Orai1 protein expression and the role of calcium release-activated calcium channels in the contraction of human term-pregnant and non-pregnant myometrium.

AIM: This experimental in vitro study examined differences in the expression and activity of calcium release-activated calcium (CRAC) channels of human term-pregnant and non-pregnant myometrium. MATERIAL AND METHODS: The tissue samples were obtained from term-pregnant myometrium in labor of women undergoing cesarean section and from non-pregnant myometrium of women undergoing total hysterectomy due to uterine myoma. The expression of Orai1 protein, a pore-forming subunit of CRAC channels, in human myometrium was examined using immunohistochemistry. CRAC channel involvement in the amplitude and frequency of myometrial contractions was evaluated in vitro using a tissue bath method with a CRAC ion channel blocker 3-fluropyridine-4-carboxylic acid (FPCA). RESULTS: Decreased Orai1 expression was observed in human term-pregnant laboring myometrium compared with non-pregnant myometrium. However, the initial oxytocin-induced contraction of myometrium was significantly suppressed at different doses of FPCA in both non-pregnant human isolated myometrium and non-pregnant myometrium. The frequency of contractions was the most significantly reduced at the lowest dose of FPCA in non-pregnant myometrium and remained suppressed at all doses of FPCA in term-pregnant myometrium. Salbutamol was shown as more effective in suppression of amplitude in term-pregnant isolated myometrium. CONCLUSION: Our results provide the first information about the changes in the Orai1 protein expression and activity of human myometrial CRAC channels in term-pregnant laboring myometrium.