Procainamide transport in rabbit renal cortical brush border membrane vesicles

Area of Science:

• Nephrology
• Renal Physiology
• Molecular Transport

Background:

• Previous research suggested organic cation transport via proton exchange in renal tubules.
• Direct evidence in rabbit proximal tubules was lacking.

Purpose of the Study:

• To directly investigate the mechanism of organic cation transport across the apical membrane of rabbit proximal tubules.
• To confirm the role of organic cation/proton exchange in renal secretion.

Main Methods:

• Utilized [3H]procainamide uptake studies in canine and rat renal cortical brush border membrane vesicles (BBMV).
• Manipulated proton gradients, osmolarity, and ion gradients (Na+, K+) to assess transport.
• Investigated the effect of ionophores (FCCP, valinomycin) and other organic cations.

Main Results:

• Procainamide uptake was stimulated by an outward proton gradient and inhibited by an inward gradient.
• Uptake was saturable, indicating a carrier-mediated process with a specific Km and Vmax.
• Transport was sensitive to ionophores and other organic cations, ruling out nonionic diffusion.

Conclusions:

• The results strongly support an electroneutral organic cation/proton exchange mechanism for procainamide secretion.
• This mechanism operates across the apical cell membrane of rabbit proximal tubules.
• Provides direct evidence for a key renal transport process.