Electroneutral transport of organic cations in canine renal brush border membrane vesicles (BBMV)
Sokol, P.P.; Holohan, P.D.; Ross, C.R.
Journal of Pharmacology and Experimental Therapeutics 233(3): 694-699
1985
ISSN/ISBN: 0022-3565 PMID: 3159885 Document Number: 260472
The effect of potential difference on the organic cation/H+ antiport system located in brush border membrane vesicles was examined in dogs. A potential difference was generated using K+ gradients and a K+-specific ionophore, valinomycin. Transport of a prototypic organic cation, 1H-[3H]methlynicotinamide (NMN), was assessed under conditions where K+ diffusion potentials generated transient intravesicular negative and positive states. NMN transport is apparently 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 s period. Consistent with an equilibrium thermodynamics model, no net NMN flux was observed when the NMN gradient from out to in was equal to the H+ gradient from out to in ([NMN]o/[NMN] equals [H+]o/[H+]i). The carrier is apparently at equilibrium and the stoichiometry for the organic cation/H+ antiport is 1:1.