Pacemaking activity in myometrium

Abstract

One of the most intriguing, unanswered questions in uterine physiology is; what mechanism brings about spontaneous activity? As control of uterine activity is so very important for reproductive success, an answer to this question is vital. Despite an increased understanding of the mechanism of contractions and the underlying signalling pathways and changes in [Ca], our ability to prevent pre-term deliveries or dysfunctional labours has improved very little. Over the last few years, specialised cells with features similar to the classical gut pacemakers, the interstitial cells of Cajal (ICC), have been reported in a variety of rhythmic smooth muscles, and the cells referred to as ICC-like cells or modified smooth muscle cells. These cells have been attributed a pacemaker role in some but not all these smooth muscles. In the light of these reports we have examined pregnant rat myometrium for ICC-like cells, using intact preparations and single isolated cells and a variety of techniques (1). Both preparations revealed numerous ICC-like cells, with spider-like projections and enlarged central regions, making them readily distinguishable from myocytes; they were also non-contractile. In current and voltage-clamp experiments we studied their electrical properties. Membrane potential was -58 mV and outward K currents readily recordable. However we were not able to demonstrate any inward currents. We therefore conclude that at least in the rat, ICC-like cells are present but not acting as pacemakers, and suggest that the pacemaker ability resides within myocytes. A role for them remains to be determined. Reference Duquette, RA et al 2005, Biol Repro 72, 276-283 [J Physiol Sci. 2007;57 Suppl:S16]