Electroneutral transport of organic cations in canine renal brush border membrane vesicles (BBMV).
The effect of potential difference on the organic cation/H+ antiport system located in brush border membrane vesicles was examined. Potential difference was generated using K+ gradients and a K+-specific ionophore, valinomycin. Transport of a prototypic organic cation, 1N-[3H]methylnicotinamide (NMN), was assessed under conditions where K+ diffusion potentials generated transient intravesicular negative and positive states. The results demonstrate that NMN transport is independent of potential difference. The organic cation/H+ coupling ratio was studied by imposing transmembrane H+ and NMN gradients of varying magnitudes and measuring net flux of NMN for a 5-sec period. Consistent with an equilibrium thermodynamics model, no net NMN flux is observed when the NMN gradient from out to in is equal to the H+ gradient from out to in ([NMN]o/[NMN]i equals [H+]o/[H+]i). This suggests that the carrier is at equilibrium and that the stoichiometry for the organic cation/H+ antiport is 1:1.
Sokol
P P
PP
Holohan
P D
PD
Ross
C R
CR
D000818:Animals; D001692:Biological Transport; D002412:Cations / Q000378:metabolism*; D004058:Diffusion; D004285:Dogs; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D009536:Niacinamide / Q000031:analogs & derivatives / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014316:Tritium
D002412:Cations; D014316:Tritium; D009536:Niacinamide; D012964:Sodium; D011188:Potassium; C024058:N(1)-methylnicotinamide