Cobalt uptake and binding in human red blood cells

Area of Science:

• Biochemistry
• Toxicology
• Hematology

Background:

• Cobalt's interaction with biological systems, particularly red blood cells, is crucial for understanding its toxicological effects and potential for biomonitoring.
• Human red blood cells possess mechanisms for cobalt uptake and intracellular binding, influencing its distribution and persistence within the body.

Purpose of the Study:

• To investigate the basal uptake and cytoplasmic binding kinetics of cobalt in human red blood cells.
• To characterize the role of ionophores in cobalt transport and accumulation.
• To explore the binding sites and reversibility of intracellular cobalt, particularly its interaction with hemoglobin.

Main Methods:

• Utilized (57)Co as a radioactive tracer to study cobalt uptake and efflux in human red blood cells.
• Employed ionophore A23187 to facilitate cobalt transport across the cell membrane.
• Analyzed cobalt binding and distribution using techniques like Michaelis-Menten kinetics and Sephadex column chromatography.

Main Results:

• Basal cobalt uptake is linear and nearly irreversible, with a significant portion accumulating intracellularly due to cytoplasmic buffering.
• Ionophore A23187 mediates rapid cobalt equilibration, revealing a low free cobalt ion concentration (α(Co)=0.01) and a maximum buffering capacity.
• Cobalt exhibits both reversible and tightly bound fractions within cells, with tight binding increasing over time and strongly associating with hemoglobin.

Conclusions:

• Cobalt uptake in red blood cells is predominantly irreversible, with tight binding to hemoglobin contributing to its long-term retention.
• The red blood cell's capacity to accumulate and bind cobalt makes it a suitable matrix for biomonitoring long-term cobalt exposure.
• Oxidation of Co(2+) to Co(3+) is a potential mechanism for high-affinity cobalt binding within red blood cells.