There is increasing functional evidence for store-operated calcium entry (SOCE) in human myometrium. SOCE appears to be enhanced in human myometrium at labour onset (Tribe et al. 2000) and IL-1β, a cytokine implicated in labour, induces calcium oscillations and SOCE in human myometrial smooth muscle cells (Tribe et al. 2003). TrpC1, 3, 4 and 6 proteins, which are associated with SOCE in other cells, are expressed in pregnant human myometrial tissue (Dalrymple et al. 2002). In this study we determined whether TrpC1, 3, 4, 6 and 7 mRNA and proteins change with pregnancy and labour.

Human myometrium was obtained at Caesarean section (with written consent from women without underlying disease) at term not in labour (TNL, n = 13, 38-41 weeks), term active labour (TAL, n = 13, 39-42 weeks). Non-pregnant myometrium was also collected with written consent at hysterectomy (NP, n = 6). mRNA and total proteins were isolated from myometrial tissue and TrpC expression determined using RT-PCR and Western blotting (Dalrymple et al. 2002). RT-PCR and Western blots were analysed using Bio-Rad scanning software. Values are expressed in arbitrary absorbance units as means ± S.E.M. Significant difference (P < 0.05) was determined using ANOVA with Tukey-Kramer’s multiple comparison test.

TrpC1 protein expression was not detected in NP myometrium but significantly increased in TAL and TNL samples (NP, 0.000 ± 0.000; TAL, 0.076 ± 0.020; TNL, 0.074 ± 0.014; P < 0.05). There was no significant difference in TrpC1 protein expression between TNL and TAL samples. TrpC3 protein expression was minimal in the NP and TNL myometrium, but expression was significantly increased in TAL (NP, 0.003 ± 0.003; TAL, 0.062 ± 0.009; TNL, 0.022 ± 0.007; P < 0.01). TrpC4 protein expression was not detected in NP myometrium, was minimally expressed in TNL and significantly increased in TAL samples (NP, 0.000 ± 0.000; TAL, 0.118 ± 0.039; TNL, 0.018 ± 0.007; P < 0.05). TrpC6 protein expression was not detected in the NP myometrium, minimally expressed in TNL but was significantly increased in TAL myometrial samples (NP, 0.000 ± 0.000 vs. TAL, 0.072 ± 0.012, P < 0.01; TAL vs. TNL 0.036 ± 0.007, P < 0.05). RT-PCR data mirrored protein data for all genes except TrpC4, where mRNA expression was similar between NP, TNL and TAL samples. Pregnancy is associated with an increase in myometrial expression of TrpC isoforms and there is a further increase in TrpC3, 4, and 6 with labour. The functional impact of these data warrants further study.

This work was supported by the Wellcome Trust, Grant No: 061138 and Tommy’s, the baby charity.