Phasic Contractions of the Mouse Vagina and Cervix at Different Phases of the Estrus Cycle and during Late Pregnancy

Abstract

Background/AimsThe pacemaker mechanisms activating phasic contractions of vaginal and cervical smooth muscle remain poorly understood. Here, we investigate properties of pacemaking in vaginal and cervical tissues by determining whether: 1) functional pacemaking is dependent on the phase of the estrus cycle or pregnancy; 2) pacemaking involves Ca2+ release from sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) -dependent intracellular Ca2+ stores; and 3) c-Kit and/or vimentin immunoreactive ICs have a role in pacemaking.Methodology/Principal FindingsVaginal and cervical contractions were measured in vitro, as was the distribution of c-Kit and vimentin positive interstitial cells (ICs). Cervical smooth muscle was spontaneously active in estrus and metestrus but quiescent during proestrus and diestrus. Vaginal smooth muscle was normally quiescent but exhibited phasic contractions in the presence of oxytocin or the K+ channel blocker tetraethylammonium (TEA) chloride. Spontaneous contractions in the cervix and TEA-induced phasic contractions in the vagina persisted in the presence of cyclopiazonic acid (CPA), a blocker of the SERCA that refills intracellular SR Ca2+ stores, but were inhibited in low Ca2+ solution or in the presence of nifedipine, an inhibitor of L-type Ca2+channels. ICs were found in small numbers in the mouse cervix but not in the vagina.Conclusions/SignificanceCervical smooth muscle strips taken from mice in estrus, metestrus or late pregnancy were generally spontaneously active. Vaginal smooth muscle strips were normally quiescent but could be induced to exhibit phasic contractions independent on phase of the estrus cycle or late pregnancy. Spontaneous cervical or TEA-induced vaginal phasic contractions were not mediated by ICs or intracellular Ca2+ stores. Given that vaginal smooth muscle is normally quiescent then it is likely that increases in hormones such as oxytocin, as might occur through sexual stimulation, enhance the effectiveness of such pacemaking until phasic contractile activity emerges.

Uterine Contractility in the Nonpregnant Mouse: Changes During the Estrous Cycle and Effects of Chloride Channel Blockade1

“…The Kit-immunopositive structure observed was inconsistent with ICC-like Kitimmunoreactivity in the small intestine in that it did not form part of an anastomosing network. Similar disparate spindle-shaped Kit-immunopositive structures have been reported in the cervix but not in the vagina of the mouse [18]. Our observations lead us to preclude Kit-expressing ICLCs as the cell type responsible for generating spontaneous uterine contractility in the nonpregnant mouse uterus.…”

Cloprostenol and eCG influence oestrus synchronisation and uterine development in mice

“…the prooestrus, oestrus, metoestrus and dioestrus stages. The results were consistent with previous reports (Fu et al 2005;Zhu et al 2012;Gravina et al 2014). …”

Chlamydia muridarum infection differentially changes smooth muscle contractility and responses to prostaglandins in uterus and cervix

“…This period was sufficient for the infection to induce adaptive immune responses around the FRT that resembles chronic Chlamydia infection and the inception of hydrosalpinx in infected mice (unpublished data). Then, mice were sacrificed by sodium pentobarbitone overdose, and vaginal lavages were collected for estrous cycle confirmation as previously described [14,39]. Left uterine horn was dissected out, trimmed of visceral fat, snap-frozen in liquid nitrogen (N 2 ) and stored at -80C until needed.…”

“…Whether this extends to the lower region of the female reproductive tract (FRT) remains unknown. The uterus and cervix, just like the oviducts, contract spontaneously in the non-pregnant state in human and mouse [11][12][13][14].…”

“…Apart from spontaneous contraction, smooth muscles along the FRT are also responsive to endocrine, paracrine and neuronally released signalling molecules. The hormone oxytocin increases uterine [17][18][19][20], cervical and vaginal motility [14]. Prostaglandins signalling is recognized in modulating uterine motility [21].…”