INCREASED CONTRACTILITY OF RAT UTERINE SMOOTH-MUSCLE AT THE END OF PREGNANCY

Citation
Bk. Kim et al., INCREASED CONTRACTILITY OF RAT UTERINE SMOOTH-MUSCLE AT THE END OF PREGNANCY, Comparative biochemistry and physiology. Part A, Molecular & integrative physiology, 121(2), 1998, pp. 165-173
Citations number
32
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Zoology,Physiology,Biology
ISSN journal
1095-6433
Volume
121
Issue
2
Year of publication
1998
Pages
165 - 173
Database
ISI
SICI code
1095-6433(1998)121:2<165:ICORUS>2.0.ZU;2-I
Abstract
Upon stimulation with high K+, oxytocin, prostaglandin E-2, prostaglan din F(2)alpha or carbachol, myometrium isolated from pregnant rats (21 days after pregnancy) developed 2-3 times greater isometric force tha n that from non-pregnant rats (estrus). High K+ increased the level of myosin light chain (MLC) phosphorylation to a similar extent in these tissues, and therefore pregnant myometrium developed greater contract ion than non-pregnant myometrium at a given MLC phosphorylation. In th e permeabilized muscle with oc-toxin, Ca2+ (0.1-10 mu M) induced great er contraction in pregnant myometrium than in non-pregnant myometrium. Ca2+ sensitivity was not altered after pregnancy. MLC kinase and phos phatase activities did not differ significantly between pregnant and n on-pregnant myometria. Stimulation with 10 mu M Ca2+ and 1 mu M calycu lin-A elicited similar magnitudes of contractions in the permeabilized muscles isolated from non-pregnant and pregnant rats. SDS-PAGE showed that the percentage of the content of MLC was not altered between the se preparations, although actin content increased after pregnancy. The se results suggest that the stress generating capacity of myometrium i s increased after pregnancy without changing the MLC phosphorylation s tep. The equal capacity of force generation after the maximum phosphor ylation by Ca2+ and phosphatase inhibitor suggests that a MLC phosphor ylation-independent mechanism is responsible for the development of gr eater force in the pregnant myometrium. (C) 1998 Elsevier Science Inc. All rights reserved.