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The Role of Interstitial Cells of Cajal in Oviduct Pacemaker Activity
Date
2009Type
DissertationDepartment
Biochemistry and Molecular Biology
Degree Level
Doctorate Degree
Abstract
The experiments described in this dissertation were performed to investigate the
spontaneous electrical activity of the oviduct myosalpinx and to determine its cellular
origin and ionic basis. We have also examined the impact of chlamydia on this activity,
using a murine model of genital chlamydia infection.
In vitro spatio-temporal mapping and video imaging of myosalpinx contractions
and egg and luminal particle movement within the oviduct have revealed that
spontaneous myosalpinx contractions are critical for egg transport along the duct, not
ciliary beating. Intracellular microelectrode recordings and simultaneous isometric force
recordings have shown that slow waves provide the electrical basis for the rhythmic
contractions of the myosalpinx.
Immunohistochemistry against the KIT protein has revealed an extensive network
of ICC-OVI along the length of oviducts. Organotypic culture experiments performed on
P0 oviducts incubated with or without the KIT neutralizing antibody ACK2, have shown
that slow wave activity is absent from oviducts with severely disrupted ICC-OVI
networks, revealing for the first time, that ICC-OVI are the pacemakers of the oviduct.
RT-PCR has revealed transcriptional expression of several Ca2+ and K+
channels
as well as ClCa channels (encoded by Tmem16a) in the oviduct myosalpinx. The ionic
basis of slow wave activity has been thoroughly examined using intracellular
electrophysiology and specific ion channel agonists and antagonists. Adequate
extracellular Ca2+ and intact intracellular Ca2+ stores have been found to be critical for
pacemaker activity. ClCa channel activity has also been determined to be essential for
ii
pacemaker activity, since slow waves are absent from oviducts exposed to the ClCa
channel antagonist niflumic acid and from oviducts taken from animals that are
homozygotes for the null allele of TMEM16A. TREK, KATP and Kv channels are
regulators of slow wave frequency. These three channels along with IK, have all been
found to contribute to the setting of the RMP in the oviduct.
Caffeine has been demonstrated to activate KATP channels in a cAMP-dependent
manner in the oviduct. This causes membrane hyperpolarization, inhibition of slow wave
activity and loss of myosalpinx contractions and may explain why women with high
caffeine intakes take longer to conceive than women who do not consume caffeine.
In oviducts 2 wk post-infection with C. muridarum, slow wave activity has been
found to be absent and ICC-OVI populations were severely disrupted or absent. Damage
to pacemaker activity is suggested to be a result of the host immune response to infection,
more specifically to the upregulation of proinflammatory mediators NOS2 and PTGS2.
Pacemaker activity can be protected from LPS induced inflammatory damage in vitro by
inhibition of NOS2 with 1400W. ICC-OVI networks begin to recover or re-establish and
pacemaker activity returns as the infection is resolved, 4 - 7 weeks post-infection.
In conclusion, this dissertation provides compelling evidence that ICC-OVI
networks are the pacemakers of the oviduct, responsible for generating spontaneous
electrical slow wave activity that underlies the rhythmic contractions of the myosalpinx
which are critical to egg transport. These pacemaker cells are damaged by the host
immune response to chlamydia infection, leading to oviduct stasis and pseudoobstruction and providing an explanation as to why women with a history of chlamydia
infections have an increased risk for ectopic pregnancies and tubal factor infertility.
Permanent link
http://hdl.handle.net/11714/4133Additional Information
Committee Member | Sanders, Kenton M.; Koh, Sang D.; Leblanc, Normand; Kidd, Thomas |
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Rights | In Copyright(All Rights Reserved) |
Rights Holder | Author(s) |