Synchronised oscillations that take place in biological systems have elicited a lot of interest and study. In this context, the behaviour of the uterus towards late pregnancy and close to labour, when it goes into sychronised oscillations seeks to be understood.
A paper published in February 2012 in the journal, Physical Review Letters, by a group of scientists from India and France, which includes Rajeev Singh and Sitabhra Sinha of the Institute of Mathematical Sciences, Chennai, gives an theoretical explanation for the observed rhythmic contractions of the uterus during and just before labour. The paper provides the understanding that these synchronised oscillations in the uterus do not arise from any central agency (like the pacemaker cells do for the heart). Instead they emerge due to some electrophysiological changes that take place in the uterus.
What these electrophysiological changes are and how they affect the uterus can be understood by considering the structure of the uterine tissue. It consists of electrically excitable smooth muscle cells as well as electrically passive cells. In the tissue, cells are coupled by gap junctions that serve as electrical conductors. These gap junctions have been studied and are found to increase, both in number and value of electrical conductance, markedly during late pregnancy. The correlation between this electrophysiological change and the corresponding tendency of the uterus to go into rhythmic contractions strongly suggests a prominent role of the coupling between the cells.
Hence the group has modelled the uterus as a two-dimensional grid occupied by electrically excitable cells, each of which is coupled to one or more passive cells and to its neighbouring excitable cells with a particular strength of intercellular interaction. Solving the emerging equations they find that when this strength is increased step by step, the system goes through wavelike excitations that “lead to coherent periodic activity, exhibiting cluster, local and global synchronisation under different conditions.” Namely, as the strength of intercellular interaction increases, localised regions oscillating at different frequencies tune in to a single frequency but with a few local regions of inactivity. Further increasing the strength cause the whole system to oscillate in a single wave.
“Our model was successful in that it is not only a simple and appealing explanation of how self-organized oscillations arise from interactions between non-oscillating cells but also in connecting two well-known empirical observations: as pregnancy progresses, coupling between cells become stronger, and the muscle activity becomes more and more coherent and rhythmic,” says Sitabhra Sinha, one of the authors of the paper.
Understanding the mechanism behind the functioning of the uterus is important because in 10 per cent of all pregnancies rhythmic contractions are initiated early, causing preterm births. A better understanding of the way the uterus functions could go a long way in helping to mitigate this problem.