title: Proton-coupled organic cation transport in renal brush-border membrane vesicles.
abstract: We had previously proposed that organic cations are transported across the brush-border membrane in the canine kidney by a H+ exchange (or antiport) system (Holohan, P.D. and Ross, C.R. (1981) J. Pharmacol. Exp. Ther. 216, 294-298). In the present report, we demonstrate that in brush-border membrane vesicles the transport of organic cations is chemically coupled to the countertransport of protons, by showing that the uphill or concentrative transport of a prototypic organic cation, N1-methylnicotinamide (NMN), is chemically coupled to the flow of protons down their chemical gradient. In a reciprocal manner, the concentrative transport of protons is coupled to the counterflow of organic cations down their concentration gradient. The transport of organic cations is monitored by measuring [3H]NMN while the transport of protons is monitored by measuring changes in acridine orange absorbance. The functional significance of the coupling is that a proton gradient lowers the Km and increases the Vmax for NMN transport.
mesh_terms: D000165:Acridine Orange; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002412:Cations; D004285:Dogs; D004563:Electrochemistry; D006096:Gramicidin / Q000494:pharmacology; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism*; D009536:Niacinamide / Q000031:analogs & derivatives* / Q000378:metabolism; D009550:Nigericin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011522:Protons; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D013053:Spectrophotometry; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D002412:Cations; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D006096:Gramicidin; D014634:Valinomycin; D009536:Niacinamide; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D012964:Sodium; D000165:Acridine Orange; D009550:Nigericin; D011188:Potassium; C008472:N-methylnicotinamide