AJP - Cell Physiology, Vol 246, Issue 3 216-C223, Copyright © 1984 by American Physiological Society
Activity of circular muscle of rat uterus at different times in pregnancy
B. Bengtsson, E. M. Chow and J. M. Marshall
During pregnancy, circular muscle activity changes from weak irregular
contractions at midterm to strong regular contractions at term. The present
study was designed to determine if this change is related to contractile
ability or to membrane electrical events. Myometrial segments were taken
from rats on days 16-17, 18-19, 20, and 21 (term) of gestation. Contractile
ability was estimated as the maximum force elicited by 121 mM KCl or 0.6 mM
acetylcholine. The K- and acetylcholine-induced contractions were
significantly greater than spontaneous and no different at midterm and
term. Electrical activity was measured with intracellular electrodes.
Between days 16 and 21, action potentials evolved from single, plateau-type
to repetitive spike trains. Plateau potentials were associated with small
contractions and repetitive spikes with larger contractions. On day 21,
there was a transient increase in membrane potential and cessation of
spontaneous activity. Before delivery, the membrane potential declined and
spontaneous spike trains appeared and triggered large contractions.
Conclusion: the change in circular muscle activity during pregnancy is
related to electrical events and not to contractile ability.
