To investigate the relationship between the oxytocin (OT) receptor (OTR) quantity and the contractile features systematically, we measured the mRNA expression levels of OTR and L-type Ca2+ channel α 1C-subunit (α1C) and examined the regulatory mechanisms of OT-induced phasic or tonic contractions of the longitudinal smooth muscles in mouse uteri. The mRNA expression of OTR in 19.0 G (19.0 days of gestation) was greater than those in nonpregnant phases, and that of α1C in estrus and 19.0 G was higher than in diestrus. OT-induced contractions sparsely occurred in diestrus. The OT-induced all-or-none-type phasic contractions at low concentrations were abolished by verapamil in both estrus and 19.0 G. OT-induced tonic contractions had similar pD2 values in both estrus and 19.0 G. However, the magnitude in 19.0 G was much greater than that in estrus. The large tonic contractions also occurred in PGF2α receptor (FP) knockout mice in 19.0 G despite a small amount of OTR. Verapamil and Y-27632 partially inhibited the tonic contractions in 19.0 G. Cyclopiazonic acid-induced tonic contractions were reciprocally decreased with the increase in the OT-induced ones in 19.0 G. These results indicate that the phasic contractions are dependent on α1C. The tonic contractions in 19.0 G are dependent on both Ca2+ influxes via L-type Ca2+ channels and store-operated Ca2+ channels, and the force is augmented by the Rho signal pathway, which increases the Ca2+ sensitivity. Thus the uterine contractions are mainly controlled by the modification of contractile signal machinery rather than simply by the OTR quantity.
|Journal||American Journal of Physiology - Endocrinology and Metabolism|
|Publication status||Published - Apr 2007|
All Science Journal Classification (ASJC) codes
- Endocrinology, Diabetes and Metabolism
- Physiology (medical)