An ATP-driven proton pump in brush-border membranes from rat renal cortex

Area of Science:

• Biochemistry
• Renal Physiology
• Membrane Biology

Background:

• The luminal membrane of renal cortical tubules plays a critical role in ion transport and maintaining acid-base balance.
• Understanding the mechanisms of proton (H+) transport is essential for comprehending kidney function.

Purpose of the Study:

• To investigate the rate of ATP hydrolysis and H+ secretion in plasma membrane vesicles from renal cortical tubules.
• To identify the presence and characteristics of an ATP-driven proton pump in the luminal membrane.

Main Methods:

• Utilized ATP-preloaded plasma membrane vesicles derived from the luminal membrane of renal cortical tubules.
• Assessed ATP hydrolysis and H+ secretion rates under various conditions, including temperature changes, filipin treatment, and specific channel blockers (dicyclohexylcarbodiimide, Dio-9).
• Examined the effects of valinomycin, K+, and the protonophore carbonyl-cyanid-p-trifluormethoxy-phenylhydrazone on vesicle function.
• Monitored pH changes in the extravesicular medium and their impact on ATP hydrolysis.

Main Results:

• Both ATP hydrolysis and H+ secretion were inhibited by low temperature, filipin (cholesterol complexation), and mitochondrial Fo hydrogen channel blockers.
• Valinomycin with K+ showed a stimulatory effect on the process.
• The protonophore carbonyl-cyanid-p-trifluormethoxy-phenylhydrazone stimulated intravesicular ATP hydrolysis and abolished extravesicular acidification.
• Extravesicular pH changes influenced ATP hydrolysis rates, with lower pH retarding and readjustment accelerating it.

Conclusions:

• The observed inhibition and stimulation patterns strongly support the presence of an ATP-driven proton pump.
• This proton pump is localized in the luminal membrane of renal cortical tubules.
• The findings provide evidence for a key mechanism in renal proton secretion and acid-base regulation.