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.
Schweigel
Monika
M
Research Unit Nutritional Physiology Oskar Kellner, Research Institute for the Biology of Farm Animals (FBN), Dummerstorf, Germany. mschweigel@fbn-dummerstorf.de
Kuzinski
Judith
J
Deiner
Carolin
C
Kolisek
Martin
M
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