Abstract
More than 70% of cyclosporine A (CsA) is bound to erythrocytes at whole blood concentrations of 50–1000 ng·ml−1. Cytosolic CsA is bound to the erythrocyte peptidyl-prolyl cis-trans isomerase cyclophilin. Measurements of serum CsA levels under clinical conditions are hampered by a temperature-dependent translocation of CsA into erythrocytes during cooling of the probes to room temperature. In order to characterize the kinetics of CsA uptake and to find a specific uptake inhibitor, we developed a method to measure the velocity of uptake based on rapid cooling of the erythrocyte suspension.
The total erythrocyte-binding capacity for CsA amounted to 43·10−5 nmol per 106 erythrocytes or 2.6·105 molecules per erythrocyte. Whereas the erythrocyte-binding capacity of CsA was temperature-independent between 10°C and 42°C, uptake kinetics of CsA were temperature-dependent. The Arrhenius plot for CsA uptake in human erythrocytes was linear and no transition temperature between 0°C and 42°C could be detected. Therefore the CsA uptake process in human erythrocytes did not fulfil the criteria of carrier-mediated transport.
This indicates that CsA diffuses passively into human erythrocytes. Hence, erythrocyte CsA uptake cannot be specifically inhibited.
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Reichel, C., von Falkenhausen, M., Brockmeier, D. et al. Characterization of cyclosporine a uptake in human erythrocytes. Eur J Clin Pharmacol 46, 417–419 (1994). https://doi.org/10.1007/BF00191903
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DOI: https://doi.org/10.1007/BF00191903