Molecular Human Reproduction, Vol 3, 1029-1035, Copyright © 1997 by Oxford University Press
S Sakamoto, S Obayashi, T Aso, J Sato, H Hamasaki and H Azuma
Experiments were performed to characterize endothelin-1-induced
contractions and the role of endothelin (ET) receptor subtypes in rat
myometrium. The binding sites of [(125)I]-ET-1 were saturable with high
affinity. Scatchard plot analysis revealed that ET-1 binding sites in the
myometrium constituted a single population. The dissociation equilibrium
constant (Kd) and the maximum binding sites (Bmax) were determined to be
48.9+/-3.0 pM and 1364.0+/-210.3 fmol/mg protein respectively. Specific
[(125)I]-ET-1 binding was inhibited completely by unlabelled ET-1 and Ro
46-2005 (mixed-type ET receptor antagonist), but not fully (90.7+/-1.4%) by
BQ 123 (a selective ETA receptor antagonist), and not at all by RES 701-1
(a selective ETB receptor antagonist). ET-1 induced myometrial contractions
were composed of two types, an increase in resting tone and rhythmic
contractions. These contractions were inhibited by BQ 123 and Ro 46-2005,
but not by RES 701-1. ET-1-induced contractions were greatly reduced in
Ca2+-free Krebs' solution. Nifedipine abolished the rhythmic contractions
without affecting the increase in resting tone. These results suggest that
ETA receptors are predominantly localized in rat myometrium and that
excitation of ETA receptors evokes two types of contractions by increasing
the cytoplasmic Ca2+ concentration.
JOURNAL ARTICLE
The mechanism of myometrial contractions induced by endothelin-1 in rat
Department of Obstetrics and Gynecology, Faculty of Medicine, Tokyo Medical and Dental University, Japan.
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