Polarized Na+/H+ exchange function is pliable in response to transepithelial gradients of propionate.
Short-chain fatty acids are produced at high concentration in the colonic lumen and stimulate electroneutral Na+ absorption by activating apical Na+/H+ exchange in colonocytes. We used an epithelial cell line derived from a human colon carcinoma (HT29-18-C1) to study activation of apical and basolateral Na+/H+ exchange by a short-chain fatty acid, propionate. Confluent cell monolayers on membrane filters were loaded with 2',7'-bis(2-carboxyethyl)-5 (and 6)-carboxyfluorescein (a fluorescent pH indicator) and intracellular pH was monitored with a digital fluorescence imaging microscope. Cells acidified by transient exposure to NH4Cl demonstrated both apical and basolateral Na+/H+ exchange. In this condition, apical Na+/H+ exchange was 50% of the total Na+/H+ exchange activity. Similar results were obtained when cells were bilaterally perfused with apical and basolateral propionate in an isosmotic medium (130 mM propionate at each membrane surface). However, apical Na+/H+ exchange was a significantly larger fraction (76%) of the total Na+/H+ exchange activity when cells were acidified by exposure to apical propionate alone. Conversely, in cells acidified by basolateral propionate alone, apical Na+/H+ exchange was 21% of the total Na+/H+ exchange activity. The change in relative activity was observed in individual cells which expressed both apical and basolateral Na+/H+ exchange and occurred rapidly (within 7 min). In the presence of transepithelial propionate gradients, all Na(+)-dependent alkalinization was sensitive to 3 microM 5-(N-ethyl-N-isopropyl)amiloride, a potent Na+/H+ exchange inhibitor. These results suggest that transepithelial gradients of short-chain fatty acids, which occur in vivo, can cause preferential activation of apical Na+/H+ exchange.
Rowe
W A
WA
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Lesho
M J
MJ
Montrose
M H
MH
D000643:Ammonium Chloride / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003110:Colonic Neoplasms; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011422:Propionates / Q000494:pharmacology*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D011422:Propionates; D000644:Quaternary Ammonium Compounds; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; D012964:Sodium; C027917:tetramethylammonium; C029658:propionic acid