The mechanisms underlying the switch from uterine quiescence to contractile activity in labour are not understood. There is increasing evidence, however, that myometrial calcium homeostasis is altered dramatically at term and at labour onset. Store-operated calcium (SOC) entry is one such calcium signalling pathway that appears to be up-regulated during gestation (Tribe et al. 2000). Indeed, data from our laboratory suggest there is enhanced SOC entry in myometrium from women in active labour compared with women at term prior to labour (Tribe et al. 2000). The molecular basis of the channels involved in SOC in pregnant human myometrium are unknown, but it is postulated that they may be hetero- or homo-oligomeric assemblies of transient receptor potential channel (TrpC) proteins, which are encoded by mammalian homologues of Drosophila trp genes. The aims of the present study were to (i) determine whether any of the trp genes are expressed in pregnant human myometrium, and (ii) to examine TrpC protein expression and localisation within myometrium.

Human myometrial samples were obtained, with informed written consent and institutional ethics committee approval, at elective Caesarean section prior to labour (38-40 weeks). Tissue samples were snap frozen for RNA (n = 6) or protein (n = 6) isolation. Myometrial samples (n = 12) were also used for cell culture. PCR primers were designed to amplify trp 1, trp 3, trp 4 or trp 6 cDNA fragments. Western blotting was performed using polyclonal antibodies raised against TrpC1 (Xu & Beech, 2001), TrpC3, TrpC4 and TrpC6 (Alamone Labs, Israel). To localise TrpC1, fluorescent immunocytochemisty and confocal microscopy were performed.

RT-PCR amplified fragments of trp 1, trp 3, trp 4 and trp 6 in all samples. PCR products were 100 % homologous to published human sequences. Western blot analysis detected TrpC1, TrpC3, TrpC4 and TrpC6 proteins, which were of expected size. TrpC1 was localised to the membrane and unidentified regions of pregnant human myometrial cells.

These studies have demonstrated that trp 1, trp 3, trp 4 and trp 6 mRNA and proteins are expressed in term pregnant human myometrium. Our data suggest that TrpC1 was present in the plasma membrane and therefore is a putative subunit of SOC in term pregnant human myometrial cells. The role that trp genes play during gestation and active labour remains to be elucidated.This work is supported by The Wellcome Trust (grant no. 061138) and Tommy’s, the baby charity (Registered Charity no. 1060508).

Tribe, R.M., Moriarty, P. & Poston, L. (2000). Biol. Reprod. 63, 748-55.

Xu, S.Z. & Beech, D.J. (2001). Circ. Res. 88, 84-87.