Rumen epithelial cells adapt magnesium transport to high and low extracellular magnesium conditions.
A protein of approximately 70-kDa was identified as a candidate Na+/Mg2+ exchanger in rumen epithelial cells (REC). Melastatin-related Transient Receptor Potential 7 (TRPM7) and Magnesium Transporter 1 (MagT1) transcripts and, from them, encoded proteins were also detected. The regulation of these Mg transport pathways by extracellular [Mg] changes was the main focus of this study. Therefore, a 24-h pre-incubation of ovine REC in control (1.2 mM), low (0.12 mM)-Mg, and high (5 mM)-Mg medium was performed. Na+/Mg2+ exchangers, TRPM7 and MagT1 abundance and activity were investigated by Western blot analysis, flow cytometry, immunocytochemistry and fluorescence spectroscopic measurements of [Mg2+]i changes. Inhibitors were employed to differentiate Na+/Mg2+ exchanger-mediated (imipramine) and channel-mediated (cobalt(III)hexaammine, nitrendipine) Mg transport. Basal [Mg2+]i (0.40 +/- 0.02 mM) was not influenced by pre-incubation in low- or high-Mg medium. However, compared with control REC (4.1 +/- 0.7 microM/min), such cells showed reduced (2.8 +/- 0.6 microM/min) or elevated (6.4 +/- 0.9 microM/min) Mg extrusion rates that correlated with a decreased (25%) and increased (38%) expression of the putative Na+/Mg2+ exchanger protein, respectively. Low- and high-Mg pre-incubated REC were both characterized by an increased (30-40%) influx capacity. In low-Mg REC, the latter resulted mainly from a strong activation of the TRPM7-related transport component. The data thus clearly demonstrate the intrinsic regulation of REC transmembrane Mg transport.
Research Unit Nutritional Physiology Oskar Kellner, Research Institute for the Biology of Farm Animals (FBN), Dummerstorf, Germany. mschweigel@fbn-dummerstorf.de
Monika
M
Schweigel
Judith
J
Kuzinski
Carolin
C
Deiner
Martin
M
Kolisek
D000818:Animals; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism*; D005434:Flow Cytometry; D007150:Immunohistochemistry; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D012313:RNA / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012417:Rumen / Q000166:cytology* / Q000378:metabolism; D015398:Signal Transduction; D050053:TRPM Cation Channels / Q000235:genetics
D050053:TRPM Cation Channels; C459082:TRPM6 protein, human; D012313:RNA; D017346:Protein Serine-Threonine Kinases; C486583:TRPM7 protein, human; D008274:Magnesium