Higher Expression of TRPM7 Channels in Murine Mature B Lymphocytes than Immature Cells

  • Kim, Jin-Kyoung (Department of Anesthesiology and Pain Medicine, Samsung Medical Center) ;
  • Ko, Jae-Hong (Department of Physiology and Biophysics, Seoul National University College of Medicine) ;
  • Nam, Joo-Hyun (Department of Physiology, Sungkyunkwan University School of Medicine) ;
  • Woo, Ji-Eun (Department of Physiology, Sungkyunkwan University School of Medicine) ;
  • Min, Kyeong-Min (Department of Physiology, Sungkyunkwan University School of Medicine) ;
  • Earm, Yung-E (Department of Physiology and Biophysics, Seoul National University College of Medicine) ;
  • Kim, Sung-Joon (Department of Physiology and Biophysics, Seoul National University College of Medicine)
  • Published : 2005.04.21

Abstract

TRPM7, a cation channel protein permeable to various metal ions such as $Mg^{2+}$, is ubiquitously expressed in variety of cells including lymphocytes. The activity of TRPM7 is tightly regulated by intracellular $Mg^{2+}$, thus named $Mg^{2+}$-inhibited cation (MIC) current, and its expression is known to be critical for the viability and proliferation of B lymphocytes. In this study, the level of MIC current was compared between immature (WEHI-231) and mature (Bal-17) B lymphocytes. In both cell types, an intracellular dialysis with $Mg^{2+}$-free solution (140 mM CsCl) induced an outwardly-rectifying MIC current. The peak amplitude of MIC current and the permeability to divalent cation ($Mn^{2+}$) were several fold higher in Bal-17 than WEHI-231. Also, the level of mRNAs for TRPM7, a molecular correspondence of the MIC channel, was significantly higher in Bal-17 cells. The amplitude of MIC was further increased, and the relation between current and voltage became linear under divalent cation-free conditions, demonstrating typical properties of the TRPM7. The stimulation of B cell receptors (BCR) by ligation with antibodies did not change the amplitude of MIC current. Also, increase of extracellular $[Mg^{2+}]_c$ to enhance the $Mg^{2+}$ influx did not affect the BCR ligation-induced death of WEHI-231 cells. Although the level of TRPM7 was not directly related with the cell death of immature B cells, the remarkable difference of TRPM7 might indicate a fundamental change in the permeability to divalent cations during the development of B cells.

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