Effect of cadmium ions on dioxygen affinity and polyphosphate activity of human red blood cells

Summary

The effect of cadmium ions on the dioxygen affinity, the time-dependent depletion of intracellular polyphosphates, and the elongation of human red blood cells (RBC's) was examined. The incubation of RBC's in the presence of 1 mM Cd²⁺ at 37°C for more than one hour results in a decrease of the p₅₀ value by 2.5–3.0 mmHg in comparison to controls. The p₅₀ of stripped (phosphate-free) hemoglobin is not affected by the presence of 1 mM Cd²⁺ (p₅₀=4.8 mmHg at pH 7.2 and 37°C). Experiments with RBC cryolysates demonstrate an apparently competitive effect of 2.3-bisphosphoglycerate (DPG) with cadmium ions on the dioxygen affinity. From ³¹P NMR spectra, ³¹P T₁ relaxation, and ³¹P T₂ relaxation behavior a more direct evidence for DPG-Cd²⁺ complexation is obtained. ³¹P NMR spectra of RBC cryolysates also indicate DPG-Cd²⁺ complexation. The hydrolysis of free polyphosphates in RBC's incubated at 37°C as monitored by ³¹P NMR spectra can be noticed after a three-hour lag phase (constant polyphosphate level). This lag phase is lengthened from three hours to four hours in the presence of Cd²⁺ ions. RBC elongation, as a measure of deformability, decreases slightly upon incubation with 1 mM Cd²⁺.