title: High glucose concentration stimulates NHE-1 activity in distal nephron cells: the role of the Mek/Erk1/2/p90RSK and p38MAPK signaling pathways.
abstract: OBJECTIVE
  In models of diabetes, distal nephron cells contribute to glucose uptake and oxidation. How these cells contribute to the use of glucose for the regulation of H(+) extrusion remains unknown. We used Madin-Darby Canine Kidney (MDCK) cells to investigate the effect of acute or chronic high glucose concentration on the abundance and activity of the Na(+)/H(+) exchanger (NHE-1).
  
  
  METHODS
  Using RT-PCR, we also evaluated the mRNA expression for sodium glucose co-transporters SGLT1 and SGLT2. Protein abundance was analyzed using immunoblotting, and intracellular pH (pHi) recovery was evaluated using microscopy in conjunction with the fluorescent probe BCECF/AM. The Na(+)-dependent pHi recovery rate was monitored with HOE-694 (50 µM) and/or S3226 (10 µM), specific NHE-1 and NHE-3 inhibitors.
  
  
  RESULTS
  MDCK cells did not express the mRNA for SGLT1 or SGLT2 but did express the GLUT2, NHE-1 and NHE-3 proteins. Under control conditions, we observed a greater contribution of NHE-1 to pHi recovery relative to the other H(+) transporters. Acute high glucose treatment increased the HOE-694-sensitive pHi recovery rate and p-Erk1/2 and p90(RSK) abundance. These parameters were reduced by PD-98059, a Mek inhibitor (1 µM). Chronic high glucose treatment also increased the HOE-694-sensitive pHi recovery rate and p-p38MAPK abundance. Both parameters were reduced by SB-203580, a p38MAPK inhibitor (10 µM).
  
  
  CONCLUSIONS
  These results suggested that extracellular high glucose stimulated NHE-1 acutely and chronically through Mek/Erk1/2/p90(RSK) and p38MAPK pathways, respectively.
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Science, University of São Paulo, São Paulo, Brazil.
authors.forename: Juliana Martins
authors.initials: JM
authors.lastname: da Costa-Pessoa
authors.forename: Rosélia Santos
authors.initials: RS
authors.lastname: Damasceno
authors.forename: Ubiratan Fabres
authors.initials: UF
authors.lastname: Machado
authors.forename: Olívia
authors.initials: O
authors.lastname: Beloto-Silva
authors.forename: Maria
authors.initials: M
authors.lastname: Oliveira-Souza
mesh_terms: D000818:Animals; D004285:Dogs; D005947:Glucose / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007686:Kidney Tubules, Distal / Q000166:cytology / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D061985:Madin Darby Canine Kidney Cells; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism*; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D013549:Sweetening Agents / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D017923:Sodium-Hydrogen Exchangers; D013549:Sweetening Agents; C069139:growth factor-activatable Na-H exchanger NHE-1; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; D005947:Glucose