title: [3H]Ethylpropylamiloride, a ligand to analyze the properties of the Na+/H+ exchange system in the membranes of normal and hypertrophied kidneys.
abstract: [3H]Ethylpropylamiloride is a useful radioactive label to identify the Na+/H+ exchange system (Vigne, P., Frelin, C., Audinot, M., Borsotto, M., Cragoe, E. J., and Lazdunski, M. (1984) EMBO J. 3, 2647-2651). This paper extends the analysis of the properties of interaction of [3H]ethylpropylamiloride with the exchanger and describes its use with hypertrophied kidneys. [3H]Ethylpropylamiloride-binding sites copurify with the luminal membrane marker alkaline phosphatase but not with the basolateral membrane marker (Na+,K+)ATPase, thus indicating an asymmetric distribution of the Na+/H+ exchanger. Specific [3H]ethylpropylamiloride binding is dependent on pH. The pH dependency indicates that an ionizable function with a pKapp of 7.0 is essential in the association of the amiloride derivative. H+ acts competitively on [3H]ethylpropylamiloride binding; Na+, Li+, or cholinium ions have no effect on the association. Compensatory adaptation of the kidney to chronic reduction of renal mass is accompanied by a 1.7-fold increase in the activity of the Na+/H+ exchange system. Properties of interaction of internal and external pH with the Na+/H+ exchanger of normal and hypertrophied kidneys are identical. Titration of [3H]ethylpropylamiloride-binding sites in normal and hypertrophied kidneys suggests that the increased activity of the Na+/H+ exchange system is not accompanied by an increased concentration of exchangers.
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006984:Hypertrophy / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008094:Lithium / Q000494:pharmacology; D011522:Protons; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers; D014316:Tritium
chemical_list: D002352:Carrier Proteins; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D014316:Tritium; C043988:5-(ethylpropyl)amiloride; D000584:Amiloride; D008094:Lithium; D012964:Sodium