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The role of the sarcoplasmic reticulum in neonatal uterine smooth muscle: enhanced role compared to adult rat
Author(s) -
Noble Karen,
Wray Susan
Publication year - 2002
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.2002.031732
Subject(s) - myometrium , medicine , endocrinology , cyclopiazonic acid , carbachol , contraction (grammar) , uterus , contractility , endoplasmic reticulum , uterine contraction , muscle contraction , prostaglandin , sensitization , stimulation , chemistry , biology , calcium , microbiology and biotechnology , immunology
Little is known about contractile activity, response to agonists or excitation‐contraction coupling in neonatal smooth muscle. We have therefore investigated 10‐day rat uterus to better understand these processes, and compared it to adult uterus to elucidate how control of contractility develops. Spontaneous contractions are present in the 10‐day neonatal uterus, although they are not as large or as regular as those present in adult tissues. External Ca 2+ entry via L‐type Ca 2+ channels is the sole source of Ca 2+ and is essential for the spontaneous activity. The neonatal uterus was responsive to carbachol or prostaglandin F 2α application; it showed a marked stimulation and a clear dissociation between the force and Ca 2+ changes. Such sensitization was not apparent in adult rat myometrium. The sarcoplasmic reticulum (SR) had more releasable Ca 2+ and contributed more to the response to agonists in neonatal compared to adult tissues. Thus, Ca 2+ entry as opposed to SR Ca 2+ release contributed much less to the uterine response to agonists in the neonatal, compared to adult tissues. Inhibition of the SR by cyclopiazonic acid also caused a more vigorous increase in Ca 2+ and contractile activity, particularly frequency, in the neonatal compared to the adult uterus. Taken together these data suggest that: (1) spontaneous activity is already present by day 10, (2) receptor‐coupling and excitation‐contraction signalling pathways are functional, (3) the SR and Ca 2+ sensitization mechanisms play a more prominent role in the neonate, and (4) there is a shift to a greater reliance on Ca 2+ entry and excitability with development of the myometrium.