Localization of TASK and TREK,Two-Pore Domain K+ Channels,in Human Cytotrophoblast Cells

Objective: Two-pore domain K⁺ channels (K_2P), an emerging K⁺ channel subfamily, contribute to setting membrane potential in both electrically excitable and nonexcitable cells and, as such, influence cellularfunction. The multinucleate syncytiotrophoblast of human placenta, formedfrom thefusion of mononucleate cytotrophoblast cells, is a transporting epithelium whosefunction likely depends on the activity of K⁺ channels. We have therefore investigated the gene expression of two members of this family, TASK and TREK, in cultured human cytotrophoblast cells, and have also investigated protein expression in cytotrophoblast cells and placenta.

Methods: We used reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunocytochemistry to investigate the gene and protein expression of TASK and TREK isoforms in both isolated cytotrophoblast cells and term placental tissue.

Results: In cytotrophoblast cells, mRNAs encoding TASK1, 2, 4, 5, and TREK1 were detected, whereas weak or no signals were observedfor TASK3 and TREK2. Western blottingfor TASK1 in cytotrophoblast cells gave two bands of approximately 78 and 150 kd; TREK1 gave bands of approximately 90 and 130 kd. TASK1 immunofluorescence in placenta colocalized with cytokeratin-7, a trophoblast specific marker. TREK1 predominantly stained cells around the villous perimeter and this staining was colocalized with propidium iodide nuclear staining.

Conclusion: Human cytotrophoblast cellsfrom term placenta are a site of expression for various K_2p genes, two of which, namely, TASK1 and TREK1, are transcribed into protein.