title: Sodium-proton exchange in colon brush-border membranes.
abstract: Apical membrane vesicles were prepared from proximal and distal segments of the large intestine of the rat by a method based on morphological criteria and were used to determine 22Na uptake. In both preparations an outwardly directed proton gradient stimulated 22Na uptake. In proximal colon a decrease in vesicular volume induced by an increased media osmolarity led to diminished 22Na uptake at 90 min; a significant (50-60%) portion of uptake represented binding. Initial uptake was linear for 10 s and extrapolated through zero, indicating minimal extravesicular binding. Initial uptake was a saturable function of medium Na concentration. In both preparations initial influx of 0.1 mM NaCl was inhibited by amiloride (0.1-1.0 mM), 15 mM NaCl, 15 mM LiCl, and 15 mM NH4Cl. From the characteristics of the initial 22Na influx we conclude that the apical membrane from colonocytes of proximal and distal segments contains a Na-H exchange with properties similar to those described in other epithelia.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D018021:Lithium Chloride; D008297:Male; D008871:Microvilli / Q000378:metabolism*; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D012979:Sodium Radioisotopes; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D002712:Chlorides; D011522:Protons; D012979:Sodium Radioisotopes; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; D012965:Sodium Chloride; D000584:Amiloride; D008094:Lithium; D012964:Sodium; D018021:Lithium Chloride