NHE3-dependent cytoplasmic alkalinization is triggered by Na(+)-glucose cotransport in intestinal epithelia.
Cytoplasmic pH (pH(i)) was evaluated during Na(+)-glucose cotransport in Caco-2 intestinal epithelial cell monolayers. The pH(i) increased by 0.069 +/- 0.002 within 150 s after initiation of Na(+)-glucose cotransport. This increase occurred in parallel with glucose uptake and required expression of the intestinal Na(+)-glucose cotransporter SGLT1. S-3226, a preferential inhibitor of Na(+)/H(+) exchanger (NHE) isoform 3 (NHE3), prevented cytoplasmic alkalinization after initiation of Na(+)-glucose cotransport with an ED(50) of 0.35 microM, consistent with inhibition of NHE3, but not NHE1 or NHE2. In contrast, HOE-694, a poor NHE3 inhibitor, failed to significantly inhibit pH(i) increases at <500 microM. Na(+)-glucose cotransport was also associated with activation of p38 mitogen-activated protein (MAP) kinase, and the p38 MAP kinase inhibitors PD-169316 and SB-202190 prevented pH(i) increases by 100 +/- 0.1 and 86 +/- 0.1%, respectively. Conversely, activation of p38 MAP kinase with anisomycin induced NHE3-dependent cytoplasmic alkalinization in the absence of Na(+)-glucose cotransport. These data show that NHE3-dependent cytoplasmic alkalinization occurs after initiation of SGLT1-mediated Na(+)-glucose cotransport and that the mechanism of this NHE3 activation requires p38 MAP kinase activity. This coordinated regulation of glucose (SGLT1) and Na(+) (NHE3) absorptive processes may represent a functional activation of absorptive enterocytes by luminal nutrients.
Turner
J R
JR
Department of Pathology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA. jturner@bsd.uchicago.edu
Black
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D000205:Actomyosin / Q000378:metabolism; D015153:Blotting, Western; D018938:Caco-2 Cells; D003593:Cytoplasm / Q000187:drug effects / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051269:Sodium-Glucose Transporter 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; C495674:SLC5A1 protein, human; C000613385:SLC9A3 protein, human; D051269:Sodium-Glucose Transporter 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000205:Actomyosin; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases