace
125I-endothelin-1 binding. Endothelin receptors were shown to have an
approximate molecular weight of 36,600 by polyacrylamide gel
electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)
