Fine spatiotemporal calcium signals and kinematic properties revealed by motion-corrected calcium images of contracting myometrium

• Main Author: Loftus, Fiona C.
• Published: University of Warwick 2015
• Subjects: 618.4; QP Physiology
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685200

Successful childbirth depends on precisely coordinated uterine contractions during labour. Calcium indicator fluorescence imaging is one of the main techniques for investigating the mechanisms governing this physiological process and its pathologies. The effective spatiotemporal resolution of calcium signals is, however, limited by the motion of contracting tissue: structures of interest that are of the order of microns can move over a hundred times their width during a contraction. The simultaneous changes in local intensity and tissue configuration make motion tracking a nontrivial image-analysis problem and confound many of the standard techniques. In this thesis I present a method that tracks local motion throughout the tissue allowing for an almost complete removal of motion artifacts. This provides a stabilised calcium signal down to a pixel resolution which, for the data examined, is of the order of a few microns. As a byproduct of the image stabilisation, a complete kinematic description of the contraction-relaxation cycles is also obtained containing novel information about the mechanical response of the tissue, such as the identification of a characteristic length scale, of the order of 40-50 microns, below which tissue motion is homogeneous. This kinematic information will help to fill the gaps in experimentally recorded mechanical properties of contracting myometrium. Applying the algorithm to over twenty datasets, I show that for the first time unrestricted single-cell calcium measurements can be taken from myometrial tissue slices over multiple contraction-relaxation cycles. I investigate single-cell calcium signals in between contractions and compare single-cell calcium dynamics in control and oxytocin-treated myometrium. Additionally, I use the kinematics of tissue motion to compare calcium signals at the subcellular level and local contractile motion. Freely modifiable code written in the MATLAB environment was published under the GNU General Public license in the hope that it will be useful to researchers analysing these or similar datasets.