Fast uptake kinetics in vitro of 51Cr (VI) by red blood cells of man and rat

Fast transport kinetics of ⁵¹Cr (VI) into red blood cells (RBCs) in vitro were studied. No significant species differences were found between RBCs of man and rat. The uptake of ⁵¹Cr (VI) by RBCs in whole blood was composed of two different first order processes of different velocities (apparent t_1/2 of 22.7 s and 10.4 min for man and 6.9 s and 10.1 min for rat, respectively). However, even after longer time periods a fixed portion of approximately 15% of the administered dose remained in the plasma and did not penetrate into RBCs Over the entire concentration range studied (10 M–50 mM), the fast initial uptake followed Michaelis-Menten kinetics. The maximal capacity of this Cr(VI) transport into RBCs of man and rat was 3.1×10⁸ CrO₄^2– ions × cell^–1 × min^–1 and 2.5×10⁸ CrO₄^–2 ions × cell^–1 × min^–1, respectively. It is likely that Cr(VI) is transported into RBCs via a physiological anion carrier (band-3-protein).