Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC357
Properties of interstitial cells in human uterus
H. C. Parkington1, M. A. Tonta1, Q. Li1, J. Iqbal1, P. J. Sheehan2, S. P. Brennecke2, R. J. Lang1, H. A. Coleman1
1. Physiology, Monash University, Clayton, Victoria, Australia. 2. Perinatal Research Centre, Royal Women's Hospital, Melbourne, Victoria, Australia.
Inappropriate contractions remain a significant clinical problem in the labour ward. Suppression of contractions may be required when preterm labour threatens, while on the other hand, failure to progress in labour may necessitate delivery by caesarean section. Despite a good understanding of the mechanisms of contraction, what remains entirely unknown is how contractions are generated. Non-muscle cells resembling interstitial cells (ICs) of Cajal in the gut, have been described in the wall of the uterus (1-4). In the gut, ICs are pivotally involved in the generation and propagation of contractile activity. Our aim was to investigate the possible role of ICs in pacemaking in uterus. Uterine tissue was obtained, following informed written consent, from women undergoing caesarean delivery at term, not in labour (NIL) or in labour (IL). Some tissue was immediately frozen for immunohistochemistry. Strips of tissue were incubated with digestive enzymes for isolation of cells. Single cells were studied using conventional or nystatin perforated patch techniques (5). Intracellular microelectrodes were used to record membrane potential with tension in intact uterine strips. ICs stained with vimentin and they occupied 1.3±0.2% of the intrabundle mass (smooth muscle cells, SMCs, stained with SM actin) NIL and this increased to 2.4±0.3% IL (n=6). Isolated SMCs and ICs from 20 women (NIL) were characterized. SMCs had a robust L-type voltage-gated Ca2+ current, which was all but absent from ICs. Large outward currents occurred in SMCs (904±180 pA at +30mV) but small in ICs (58±10 pA). These currents were reduced by iberiotoxin to 27±5% in SMCs but only to 85±11% in ICs, indicating a large-conductance, Ca2+-activated K+ current (BKCa). Single cell PCR of these characterized cells revealed the presence of KCNMA1, the gene product for BKCa channels, in all 20 SMCs, but was absent in all 20 ICs. In 17 of a further 20 ICs (85%) patch-clamp recording were maintained for greater than 30min. Spontaneous inward currents occurred irregularly with a frequency of 1 per 10±2 min. This current had a duration of 31±4 sec, amplitude of 687±146pA, reversal potential of −9±2mV, and PNa/PK of 0.85 in normal patch and external solutions (n=17). Replacing KCl in the patch pipette with K-gluconate had no effect on the inward current (n=7). Reversal potential was shifted to −36±6 mV (n=6) when external Na+ was reduced from 143 to 40mM. In intact strips, bursts of action potentials accompanied by contractions occurred spontaneously at a frequency of 1 per 12±3 min. The spontaneous depolarizing currents and the lack of BKCa currents would facilitate a pacemaking role for ICs. The ICs had little or no voltage-gated Ca2+, and never contracted. Irregular oscillations in membrane potential have previously been described in ICs under zero current conditions (1) and we now show that these are underpinned by a cation current.
Where applicable, experiments conform with Society ethical requirements