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Electrical properties of the costo‐uterine muscle of the guinea‐pig.
Author(s) -
Parkington H C
Publication year - 1983
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1983.sp014515
Subject(s) - myometrium , guinea pig , biophysics , endocrinology , chemistry , resting potential , membrane potential , medicine , smooth muscle , calcium , membrane , myocyte , uterus , biology , biochemistry
The spontaneous electrical and mechanical activity of the costo‐uterine muscle of the guinea‐pig are described. The spontaneous electrical activity, recorded intracellularly, is similar to that observed previously in longitudinal myometrium of rat (Marshall, 1959) and ionic substitution suggests that, though calcium may be the predominant ion carrying the current during the upstroke of the action potential, some influence of sodium cannot be ruled out. During dioestrus, when circulating progesterone levels are high, there is an increase in the resting membrane potential and a decrease in the frequency of electrical and mechanical activity. There is a two‐fold decrease in the space constant (lambda) during dioestrus. At this time the membrane time constant (tau m) is also decreased. The diameter and length of the smooth muscle cells are smaller during dioestrus. However, the differences in cell diameter do not explain all of the differences observed in lambda at this time and it is suggested that there may be an increase in the resistance to current flow between cells. It is concluded that high circulating progesterone may bring about quiescence of target smooth muscle in two ways: by stabilizing the cell membrane and by restricting the spread of activity.