Cadmium uptake by brush border membrane vesicles from the rabbit renal external cortex

Area of Science:

• Nephrology
• Toxicology
• Biochemistry

Background:

• Inorganic cadmium (Cd) is a toxic heavy metal that can accumulate in the kidneys.
• Understanding the initial steps of cadmium entry into renal cells is crucial for assessing its toxicity.

Purpose of the Study:

• To investigate the mechanism of inorganic cadmium uptake by rabbit renal brush border membrane vesicles (BBMV).
• To determine the role of membrane binding versus intravesicular accumulation in cadmium uptake.
• To assess the influence of pH on cadmium binding to the BBMV.

Main Methods:

• Isolation of brush border membrane vesicles (BBMV) from rabbit renal external cortex.
• Incubation of BBMV with varying concentrations of inorganic cadmium (10-200 µmol/L) over time (1-60 min).
• Determination of cadmium uptake using a rapid filtration technique and experiments involving osmotic shock and osmolality variations.

Main Results:

• Cadmium uptake by BBMV was both time- and concentration-dependent.
• At low Cd concentrations, uptake was rapid and nearly complete within 1 minute.
• At high Cd concentrations, a slower uptake component appeared, and experiments indicated uptake was primarily due to membrane binding, not intravesicular accumulation.
• A decrease in pH from 7.4 to 5.8 removed approximately 40% of bound Cd, demonstrating pH-sensitive binding.

Conclusions:

• Cadmium uptake by renal BBMV is predominantly mediated by binding to the brush border membrane.
• This membrane binding is a pH-sensitive process.
• Brush border membrane binding represents the initial critical step for inorganic cadmium entry into renal epithelial cells.