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Expression of Transient Receptor Channel Proteins in Human Fundal Myometrium in Pregnancy

Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado; Department of Biochemistry of Muscles, Palladin Institute of Biochemistry, Kiev, Ukraine; Department of Obstetrics and Gynecology, University of Texas Southwestern Medical School, Dallas, Texas; Department of Obstetrics and Gynecology, University of Texas Medical School at Houston, Houston, Texas; Department of Biomedical Sciences, Campus Deliver #1683, Colorado State University, Fort Collins, CO 80523; cku{at}lamar.colostate.edu

Lidiya Babich, PhD

R. Ann Word, MD

Miao Zhong, PhD

Aida Ulloa

Manju Monga, MD

Barbara M. Sanborn, PhD

Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado; Department of Biochemistry of Muscles, Palladin Institute of Biochemistry, Kiev, Ukraine; Department of Obstetrics and Gynecology, University of Texas Southwestern Medical School, Dallas, Texas; Department of Obstetrics and Gynecology, University of Texas Medical School at Houston, Houston, Texas

Objective: Cation channels comprised of transient receptor potential (TrpC) proteins may play a role in signal-regulated calcium entry and calcium homeostasis in myometrium. The objective of this study was to determine the relative abundance of specific TrpC mRNAs expressed in human myometrium and determine if TrpC mRNA and protein concentrations differ in fundal myometrium before and after the onset of labor.

Methods: A quantitative real-time polymerase chain reaction (Q-RT-PCR) procedure was developed for determining the concentration of TrpC mRNA expression in immortalized and primary human myometrial cells and myometrial fundus tissues from patients before and after the onset of labor. The corresponding TrpC proteins were detected by Western blot analysis and immunohistochemistry.

Results: hTrpC1, 3, 4, 5, 6, and 7 mRNAs were expressed in two lines of immortalized human myometrial cells and in primary human myocytes. In all of these cells, hTrpC1 and hTrpC4 mRNAs were the most abundant, followed by hTrpC6. A similar distribution was observed in fundal myometrium samples from patients before and after the onset of labor. hTrpC4 and mRNA was significantly lower after the onset of labor; there were no significant changes in the concentrations of other TrpC mRNAs. Immunohistochemistry identified hTrpC1, 3, 4, and 6 proteins in myometrial smooth muscle cells. Western blot analysis of myometrial membranes demonstrated no statistically significant changes in hTrpC1, 3, 4, and 6 proteins between samples collected before and after the onset of labor.

Conclusions: We have demonstrated that hTrpC1 and hTrpC4 are the most abundant TrpC mRNAs in human myometrium, with TrpC6 being the next most abundant. There was no increase in TrpC mRNA or protein in fundal myometrium with the onset of labor. Nonetheless, these isoforms may play significant roles in signal regulated calcium entry in human myometrium.

Key Words: TrpC • capacitative calcium entry • myometrium • mRNA • pregnancy

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